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FOOTHILLS MALL REDEVELOPMENT, PHASE ONE - PDP/FDP - FDP130040 - SUBMITTAL DOCUMENTS - ROUND 1 - RECOMMENDATION/REPORT
41 Inverness Drive East, Englewood, CO 80112-5412 Phone (303) 289-1989 Fax (303) 289-1686 www.groundeng.com Office Locations: Englewood Commerce City Loveland Granby Gypsum Grand Junction Casper Subsurface Exploration Program Geotechnical and Pavement Recommendations Foothills Mall Redevelopment – Retail/Commercial Structures Fort Collins, Colorado FINAL Submittal Prepared for: Walton Foothills Holdings, VI, LLC 5750 DTC Parkway, Suite 210 Greenwood Village, Colorado 80111 Attention: Mr. Adam Radcliffe Job Number: 12-3649A December 17, 2012 EXECUTIVE SUMMARY The content in the report provides geotechnical and pavement design recommendations for the Foothills Mall Redevelopment. Below is a summary of the information contained in the report for Phases 1 through 3. The subsurface conditions encountered in the test holes generally consisted of a thin veneer of asphalt, approximately 4 to 7 inches thick, or concrete, approximately 5 inches (interior of the building), underlain by sand and/or clay and gravel. These materials were underlain by sandstone and claystone bedrock at depths ranging from approximately 12 to 24 feet below existing grade. The test holes extended to depths ranging from approximately 5 to 40 feet below the existing grades. Groundwater was encountered in the test holes at depths ranging 11 to 27 feet below existing grade at the time of drilling. Temporary piezometers were installed three (3) of the test holes (Test Holes, 30, 36, and 39) in order to observe groundwater levels. Groundwater was encountered at depths ranging from 12 to 19 feet when measured 7 and 14 days following drilling. Groundwater levels can be expected to fluctuate, however, in response to annual and longer-term cycles of precipitation, irrigation, surface drainage, nearby rivers and creeks, land use, and the development of transient, perched water conditions. Prior to filling the existing drainage ditch, once at competent, stable materials, the placement of a large drain/pipe surrounded with clean crushed rock on the order of 10 feet wide or to the lateral extents of the drainage and wrapped with a separating geotextile should installed. Where fill is to be placed within the drainage, the slopes should be benched. The benches shall be cut 3 feet horizontally into the existing slope to create a stepped bench condition and compacted to 100 percent of the standard Proctor or 98 percent of the modified Proctor. Below is a summary of the recommended foundation/floor systems for each Phase/Building area along with the recommended overexcavation and replacement to reduce the potential for movement associated with total and differential movements. Please refer to the report for a detailed explanation of these systems. The minimum pavement sections recommended by GROUND based on our traffic assumptions are tabulated below. Recommended Minimum Pavement Sections Location Full Depth Asphalt (inches Asphalt) Composite Section (inches Asphalt / inches Aggregate Base) Rigid Section (inches Concrete) Private Parking Lot 6 4.5 / 6 5 Private Drive Lanes and Heavy Truck Traffic 6.5 5 / 6 6 Additional recommendations with respect to foundations and floor systems for each Phase and building type, water-soluble sulfates, corrosivity, exterior flatwork, project earthworks, excavation conditions, utility installation, surface drainage, perimeter underdrains, pavement sections are contained herein. This executive summary should not be solely relied upon as a complete summary of the information contained in this report; rather the entire contents of this report should be reviewed by the Client/Owner/Project Team prior to design/construction. Location Foundation/Floor Type Overexcavation beneath Shallow Foundation/Slab- on-Grade* Phase 1 - Block 7 to 10 Spread Footings/Slab-on- Grade 12-inch Scarification beneath Footings and Slabs Phase 1 – Existing Mall Renovation/Reconstruction Spread Footings/Slab-on- Grade (if applicable) Undisturbed On-site Material/12-inch Scarification Phase 1 – Restaurant (Rest. 1 to 4) Spread Footings/Slab-on- Grade Uniform Fill Prism Phase 1 – Parking Garage Drilled Piers / Slab-on- Grade Floors 12-inch Scarification beneath Slabs Phase 1 – Cinema Drilled Piers or Spread Footings/ Slab-on-Grade Floors Uniform Fill Prism or 12- inch Scarification beneath Footings and Slabs Phase 2 – Blocks 1 to 3 Spread Footings/Slab-on- TABLE OF CONTENTS Page Purpose and Scope of Study ...................................................................................... 1 Proposed Construction ................................................................................................ 1 Site Conditions ............................................................................................................ 3 Subsurface Exploration ............................................................................................... 5 Laboratory Testing ...................................................................................................... 6 Subsurface Conditions ................................................................................................ 7 Engineering Seismicity .............................................................................................. 10 Drainage Improvements ................................................................................................ 11 Foundation/Floor System Overview ............................................................................ 13 Foundation System ................................................................................................... 18 Floor System ............................................................................................................. 24 Mechanical Rooms/Mechanical Pads ........................................................................... 27 Exterior Flatwork ....................................................................................................... 27 Water Soluble Sulfates ................................................................................................ 30 Soil Corrosivity ............................................................................................................ 31 Lateral Earth Pressures ............................................................................................ 34 Project Earthwork ...................................................................................................... 36 Excavation Considerations ........................................................................................ 41 Utility Pipe Installation and Backfilling ......................................................................... 42 Surface Drainage ...................................................................................................... 45 Underdrain/Subsurface Moisture Infiltration ............................................................... 48 Pavement Conclusions/Recommendations ................................................................ 49 Closure and Limitations ............................................................................................. 57 Locations of Test Holes ..................................................................................... Figure 1 Logs of Test Holes ...................................................................................... Figures 2-6 Legend and Notes ............................................................................................. Figure 7 Compaction Test Results ................................................................................ Figures 8-9 Summary of Laboratory Test Results ................................................................ Table 1 Summary of Soil Corrosion Test Results .............................................................. Table 2 Percolation Test Results – I1 ................................................................................ Table 3 Percolation Test Results – I2 ................................................................................ Table 4 Geophysical Investigation Report .............................................................. Appendix A Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 1 of 60 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsurface exploration program performed by GROUND Engineering Consultants, Inc. (GROUND) to provide geotechnical and pavement recommendations for the proposed Foothills Mall Redevelopment located near the intersection of South College Avenue and East Foothills Parkway in Fort Collins, Colorado. Our study was conducted in general accordance with GROUND Proposal No. 1207-1089 Revised, dated September 13, 2012. Field and office studies provided information regarding surface and subsurface conditions, including existing site vicinity improvements and groundwater. Material samples retrieved during the subsurface exploration were tested in our laboratory to assess the engineering characteristics of the site earth materials, and assist in the development of our geotechnical recommendations. Results of the field, office, and laboratory studies for the proposed facility are presented below. This report has been prepared to summarize the data obtained and to present our conclusions and recommendations based on the proposed construction and the subsurface conditions encountered. Design parameters and a discussion of engineering considerations related to construction of the proposed facility are included herein. PROPOSED CONSTRUCTION We understand that the proposed project is comprised of four phases. Phases 1 through 3 are addressed by this report, while Phase 4 will be presented in a separate, forthcoming report. The following presents a brief summary of the proposed construction/reconstruction associated with Phases 1 through 3. Phase 1: Renovation/demolition and construction of retail/commercial facilities adjacent to/attached to the existing Foothills Mall. Building footprints will range in size from approximately 7,000 square feet to approximately 35,000 square feet. Additionally, a cinema structure, approximately 76,215 square feet in size, and a parking garage are planned for construction. According to provided grading plans, finish floor elevations (FFEs) for Retail Blocks 7 through 10 will range from approximately 5,017.5 feet to 5,020 feet, FFEs for Restaurants 1 to 4 (Rest. 1 to 4) will range from approximately 5,017 feet Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 2 of 60 to 5,018 feet, FFEs for the cinema will range from 5,017 feet to 5,018 feet, and FFEs for the parking structure will range from approximately 5,009.5 feet to 5,016.8 feet. The existing mall consists of FFEs ranging from approximately 5,017 feet to 5,020 feet. Therefore, it appears that material cuts up to approximately 3 feet and material fills up to approximately 5 feet will be necessary to facilitate proposed construction. Phase 2: Demolition of existing buildings and construction of five (5) retail buildings ranging in size from approximately 6,514 square feet to approximately 20,393 square feet. According to provided grading information, FFEs ranging from approximately 5,014 feet to 5,021 feet are planned for Blocks 1 through 3. Therefore, it appears that material cuts up to approximately 1 foot and material fills up to approximately 4 feet will be necessary to facilitate proposed construction. Phase 3: Demolition of existing buildings and construction of four (4) retail buildings ranging in size from approximately 7,415 square feet to approximately 35,590 square feet. According to provided grading information, FFEs ranging from approximately 5,024 feet to 5,033 feet are planned for Blocks 4 through 6. Therefore, it appears that material cuts up to approximately 1 foot and material fills up to approximately 8 feet will be necessary to facilitate proposed construction. Additionally, the existing drainage ditch currently traversing the Phase 3 area may be relocated to the west along South College Avenue to accommodate new building construction. According to the project structural engineer, the parking garage will include maximum loads ranging from approximately 1,000 to 1,250 kips and the anticipated building loads for the Cinema will be approximately 100 kips. Additionally, we assume that no basements are anticipated for the proposed structures and the existing buildings do not consist of basement/below-grade levels. The approximate proposed building(s) layouts are shown in Figure 1. Development will also include installation of underground utilities to service the proposed development. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 3 of 60 SITE CONDITIONS Phase 1 At the time of our field exploration, the Phase 1 project area consisted of the existing Foothills Mall facility and asphalt-paved parking areas and drive lanes. GROUND attempted to retrieve as-built drawings or information regarding the existing foundation system, however this information was unavailable at the time of this report preparation. During our site reconnaissance at the time of exploration, the existing mall facility appeared to be performing satisfactorily with no obvious apparent distress. Additionally, according to correspondence with facility maintenance personnel, the mall structure has been performing satisfactorily. The pavement areas exhibited low severity distress on the north side of the building and moderate to high severity distress along the west, east, and south sides of the building, likely due to age and lack of maintenance (see Pavement Conclusions/Recommendations section). Landscaping islands and curb-and-gutter were also associated with the project site. A vacant, undeveloped lot (see photo above) exists on the south side of the existing mall structure. The southern area of the mall is vacated in preparation for future construction. The general topography across the project site was gently sloping with slopes up to approximately 5 percent descending toward the east. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 4 of 60 Phase 2 The Phase 2 project area consisted of existing retail facilities and asphalt-paved parking and drive lanes. As-built drawings for these structures were also unavailable at the time of this report preparation. During our exterior site reconnaissance, the existing retail structures appeared to be performing satisfactorily. However, the pavement areas as exhibited in the photo, consisted of medium severity pavement distress (see Pavement Conclusions/Recommendations section). The distressed areas have been previously crack sealed. The general topography across the project site was relatively flat with slopes up to approximately 2 percent descending toward the northeast. Phase 3 The Phase 3 project area consisted of existing retail facilities, asphalt- paved parking and drive lanes, and short to medium grasses and weeds and deciduous trees. As- built drawings for these structures were also unavailable at the time of this report preparation. During our exterior site reconnaissance, the existing structures appeared aged and not well maintained. However, the pavement areas displayed medium severity pavement distress (see Pavement Conclusions/Recommendations section). An existing drainage ditch ranging from approximately 5 to 8 feet in depth traverses the project area. Standing water and wet conditions were observed in the drainage ditch during our exploration. Pedestrian Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 5 of 60 bridges were also associated with the existing drainage. The general topography across the project site was relatively flat with slopes up to approximately 2 percent descending toward the northeast with steeper slopes associated with the existing drainage ditch. Although not obviously encountered in the test holes, man-made fill may exist on-site. The exact extents, limits, and composition of any man- made fill were not determined as part of the scope of work addressed by this study, and should be expected to potentially exist at varying depths and locations across the site. SUBSURFACE EXPLORATION The subsurface exploration for the project was conducted in September and early October, 2012. A total of fifty-one (51) test holes were drilled with a truck- mounted, continuous flight power auger rig and limited access drill rig to evaluate the subsurface conditions as well as to retrieve soil and bedrock samples for laboratory testing and analysis. Forty (40) test holes were drilled within/adjacent to the proposed building footprints and eleven (11) test holes were drilled within the private paved areas. The test holes were advanced to depths ranging from approximately 5 to 40 feet below existing grade. A representative of GROUND directed the subsurface exploration, logged the test holes in the field, and prepared the soil and bedrock samples for transport to our laboratory. Monitoring/observation holes were installed in Test Holes 30, 36, and 39 at the time of our field exploration in order to temporarily observe groundwater levels. Additionally, Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 6 of 60 infiltration testing was completed on test holes within the eastern portion of the project site within the area proposed for water quality. For this testing, two (2) profile test holes and six (6) percolation test holes were drilled in order to obtain percolation rates. Samples of the subsurface materials were retrieved with a 2-inch I.D. California liner sampler. The sampler was driven into the substrata with blows from a 140-pound hammer falling 30 inches. This procedure is similar to the Standard Penetration Test described by ASTM Method D1586. Penetration resistance values, when properly evaluated, indicate the relative density or consistency of soils. Depths at which the samples were obtained and associated penetration resistance values are shown on the test hole logs. The approximate locations of the test holes are shown in Figure 1. Logs of the exploratory test holes are presented in Figures 2 through 6. Explanatory notes and a legend are provided in Figure 7. GROUND utilized the Client-provided site plan indicating existing features, etc., to approximately locate the test holes. Test Holes 6, 7, and 12 were not able to be drilled during our exploration program due to Owner access restrictions with Sears. LABORATORY TESTING Samples retrieved from our test holes were examined and visually classified in the laboratory by the project engineer. Laboratory testing of soil and bedrock samples obtained from the subject site included standard property tests, such as natural moisture contents, dry unit weights, grain size analyses, swell-consolidation potential, direct shear testing, unconfined compressive strength, and liquid and plastic limits. Water-soluble sulfate and corrosivity tests were completed on selected samples of the soils as well. A Proctor test was completed on the representative composite bulk sample. Laboratory tests were performed in general accordance with applicable ASTM and AASHTO protocols. Results of the laboratory testing program are summarized on Tables 1 and 2. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 7 of 60 SUBSURFACE CONDITIONS Geologic Setting The subject parcel consists largely of a sequence of sedimentary rock formations deposited and preserved in a structural depression in north-central Colorado. In the general project area, these sedimentary rocks dip eastward at low angles (less than 10 degrees, typically) and are overlain by a variety of surficial deposits including alluvial (stream-laid) sediments, eolian (wind-blown) materials and colluvial (slope-wash) deposits. The bedrock deposits underlying the project area are mapped as Upper Cretaceous Pierre Shale (upper unit and sandstone members) (Colton, 19781). In the project vicinity, this formation consists predominately of shale, interbedded locally with siltstones or sandstones. The sands/clays encountered above the Pierre Shale at the site are interpreted to be alluvial deposits of the Pleistocene Slocum Alluvium. Based on the published information reviewed for the site and our experience within Denver, there are no mapped geologic hazards within or directly adjacent to the project site. Phase 1 The subsurface conditions encountered in the test holes generally consisted of a thin veneer of asphalt, approximately 4 to 7 inches thick, or concrete, approximately 5 inches (interior of the building), underlain by sand and/or clay and gravel. These materials were underlain by sandstone and claystone bedrock at depths ranging from approximately 12 to 24 feet below existing grade. The test holes extended to depths of approximately 5 to 40 feet below existing grades. Groundwater was encountered in some of the test holes at depths ranging from approximately 11 to 27 feet below existing grades at the time of drilling. The test holes were backfilled immediately following drilling operations. Groundwater was not 1 Colton, Roger, 1978, Geologic Map of the Boulder, Fort Collins, and Greeley Area, Colorado, USGS Map I- 855G Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 8 of 60 encountered in the test holes drilled within the interior of the mall at the time of our exploration program. Phase 2 The subsurface conditions encountered in the test holes generally consisted of a thin veneer of asphalt/concrete, approximately 5 to 6 inches thick, underlain by sand and/or clay. These materials were underlain by sandstone and claystone bedrock at depths ranging from approximately 14 to 18 feet below existing grade. The test holes extended to depths of approximately 20 to 30 feet below existing grades. Groundwater was encountered in each of the test holes at depths ranging from approximately 10.5 to 13 feet below existing grades at the time of drilling. GROUND constructed Test Hole 30 as an observation/monitoring hole in order to temporarily observe groundwater levels. Groundwater was encountered in this test holes at a depth of approximately 12 feet when measured 7 and 14 days later. The remainder of the test holes were backfilled immediately following drilling operations. Phase 3 The subsurface conditions encountered in the test holes generally consisted of a thin veneer of asphalt/concrete, approximately 2 to 5 inches thick, underlain by sand and/or clay and gravel. These materials were underlain by sandstone and claystone bedrock at depths ranging from approximately 13 to 23 feet below existing grade. The test holes extended to depths of approximately 20 to 30 feet below existing grades. Groundwater was encountered in some of the test holes at depths ranging from approximately 13 to 18 feet below existing grades at the time of drilling. GROUND constructed Test Holes 36 and 39 as observation/monitoring holes in order to temporarily observe groundwater levels. Groundwater was encountered in these test holes at depths of approximately 17 to 19 feet when measured 7 and 14 days later. The remainder of the test holes were backfilled immediately following drilling operations. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 9 of 60 Subsurface Materials Sand and Clay were interbedded, fine to meduim grained, low to highly plastic, medium to very stiff/loose to medium dense, slightly moist to moist, light brown to reddish brown in color, and occasionally calcareous. Sand was silty to clayey, medium to coarse grained with occasional gravel, non-plastic to low plastic, medium dense to dense, moist to wet, and reddish brown to light brown in color. Sand and Gravel were interbedded, coarse to gravel grained, non-plastic to low plastic, medium dense to very dense, moist to wet, and reddish brown in color. Sandstone and Claystone Bedrock (Comparably Unweathered Bedrock) were interbedded, fine to medium grained, low to highly plastic, hard to very hard, dry to moist, light brown in color, and occasionally iron-stained. Sandstone Bedrock (Comparably Unweathered Bedrock) was silty to clayey, medium to coarse grained, low plastic, hard to resistant, dry to moist, light brown in color, and occasionally iron-stained. Please note that the sandstone may be cemented and relatively resistant, which may complicate excavation such as deep foundations. Swell-Consolidation Testing of samples of the on-site materials encountered in the project test holes indicate a potential for heave/consolidation (See Table 1). Swells ranging from approximately 0.1 to 0.6 percent and consolidations of approximately 0.1 to 4.3 percent were also measured at various surcharge loads. Percolation Testing Percolation testing was performed in the associated test holes at a depth of approximately 36 inches below existing grade. GROUND utilized the testing procedures indicated in Laramie County Small Wastewater Systems Regulations to perform our field analysis. Based on our analysis and field testing, the average percolation rates for I1 and I2 were 61 and 213 minutes per inch, respectively (see Tables 3 and 4). Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 10 of 60 The asphalt/concrete thicknesses are approximate and should be expected to vary throughout the project site. Prospective contractors should not rely solely on this data for any purpose. Groundwater levels can fluctuate, however, in response to annual and longer-term cycles of precipitation, irrigation, surface drainage and land use, and the development and drainage of transient, perched water conditions. Within the Phase 3 area, groundwater levels will fluctuate with the water level in the drainage ditch. ENGINEERING SEISMICITY According to the 2009 International Building Code® (Section 1613 Earthquake Loads), “Every structure, and portion thereof, including nonstructural components that are permanently attached to structures and their supports and attachments, shall be designed and constructed to resist the effects of earthquake motions in accordance with ASCE 7, excluding Chapter 14 and Appendix 11A. The seismic design category for a structure is permitted to be determined in accordance with Section 1613 (2006/2009 IBC) or ASCE 7.” Exceptions to this are further noted in Section 1613. Utilizing the USGS’s Earthquake Ground Motion Tool v.5.0.9a and site latitude/longitude coordinates of 40.543527 and –105.074088 (obtained from Google Earth) respectively, the project area is indicated to possess an SDS value of 0.238 and an SD1 value of 0.090. Per 2009 IBC, Section 1613.5.2 Site class definitions, “Based on the site soil properties, the site shall be classified as Site Class A, B, C, D, E or F in accordance with Table 1613.5.2. When the soil properties are not known in sufficient detail to determine the site class, Site Class D shall be used unless the building official or geotechnical data determines that Site Class E or F soil is likely to be present at the site”. Zonge conducted a geophysical investigation to determine the one-dimensional shear wave velocity structure to a depth of at least 100 feet. The testing utilized a seismic refraction microtremor (ReMi) soundings to measure Vs100 values along three lines. This analysis is attached at the end of this report. From Zonge’s data, an average shear wave velocity of 1,567 ft/sec was determined, which classifies the site as Seismic Site Class C, according to 2009 IBC and the City and County of Denver IBC Amendments. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 11 of 60 The largest recorded earthquake (estimated magnitude 6.2 to 6.6) in Colorado occurred in November 1882. While the specific location of this earthquake is very uncertain, it is postulated to have occurred in the Front Range near Rocky Mountain National Park. The most recent significant seismic movements associated with the historically active Rocky Mountain Arsenal Fault (Commerce City, Colorado) occurred in the 1960s, generating earthquakes up to magnitude 5.5. Since the early 1960s, numerous earthquakes with magnitudes up to approximately 5, with the majority possessing magnitudes of 2 to 4, have been experienced within the State. Earthquakes ranging in magnitude from 3.7 (Craig, Colorado) to 3.9 (Eads, Colorado and Trinidad, Colorado) occurred during the time period between July 2009 and August 2009. On August 23, 2011, a 5.3 magnitude earthquake occurred 9 miles west-southwest of Trinidad, Colorado. Earthquakes with similar magnitudes, and potentially greater, are anticipated to continue by the USGS, throughout the State. Therefore, the risk of damaging, earthquake-induced ground motions at the site is considered to be relatively low given the low, previously recorded, seismic magnitudes. Furthermore, based on the subsurface conditions at the site and the risks associated with this nearest fault, the risk of liquefaction of the site soils is considered low. DRAINAGE IMPROVEMENTS Based on information provided by the project team, provided grading information, and our site visits, an existing drainage ditch traverses the southwestern portion of the project site, specifically within Blocks 4 through 6 (Phase 3) and may be filled and relocated prior to construction. Based on provided grading plans, material fills ranging from 5 to 8 feet will be necessary to fill in this drainage easement. GROUND recommends the entire extent of this drainage area be excavated down to competent, stable materials and observed by the Geotechnical Engineer prior to backfilling commencement. Actual depths of excavation are dependent on the depth of soft “muck” material, vegetation, unsuitable materials, etc., removed within the drainage. Prior to filling this drainage, once at competent, stable materials, the placement of a large drain/pipe surrounded with clean crushed rock on the order of 10 feet wide or to the lateral extents of the drainage and wrapped with a separating geotextile should be installed. Actual depths of excavation are dependent on the depth of soft material removed within the drainage. To further define the extent of soft material to be removed Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 12 of 60 in the drainage, we recommend that test pits be excavated perpendicular to the drainage. Our office should be provided with final site grading plans to develop more detail recommendations regarding this drainage. In areas where the existing drainage will be backfilled and re-routed to a different location, the existing drainage gravel drain must be daylighted or provide with a positive means of gravity drainage away from the project. Contractors should be cognizant in areas consisting of this existing drainage to prevent damage of the large drain/pipe. Where fill is to be placed within the drainage, the slopes should be benched. The benches shall be cut 3 feet horizontally into the existing slope to create a stepped bench condition. Where groundwater seepage is encountered or anticipated, the benches should be provided with back drains. In such cases, the bench surface should be sloped back toward the drain. The vertical step should not exceed 2 feet between benches. To achieve adequate compaction near the outer faces of fill slopes, it may be beneficial to over-build the slopes and trim them back. Settlements will occur in filled ground, typically on the order of 1 to 2 percent of the fill depth. For a 5-foot fill, this corresponds to settlements on the order of 1 inch, without imposition of loads. If fill placement is performed properly and is tightly controlled, in GROUND’s experience the majority of that settlement will take place during earthwork construction. To further reduce potential settlements, GROUND recommends fill placement should be held to a greater compaction, such as 100 percent of the standard Proctor or 98 percent of the modified Proctor. Please refer to the Project Earthwork section of this report for additional recommendations for fill placement. Additionally, we understand that this drainage will be re-located to the west along South College Avenue. During construction of the buildings in this area, the new drainage should be evaluated for seepage into the surrounding soils. GROUND recommends the project Civil Engineer evaluate the future potential for any drainage to convey water after being in-filled as this could influence long-term, post-construction settlements and associated movements. Our office can assist with this, but the services of a hydrologist may be required. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 13 of 60 FOUNDATION AND FLOOR SYSTEM OVERVIEW Below is a summary of the foundation/floor system recommendations for each Phase. In the event future owners have specific requirements for building design (such as the Cinema, etc.), we should be notified and provided with these requirements as the recommendations provided herein may need to be re-evaluated. Phase 1 – Blocks 7 to 10 According to provided information, it appears that construction of Blocks 7 through 10 will necessitate material fills ranging from approximately 2 to 5 feet. According to our field and laboratory analysis and the nature of the proposed construction, it is GROUND’s opinion the materials encountered in our exploration are generally suitable to support a shallow foundation system consisting of spread footings with a slab-on- grade floor system provided that the upper 12 inches below the footings and slabs be scarified, moisture-conditioned, and re-compacted in accordance with the Project Earthwork section of our report. Utilizing this option as well as other applicable recommendations provided in this report, GROUND anticipates potential movements on the order of 1 inch. Phase 1 – Existing Mall Renovation/Reconstruction Reconstruction/renovation of the existing mall structure appears to necessitate material cuts and fills up to approximately 3 feet. According to our field and laboratory analysis and the nature of the proposed reconstruction, it is GROUND’s opinion the materials encountered are generally suitable to support the proposed renovations/additions on shallow foundation systems and slab-on-grade floor systems (if applicable). The contractor should take precaution to not undermine adjacent structural elements during building addition/renovation construction and temporary shoring may be required. To use these recommendations, the Owner must accept the risk of post-construction foundation movement associated with shallow foundation systems placed on the on-site soils. Utilizing the above recommendations as well as other recommendations in this report, GROUND estimates potential movements may be on the order of 1 inch. Actual movements may be more or less. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 14 of 60 Additionally, design with respect to the connection between the new additions/renovations and the existing mall structure should account for the potential of differential movement. If the recommendations herein are followed, we anticipate potential movements relating to differential settlement to be approximately 1 inch. Phase 1 – Restaurant (Rest.) 1 to 4 The proposed restaurants on the south side of the existing mall structure will necessitate material cuts up to approximately 1 foot and fills up to approximately 4 feet. Additionally, these structures are located within and beyond the extents of the existing facility resulting in the demolition of a portion of the existing mall structure in order to accommodate future construction. As previously stated, we assume that no basement level is associated with the existing mall structure. Therefore, it is GROUND’s opinion that Rest. 1 through 4 may be founded on a shallow foundation system consisting of spread footings with a slab-on-grade floor system provided that a uniform layer of properly moisture-density treated materials is placed beneath the entire building footprint(s) of the proposed structures to reduce differential settlements between footings or along continuous footings as well as across floor slabs. The depth of this layer should be determined by the greatest depth of excavation necessary during site demolition. Following the construction of the fill prism, a shallow foundation system consisting of spread footings with a slab-on-grade floor system may be constructed for the proposed building(s). Precaution should be taken adjacent to the mall structure that will remain intact. Utilizing this option as well as other applicable recommendations provided in this report, GROUND anticipates potential movements on the order of 1 inch. Phase 1 – Parking Garage As previously stated, we understand that maximum anticipated column loads for the parking garage will range from approximately 1,000 to 1,250 kips. Additionally, according to the results of our field and laboratory testing program, variable conditions (low density values/blow counts, moisture contents, etc.) exist within the subsurface materials. These conditions typically result in a lower allowable soil bearing pressure and require subgrade reconditioning. These conditions appear to suggest that the use of shallow foundations for the parking garage may be impractical because of the potential large footing sizes and related costs. Therefore, to accommodate the Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 15 of 60 anticipated column loads, the results of our field, laboratory, and office studies, as well as our understanding of the project, it is GROUND’s opinion that the foundation system should consist of a deep foundation, such as straight-shaft drilled piers advanced into the underlying bedrock. Additionally, entryways and other attached appurtenances should ideally be founded on piers the same as the main structure, to reduce the potential of differential movement. Utilizing this option as well as other applicable recommendations provided in this report, GROUND anticipates potential post- construction foundation movements of approximately ½-inch. Even though a structural floor system would provide the least risk of post-construction slab movement, we understand that these floor systems are often not practical for parking garages. According to provided grading plans, material cuts up to approximately 2 feet and material fills up to approximately 4 feet are anticipated for the proposed parking garage. Therefore, it is our opinion that a slab-on-grade floor system may be utilized provided that the upper 12 inches below the slab be scarified, moisture- conditioned, and re-compacted in accordance with the Project Earthwork section of our report. Utilizing this option as well as other applicable recommendations provided in this report, GROUND anticipates potential slab movements on the order of 1 inch. Phase 1 – Cinema As previously stated, we understand that maximum anticipated column loads for the proposed cinema will be approximately 100 kips. For the least risk of post construction movement, a deep foundation, such as straight-shaft drilled piers advanced into the underlying bedrock and providing them with a structural floor system would be utilized. Utilizing this option as well as other applicable recommendations provided in this report, GROUND anticipates potential post-construction foundation movements of approximately ½-inch. Additionally, but not equal in anticipated building performance (post-construction movements) the cinema structure could be founded on a shallow foundation system consisting of spread footings with a slab-on-grade floor system. A small portion of the cinema structure may be located within and beyond the extents of the existing mall structure. In the event this is the case, a uniform layer of properly moisture-density treated materials should be placed beneath the entire building footprint(s) of the Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 16 of 60 proposed structures to reduce differential settlements between footings or along continuous footings as well as across floor slabs. The depth of this layer should be determined by the greatest depth of excavation necessary during site demolition. In the event the cinema structure is not located within a portion of the existing mall structure footprint, prior to placement of concrete, the upper 12 inches beneath footings and slabs should be scarified, moisture-conditioned, and re-compacted in accordance the Project Earthwork section of our report. Precaution should be taken adjacent to the mall structure that will remain intact. Utilizing this option as well as other applicable recommendations provided in this report, GROUND anticipates potential movements on the order of 1 inch. Phase 2 - Blocks 1 to 3 The proposed retail buildings within the northwestern portion of the project site will consist of material fills up to approximately 4 feet. Additionally, some of these structures are located within and beyond the extents of the existing structures. As previously stated, we assume that no basement level is associated with the existing structures. Therefore, it is GROUND’s opinion that following demolition and backfill of the existing structures, Blocks 1 to 3 may be founded on a shallow foundation system consisting of spread footings with a slab-on-grade floor system provided that a uniform layer of properly moisture-density treated materials is placed beneath the entire building footprint(s) of the proposed structures to reduce differential settlements between footings or along continuous footings as well as across floor slabs. Following the construction of the fill prism, a shallow foundation system consisting of spread footings with a slab-on- grade floor system may be constructed for the proposed building(s). Utilizing this option as well as other applicable recommendations provided in this report, GROUND anticipates potential movements on the order of 1 inch. In the event an existing structure is not located within the new building footprint (Block 2), it is our opinion that the upper 12 inches beneath footings and slabs be scarified, moisture-conditioned, and re-compacted in accordance the Project Earthwork section of our report. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 17 of 60 Phase 3 - Blocks 4 to 6 As stated above, the existing drainage easement will be filled in to accommodate building construction of Blocks 4 to 6. Additionally, some of these structures are located within and beyond the extents of the existing structures. Therefore, following demolition and fill placement of the drainage and building excavation, in order to reduce the post- construction movement potential of the site soils, GROUND recommends a uniform layer of properly moisture-density treated materials is placed beneath the entire building footprint(s) of the proposed structures to reduce differential settlements between footings or along continuous footings as well as across floor slabs. The depth of this layer should be determined by the greatest depth of excavation necessary during site demolition or drainage or fill placement of the drainage. Following the construction of the fill prism, a shallow foundation system consisting of spread footings with a slab-on-grade floor system may be constructed for the proposed building(s). Utilizing this option as well as other applicable recommendations provided in this report, GROUND anticipates potential movements on the order of 1 inch. Other Foundation/Floor System Considerations Overexcavation layers ideally should extend laterally at least 5 feet beyond the building beneath any building appurtenances including entryways, patios, courtyards, etc. Fill materials may consist of moisture-density treated on-site materials or approved import materials. These materials should be placed in accordance with the recommendations provided in the Project Earthwork section of our report. Existing foundation elements should be entirely removed and the resultant excavation properly backfilled in accordance with the Project Earthwork section of this report. Additionally, if portions of the existing foundations are below grade, i.e. mechanical rooms, grease traps, etc., the excavation and backfill should consist of the entire building footprint to the depth of the lowest foundation element. Below is a summary of the recommended foundation/floor systems for the locations indicated above. Please refer to the above sections for a detailed explanation of these systems. As discussed in the sections above, due to the demolition and backfill excavation of the existing buildings or drainage easement, Rest. 1 to 4, Blocks 1 to 3, a small portion of the cinema, and Blocks 4 to 6 should include a uniform fill prism Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 18 of 60 (laterally consistent) beneath the structures. Greater depths are required if below grade levels are encountered during construction. Location Foundation/Floor Type Overexcavation beneath Shallow Foundation/Slab- on-Grade* Phase 1 - Block 7 to 10 Spread Footings/Slab-on- Grade 12-inch Scarification beneath Footings and Slabs Phase 1 – Existing Mall Renovation/Reconstruction Spread Footings/Slab-on- Grade (if applicable) Undisturbed On-site Material/12-inch Scarification Phase 1 – Restaurant (Rest. 1 to 4) Spread Footings/Slab-on- Grade Uniform Fill Prism Phase 1 – Parking Garage Drilled Piers / Slab-on- Grade Floors 12-inch Scarification beneath Slabs Phase 1 – Cinema Drilled Piers or Spread Footings/ Slab-on-Grade Floors Uniform Fill Prism or 12- inch Scarification beneath Footings and Slabs Phase 2 – Blocks 1 to 3 Spread Footings/Slab-on- Grade Uniform Fill Prism or 12- inch Scarification beneath Footings and Slabs Phase 3 – Blocks 4 to 6 Spread Footings/Slab-on- Grade Uniform Fill Prism *To be performed prior to placing any new fill material. FOUNDATION SYSTEM Spread Footings The design and construction criteria presented below should be observed for a spread footing foundation system. The construction details should be considered when preparing project documents. The precautions and recommendations provided below will not prevent movement of the footings if the underlying materials are subjected to alternate wetting and drying cycles. However, the recommended measures will tend to make the movement more uniform, and reduce resultant damage if such movement occurs. Based on the assumption of effective surface and subsurface drainage away from the building as well as the recommendations presented herein, we anticipate the Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 19 of 60 following system would result in movement potentials on the order of 1 inch. Movement estimates are difficult to predict and actual movements may be more or less. 1) Footings bearing on properly prepared materials may be designed for an allowable soil bearing pressure (Q) of 2,000 psf. As stated, most of the buildings with the exception of renovation areas should include construction of a uniform fill prism or be placed on a minimum of 12 inches of properly moisture-density treated site generated materials (see previous). Based on this allowable bearing capacity, we anticipate post-construction settlements to be on the order of 1 inch. Fills should be constructed in accordance with the recommendations provided in the Project Earthwork section of this report. Increased bearing capacities can be provided with additional overexcavation and compaction efforts. Our office should be contacted in the event these are desired. 2) The recommended allowable bearing pressure was based on an assumption of drained conditions and footing widths of 4 feet or less. If foundation materials are subjected to increase fluctuations in moisture content, the effective bearing capacity will be reduced and greater post-construction movements than those estimated above may result. We should be contacted if planned footing widths exceed 4 feet. 3) In the event the Cinema is constructed on spread footings, the above soil bearing pressure could be utilized for a footing dimension of 7 feet x 7 feet (based on a maximum column load of approximately 100 kips). Based on the above bearing pressure, total settlements may be on the order of 1 inch. In the event the dimension and shape of the footings differ from those utilizing in our analysis, settlements greater than 1 inch may occur. 4) Footing excavation bottoms may expose loose, organic or otherwise deleterious materials, including debris. Firm materials may be disturbed by the excavation process. All such unsuitable materials should be excavated and replaced with properly compacted fill. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 20 of 60 5) In order to reduce differential settlements between footings or along continuous footings, footing loads should be as uniform as possible. Differentially loaded footings will settle differentially. Similarly, differential fill thicknesses beneath footings will result in increased differential settlements. 6) Spread footings should have a minimum footing dimension of 14 or more inches. Actual footing dimensions, however, should be determined by the Structural Engineer, based on the design loads. 7) Footings should be provided with adequate soil cover above their bearing elevation for frost protection. Footings should be placed at a bearing elevation 3 or more feet below the lowest adjacent exterior finish grades. 8) Continuous foundation walls should be reinforced top and bottom to span an unsupported length of at least 10 feet. 9) The lateral resistance of spread footings will be developed as sliding resistance of the footing bottoms on the foundation materials and by passive soil pressure against the sides of the footings. Sliding friction at the bottom of footings may be taken as 0.33 times the vertical dead load. 10) Compacted fill placed against the sides of the footings should be compacted to at least 95 percent relative compaction in accordance with the recommendations in the Project Earthwork section of this report. 11) Care should be taken when excavating the foundations to avoid disturbing the supporting materials. Hand excavation or careful backhoe soil removal may be required in excavating the last few inches. 12) Foundation soils may be disturbed or deform excessively under the wheel loads of heavy construction vehicles as the excavations approach footing levels. Construction equipment should be as light as possible to limit development of this condition. The use of track-mounted vehicles is recommended since they exert lower contact pressures. The movement of vehicles over proposed foundation areas should be restricted. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 21 of 60 13) All footing areas should be compacted with a vibratory plate compactor prior to placement of concrete. 14) The Civil Design Engineer(s) and contractor should evaluate the possible sources of water in the project area over the life of the structure, and provide a design/construction agenda that ensures not to allow moisture to infiltrate the foundation/structure supporting materials before, during, or after construction. Drilled Piers The design criteria presented below should be observed for a straight-shaft pier foundation system. The construction details should be considered when preparing project documents. 1) Piers may be designed for an allowable end bearing pressure of 30,000 psf and skin friction values of 3,000 psf for the portion of the pier penetrating comparably unweathered bedrock. This skin friction value assumes the installation of shear rings. The upper 1 foot of bedrock penetration should be ignored in all load calculations. 2) Piers also should be designed for a minimum dead load pressure of 5,000 psf based on pier end area only. If the minimum dead load requirement cannot be achieved and the piers are spaced as far apart as is practical, the pier length should be extended beyond the minimum length to make up the dead load deficit. This can be accomplished by assuming the skin friction located in the extended zone acts in the direction to resist uplift. This value may be increased by 1/3 for transient loads such as wind or seismic loading. 3) Piers should penetrate at least 10 feet into comparably unweathered bedrock and have a minimum length of 30 feet. Based on the depth to bedrock encountered in the test holes, piers approximately 30 to 34 feet in length should meet these minimum criteria. Both criteria for minimum pier length and minimum bedrock penetration should be met. However, the actual pier lengths should be based on the specific design loads, the requirement for minimum dead load pressure, etc., as determined by the Structural Engineer, as well as the actual conditions encountered in the field at each pier location during installation. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 22 of 60 4) A minimum pier diameter of 18 inches is recommended to facilitate proper cleaning and observation of the pier hole. Larger pier diameters than the minimum may be needed to accommodate the anticipated significant loads, as well to comply with diameter to length ratios recommend by the structural engineer. 5) Piers may be designed to resist lateral loads assuming a soil horizontal modulus of 90 tcf in overburden sands, gravels, and clays and 400 tcf in competent sandstone and claystone bedrock. 6) Bedrock penetration in pier holes should be roughened artificially to assist the development of peripheral shear between the pier and bedrock. Artificially roughening of pier holes should consist of installing shear rings 3 inches high and 2 inches deep in the lower 10 feet of each hole. The shear rings should be installed 18 inches on centers. The specifications should allow the Geotechnical Engineer to waive the requirement for shear rings depending on the conditions actually encountered in individual pier holes, however. 7) Groups of piers required to support concentrated loads will require an appropriate reduction of the estimated bearing capacity based on the effective envelope area of the pier group. Reduction of axial capacity can be avoided by spacing piers at least 3 diameters center to center. Pier groups spaced less than 3 diameters center to center should be studied on an individual basis to determine the appropriate axial capacity reductions(s). 8) Piers should be reinforced for their full length to resist the ultimate tensile load created by the on-site materials. Adequate reinforcement should be designed to resist the deficit between the design dead load on the pier and the uplift pressures acting on the pier perimeter in the upper 15 feet of material penetrated by the pier. Tension may be estimated on the basis of an uplift pressure of 750 psf in the upper 15 feet of material penetrated by the pier, and on the surface area of the pier. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 23 of 60 9) Based on the results of our field exploration, laboratory testing, and our experience with similar, properly constructed, drilled pier foundations, we estimate pier settlement will be low, on the order of ½-inch to mobilize skin friction. The settlement of closely spaced piers will be larger and should be studied under an individual basis. 10) A minimum void form of 6 inches should be provided beneath grade beams to reduce the potential of the swelling soil and bedrock from exerting uplift forces on the grade beams, as well as to concentrate pier loadings. The same void should also be provided beneath necessary pier caps. 11) Groundwater was encountered in the test holes at depths ranging from 11 to 27 feet below existing grade at the time of drilling and at depths ranging from 12 to 19 feet across the project site when measured 7 and 14 days later. Therefore, the use of casing may be required for pier installation. The requirements for casing can sometimes be reduced by placing concrete immediately upon cleaning and observing the pier hole. In no case should concrete be placed in more than 3 inches of water, unless placed through an approved “tremie” method. 12) Pier holes should be properly cleaned prior to placement of concrete. 13) Concrete utilized in the piers should be a fluid mix with sufficient slump so that it will fill the void between reinforcing steel and the pier hole wall. We recommend the concrete have a minimum slump in the range of 5 to 7 inches. Concrete should be placed by an approved “tremie”-type method or other methods such as the utilization of a long steel pipe or “elephant trunk” to reduce mix segregation. The “tremie” should be extended down into the center of the drilled pier shaft in order to provide a clear pathway through the reinforcement cage. A centering chute that extends to shallow depths may not be sufficient. 14) Concrete should be placed in piers the same day they are drilled. Failure to place concrete the day of drilling will normally result in a requirement for additional bedrock penetration. The presence of groundwater or caving soils at the time of pier installation may require that concrete be placed immediately after the pier hole drilling is completed. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 24 of 60 15) The Contractor should take care to prevent enlargement of the excavation at the tops of piers, which could result in mushrooming of the pier top. Mushrooming of pier tops can increase uplift pressures on the piers. 16) The bedrock beneath the site is hard to very hard and relatively resistant. These conditions should be anticipated during construction. The pier drilling Contractor should mobilize equipment of sufficient size and operating capability to achieve the required penetration into the bedrock. GROUND recommends a high-torque, commercial rig be used. If refusal is encountered in these materials, the Geotechnical Engineer should be retained to evaluate the conditions to establish that true refusal has been met with adequate drilling equipment. FLOOR SYSTEM Slab-on-Grade The following measures are recommended to reduce damage, which may result from movement of the slab subgrade material. These measures will not eliminate potential movements. If slab-on-grade construction is used in accordance with the following criteria, as well as other applicable recommendations contained in this report, we estimate that potential slab movements may be on the order of 1 inch. The actual magnitude of movement is difficult to estimate and may be more or less. 1) Floor slabs should be placed on properly prepared materials. As stated, construction of a uniform fill prism (determined by the greatest depth of excavation necessary during building demolition) or scarified, moisture- conditioned, and re-compacted to a depth of at least 12 inches below the slabs (if existing foundation elements are not present within proposed footprint) will be required. These materials should be placed in accordance with the recommendations in the Project Earthwork section of our report. 2) The prepared surface on which the floor slabs will be cast should be observed by the Geotechnical Engineer prior to placement of reinforcement. Exposed loose, soft, or otherwise unsuitable materials should be excavated and replaced with properly compacted fill, placed in accordance with the recommendations in the Project Earthwork section of this report. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 25 of 60 3) Floor slabs should be separated from all bearing walls and columns with slip joints, which allow unrestrained vertical movement. Joints should be observed periodically, particularly during the first several years after construction. Slab movement can cause previously free-slipping joints to bind. Measures should be taken to assure that slab isolation is maintained in order to reduce the likelihood of damage to walls and other interior improvements. 4) Interior partitions resting on floor slabs should be provided with slip joints so that if the slabs move, the movement cannot be transmitted to the upper structure. This detail is also important for wallboards and door frames. A slip joint which will allow sufficient vertical movement is recommended. If slip joints are placed at the tops of walls, in the event that the floor slabs move, it is likely that the wall will show signs of distress, especially where the floors meet the exterior wall. 5) Concrete slabs-on-grade should be placed on properly prepared subgrade. They should also be constructed and cured according to applicable standards and be provided with properly designed and constructed control joints. The design and construction of such joints should account for cracking as a result of shrinkage, tension, and loading; curling; as well as proposed slab use. Joint layout based on the slab design may require more frequent, additional, or deeper joints, and should also be based on the ultimate use and configuration of the slabs. Areas where slabs consist of interior corners or curves (at column blockouts or around corners) or where slabs have high length to width ratios, high degree of slopes, thickness transitions, high traffic loads, or other unique features should be carefully considered. The improper placement or construction of control joints will increase the potential for slab cracking. ACI, AASHTO, and other industry groups provide many guidelines for proper design and construction of concrete slabs on grade and the associated jointing. 6) Floor slabs should be adequately reinforced. Recommendations based on structural considerations for slab thickness, jointing, and steel reinforcement in floor slabs should be developed by the Structural Engineer. Placement of slab reinforcement continuously through the control joint alignments will tend to Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 26 of 60 increase the effective size of concrete panels and reduce the effectiveness of control joints. 7) All plumbing lines should be carefully tested before operation. Where plumbing lines enter through the floor, a positive bond break should be provided. Flexible connections allowing sufficient vertical movement should be provided for slab- bearing mechanical equipment. 8) Moisture can be introduced into a slab subgrade during construction and additional moisture will be released from the slab concrete as it cures. GROUND recommends placement of a properly compacted layer of free-draining gravel, 4 or more inches in thickness, beneath the slabs. This layer will help distribute floor slab loadings, ease construction, reduce capillary moisture rise and aid in drainage. The free-draining gravel should contain less than 5 percent material passing the No. 200 Sieve, more than 50 percent retained on the No. 4 Sieve, and a maximum particle size of 2 inches. The capillary break and the drainage space provided by the gravel layer also may reduce the potential for excessive water vapor fluxes from the slab after construction as mix water is released from the concrete. A vapor barrier beneath a building floor slab can be beneficial with regard to reducing exterior moisture moving into the building, through the slab, but can retard downward drainage of construction moisture. Uneven moisture release can result in slab curling. Elevated vapor fluxes can be detrimental to the adhesion and performance of many floor coverings and may exceed various flooring manufacturers’ usage criteria. Per the 2006 ACI Location Guideline, a vapor barrier is required under concrete floors when that floor is to receive moisture-sensitive floor covering and/or adhesives, or the room above that floor has humidity control. Therefore, in light of the several, potentially conflicting effects of the use of vapor barriers, the Owner and the Architect and/or Flooring Contractor should weigh the performance of the slab and appropriate flooring products in light of the intended building use, etc., during the floor system design process and the Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 27 of 60 selection of flooring materials. Use of a vapor barrier may be appropriate for some buildings and not for others. In the event a vapor barrier is utilized, it should consist of a minimum 15 mil thickness, extruded polyolefin plastic (no recycled content or woven materials), maintain a permeance less than 0.01 perms per ASTM E-96 or ASTM F-1249, and comply with ASTM E-1745 (Class “A”). Vapor barriers should be installed in accordance with ASTM E-1643. Polyethylene (“poly”) sheeting (even if 15 mils in thickness which polyethylene sheeting commonly is not) does not meet the ASTM E-1745 criteria and is not recommended for use as vapor barrier material. It can be easily torn and/or punctured, does not possess necessary tensile strength, gets brittle, tends to decompose over time, and has a relatively high permeance. Slab movements are directly related to the increases in moisture contents to the underlying soils after construction is completed. The precautions and recommendations itemized above will not prevent the movement of floor slabs if the underlying materials are subjected to excessive moisture. However, these steps will reduce the damage if such movement occurs. MECHANICAL ROOMS/MECHANICAL PADS Often, slab-bearing mechanical rooms/mechanical equipment are incorporated into projects. Our experience indicates these are located as partially below-grade or adjacent to the exterior of a structure. GROUND recommends these elements be founded on the same type of foundation systems as the main structure. Furthermore, mechanical connections must allow for potential differential movements. EXTERIOR FLATWORK Proper design, drainage, construction and maintenance of the areas between individual buildings and parking/driveway areas are critical to the satisfactory performance of the project. Sidewalks, entranceway slabs and roofs, fountains, raised planters and other highly visible improvements commonly are installed within these zones, and distress in or near these improvements is common. Commonly, soil preparation in these areas Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 28 of 60 receives little attention because they fall between the building and pavement (which are typically built with heavy equipment). Subsequent landscaping and hardscape installation often is performed by multiple sub-contractors with light or hand equipment, and over-excavation / soil processing is not performed. Therefore, GROUND recommends that the design team, contractor, and pertinent subcontractors take particular care with regard to proper subgrade preparation around the structure exteriors. Similar to slab-on-grade floors, exterior flatwork and other hardscaping placed on the soils encountered on-site may experience post-construction movements due to volume change of the subsurface soils and the relatively light loads that they impose. Both vertical and lateral soil movements can be anticipated as the soils experience volume change as the moisture content varies. Distress to rigid hardscaping likely will result. The following measures will help to reduce damages to these improvements. Ideally, subgrade soils beneath project sidewalks, paved entryways and patios, masonry planters and short, decorative walls, and other hardscaping should be placed on the same amount of processed soil as those recommended for the floor slabs, or greater. Provided the owner understands the risks identified above, we believe that subgrade under exterior flatwork or other (non-building) site improvements could be scarified to a minimum depth of 12 inches. This should occur prior to placing any additional fill required to achieve finished design grades. This processing depth will not eliminate potential movements. The excavated soil should be replaced as properly moisture- conditioned and compacted fill as outlined in the Project Earthwork section of this report. As stated above, greater depths of moisture-density conditioning of the subgrade soils beyond the above minimum will improve hardscape performance. Movement will occur, some of which could be significant, especially if sufficient surface drainage is not maintained. Prior to placement of flatwork, a proof roll should be performed to identify areas that exhibit instability and deflection. The soils in these areas should be removed and replaced with properly compacted fill or stabilized. Flatwork should be provided with effective control joints. Increasing the frequency of joints may improve performance. ACI recommendations should be followed regarding construction and/or control joints. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 29 of 60 In no case should exterior flatwork extend to under any portion of the building where there is less than several inches of clearance between the flatwork and any element of the building. Exterior flatwork in contact with brick, rock facades, or any other element of the building can cause damage to the structure if the flatwork experiences movements. As discussed in the Surface Drainage section of this report, proper drainage also should be maintained after completion of the project, and re-established as necessary. In no case should water be allowed to pond on or near any of the site improvements or a reduction in performance should be anticipated. Water Features Locations of water features planned with the project site should be provided to GROUND in order to evaluate the proximity to structures and the necessity of underdrains and/or liners. Concrete Scaling Climatic conditions in the project area including relatively low humidity, large temperature changes and repeated freeze – thaw cycles, make it likely that project sidewalks and other exterior concrete will experience surficial scaling or spalling. The likelihood of concrete scaling can be increased by poor workmanship during construction, such as ‘over-finishing’ the surfaces. In addition, the use of de-icing salts on exterior concrete flatwork, particularly during the first winter after construction, will increase the likelihood of scaling. Even use of de-icing salts on nearby roadways, from where vehicle traffic can transfer them to newly placed concrete, can be sufficient to induce scaling. Typical quality control / quality assurance tests that are performed during construction for concrete strength, air content, etc., do not provide information with regard to the properties and conditions that give rise to scaling. We understand that some municipalities require removal and replacement of concrete that exhibits scaling, even if the material was within specification and placed correctly. The contractor should be aware of the local requirements and be prepared to take measures to reduce the potential for scaling and/or replace concrete that scales. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 30 of 60 In GROUND’s experience the measures below can be beneficial for reducing the likelihood of concrete scaling. It must be understood, however, that because of the other factors involved, including weather conditions and workmanship, surface damage to concrete can develop, even where all of these measures were followed. 1) Maintaining a maximum water/cement ratio of 0.45 by weight for exterior concrete mixes. 2) Include Type F fly ash in exterior concrete mixes as 20 percent of the cementitious material. 3) Specify a minimum, 28-day, compressive strength of 4,500 psi for all exterior concrete. 4) Including ‘fibermesh’ in the concrete mix also may be beneficial for reducing surficial scaling. 5) Cure the concrete effectively at uniform temperature and humidity. This commonly will require fogging, blanketing and/or tenting, depending on the weather conditions. As long as 3 to 4 weeks of curing may be required, and possibly more. 6) Avoid placement of concrete during cold weather so that it is not exposed to freeze-thaw cycling before it is fully cured. 7) Avoid the use of de-icing salts on given reaches of flatwork through the first winter after construction. We understand that commonly it may not be practical to implement some of these measures for reducing scaling due to safety considerations, project scheduling, etc. In such cases, additional costs for flatwork maintenance or reconstruction should be incorporated into project budgets. WATER-SOLUBLE SULFATES The concentrations of water-soluble sulfates measured in selected samples retrieved from the test holes ranged from less than the detectable limit of 0.01 percent to 0.04 Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 31 of 60 percent by weight (See Table 2). Such concentrations of water-soluble sulfates represent a negligible degree of sulfate attack on concrete exposed to these materials. Degrees of attack are based on the scale of 'negligible,' 'moderate,' 'severe' and 'very severe' as described in the “Design and Control of Concrete Mixtures,” published by the Portland Cement Association (PCA). The Colorado Department of Transportation (CDOT) utilizes a corresponding scale with 4 classes of severity of sulfate exposure (Class 0 to Class 3) as described in the published table below. Requirements to Protect Against Damage to Concrete by Sulfate Attack from External Sources of Sulfate Severity of sulfate exposure Water-soluble sulfate (SO4) in dry soil, percent, Sulfate (SO4) in water, ppm Water cementitious ratio, maximum Cementitious material requirements Class 0 0.00 to 0.10 0 to 150 0.45 Class 0 Class 1 0.11 to 0.20 151 to 1500 0.45 Class 1 Class 2 0.21 to 2.00 1501 to 10,000 0.45 Class 2 Class 3 2.01 or greater 10,001 or greater 0.40 Class 3 Based on these data GROUND, makes no recommendation for use of a special, sulfate- resistant cement in project concrete. SOIL CORROSIVITY The degree of risk for corrosion of metals in soils commonly is considered to be in two categories: corrosion in undisturbed soils and corrosion in disturbed soils. The potential for corrosion in undisturbed soil is generally low, regardless of soil types and conditions, because it is limited by the amount of oxygen that is available to create an electrolytic cell. In disturbed soils, the potential for corrosion typically is higher, but is strongly affected by soil conditions for a variety of reasons but primarily soil chemistry. A corrosivity analysis was performed to provide a general assessment of the potential for corrosion of ferrous metals installed in contact with earth materials at the site, based on the conditions existing at the time of GROUND’s evaluation. Soil chemistry and physical property data including pH, oxidation-reduction (redox) potential, sulfides, and moisture content were obtained. Test results are summarized on Table 2. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 32 of 60 Soil Resistivity In order to assess the “worst case” for mitigation planning, samples of materials retrieved from the test holes were tested for resistivity in the in the laboratory, after being saturated with water, rather than in the field. Resistivity also varies inversely with temperature. Therefore, the laboratory measurements were made at a controlled temperature. Measurements of electrical resistivity indicated values ranging from approximately 2,252 to 14,594 ohm-centimeters in samples of retrieved soil. The following table presents the relationship between resistivity and a qualitative corrosivity rating2: Corrosivity Ratings Based on Soil Resistivity Soil Resistivity (ohm-cm) Corrosivity Rating >20,000 Essentially non-corrosive 10,000 – 20,000 Mildly corrosive 5,000 – 10,000 Moderately corrosive 3,000 – 5,000 Corrosive 1,000 – 3,000 Highly corrosive <1,000 Extremely corrosive pH Where pH is less than 4.0, soil serves as an electrolyte; the pH range of about 6.5 to 7.5 indicates soil conditions that are optimum for sulfate reduction. In the pH range above 8.5, soils are generally high in dissolved salts, yielding a low soil resistivity3. Testing indicated pH values ranging from approximately 8.2 to 9.0. The American Water Works Association (AWWA) has developed a point system scale used to predict corrosivity. The scale is intended for protection of ductile iron pipe but is valuable for project steel selection. When the scale equals 10 points or higher, protective measures for ductile iron pipe are recommended. The AWWA scale is presented below. The soil characteristics refer to the conditions at and above pipe installation depth. 2 ASM International, 2003, Corrosion: Fundamentals, Testing and Protection, ASM Handbook, Volume 13A. 3 American Water Works Association ANSI/AWWA C105/A21.5-05 Standard Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 33 of 60 Table A.1 Soil-test Evaluation 4 Soil Characteristic / Value Points Resistivity <1,500 ohm-cm ..........................................................................................… 10 1,500 to 1,800 ohm-cm ................................................................……......…. 8 1,800 to 2,100 ohm-cm .............................................................................…. 5 2,100 to 2,500 ohm-cm ...............................................................................… 2 2,500 to 3,000 ohm-cm .................................................................................. 1 >3,000 ohm-cm ................................................................................… 0 pH 0 to 2.0 ............................................................................................................ 5 2.0 to 4.0 ......................................................................................................... 3 4.0 to 6.5 ......................................................................................................... 0 6.5 to 7.5 ......................................................................................................... 0 * 7.5 to 8.5 ......................................................................................................... 0 >8.5 .......................................................................................................... 3 Redox Potential < 0 (negative values) ....................................................................................... 5 0 to +50 mV ................................................................................................…. 4 +50 to +100 mV ............................................................................................… 3½ > +100 mV ............................................................................................... 0 Sulfide Content Positive ........................................................................................................…. 3½ Trace .............................................................................................................… 2 Negative .......................................................................................................…. 0 Moisture Poor drainage, continuously wet ..................................................................…. 2 Fair drainage, generally moist ....................................................................… 1 Good drainage, generally dry ........................................................................ 0 * If sulfides are present and low or negative redox-potential results (< 50 mV) are obtained, add three points for this range. We anticipate that drainage at the site after construction will be good. Nevertheless, based on the values obtained for the soil parameters, the overburden soils/bedrock appear(s) to comprise a corrosive environment for metals. If additional information or recommendations are needed regarding soil corrosivity, GROUND recommends contacting the American Water Works Association or a 4 American Water Works Association ANSI/AWWA C105/A21.5-05 Standard Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 34 of 60 Corrosion Engineer. It should be noted, however, that changes to the site conditions during construction, such as the import of other soils, or the intended or unintended introduction of off-site water, may alter corrosion potentials significantly. LATERAL EARTH PRESSURES Structures which are laterally supported and can be expected to undergo only a limited amount of deflection should be designed for “at-rest” lateral earth pressures. The cantilevered retaining structures will be designed to deflect sufficiently to mobilize the full active earth pressure condition, and may be designed for “active” lateral earth pressures. “Passive” earth pressures may be applied in front of the structural embedment to resist driving forces. The at-rest, active, and passive earth pressures in terms of equivalent fluid unit weight for the on-site backfill and CDOT Class 1 structure backfill are summarized on the table below. Base friction may be combined with passive earth pressure if the foundation is in a drained condition. The use of passive pressure under a saturated condition is not recommended. The values for the on-site material in the upper 10 feet provided in the table below were approximated utilizing a unit weight of 121 pcf and a phi angle of 26 degrees. The direct shear data obtained from a depth of approximately 4 and 9 feet below grade in Test Holes 28 and 37 along with the properties of the on-site material within the upper 10 feet were utilized to determine the appropriate phi angle for the foundation soils. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 35 of 60 Lateral Earth Pressures (Equivalent Fluid Unit Weights) Material Type Water Condition At-Rest (pcf) Active (pcf) Passive (pcf) Friction Coefficient On-Site Sand and Clay Backfill Drained 68 47 300 0.33 Submerged 95 85 - 0.33 Structure Backfill (CDOT Class 1) Drained 55 35 400 0.45 Submerged 90 80 -- 0.45 If the selected on-site soil meets the criteria for CDOT Class 1 structure backfill as indicated in the Project Earthwork section of this report, the lateral earth pressures for CDOT Class 1 structure backfill as shown on the above table may be used. To realize the lower equivalent fluid unit weight, the selected structure backfill should be placed behind the wall to a minimum distance equal to the retained wall height. The lateral earth pressures recommended above are for a horizontal upper backfill slope. The additional loading of an upward sloping backfill as well as loads from traffic, stockpiled materials, etc., should be included in the wall/shoring design. GROUND can provide the adjusted lateral earth pressures when the additional loading conditions and site grading are clearly defined. Wall Drainage Retaining walls should be provided with drains at the heels of the walls, or with weep holes, or both, to help reduce the development of hydrostatic loads. The underdrain system should consist of perforated PVC drainpipe at least 4 inches in diameter, free-draining gravel, and filter fabric. The free-draining gravel should contain less than 5 percent passing the No. 200 Sieve and more than 50 percent retained on the No. 4 Sieve, and have a maximum particle size of 2 inches. Each drainpipe should be surrounded on the sides and top with 6 or more inches of free-draining gravel. The Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 36 of 60 gravel surrounding the drainpipe and/or the pipe itself should be wrapped with filter fabric to reduce the migration of fines into the drain system. The Civil Engineer should design the actual layout, outlets, and locations. In addition to surrounding the drain pipes with at least 6 inches of free-draining gravel, the gravel should extend upward to within 12 inches of the backfill surface behind the wall or the wall should be backed with a layer of geocomposite drainage medium, e.g., an appropriate MiraDrain® product or equivalent. The gravel or drainage product backing the wall should be in hydraulic connection with the wall heel drain. If gravel is selected, it should be separated from the enclosing soils by a layer of filter fabric to reduce the migration of fines into the drainage system. Damp proofing should be applied to the backside of rigid types of retaining walls. PROJECT EARTHWORK The following information is for private improvements; public roadways or utilities should be constructed in accordance with applicable municipal / agency standards. General Considerations: Site grading should be performed as early as possible in the construction sequence to allow settlement of fills and surcharged ground to be realized to the greatest extent prior to subsequent construction. Prior to earthwork construction, existing structures, asphalt/concrete, vegetation and other deleterious materials should be removed and disposed of off-site. Relic underground utilities should be abandoned in accordance with applicable regulations, removed as necessary, and properly capped. Remnant foundation elements should be entirely removed and the resultant excavation properly backfilled. The Geotechnical Engineer should be contracted to test the excavation backfill during placement. Topsoil present on-site should not be incorporated into ordinary fills. Instead, topsoil should be stockpiled during initial grading operations for placement in areas to be landscaped or for other approved uses. It is not possible to accurately correlate subgrade stability with information derived from site observations made during the geotechnical exploration or subsequent laboratory Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 37 of 60 testing. It is often our experience that when pavements are removed, the pavement subgrade experiences instability when subjected to building construction and/or traffic loading, even when laboratory testing suggests reasonable moisture contents and density. Therefore, it may be necessary to stabilize the majority of the existing subgrade prior to repaving. This may require reprocessing of existing soils or removal and replacement with other site materials or imported soil. Our office should be retained to observe the subgrade condition and stability during the removal process. If additional or more specific information is required, then we suggest removal of several large sections of these existing pavement areas for evaluation prior to design or bidding. Drainage Area: As previously stated, materials within the existing drainage should be excavated and removed to the greatest depth of “muck”/unsuitable materials (rip rap, etc.) encountered during construction. If soft materials are exposed, these materials should be removed as necessary and replaced with suitable materials. Existing Fill Soils: Although not obviously encountered in the test holes, man-made fill may exist on site. Actual contents and composition of the man-made fill materials are not known; therefore, some of the excavated man-made fill materials may not be suitable for replacement as backfill. The Geotechnical Engineer should be retained during site excavations to observe the excavated fill materials and provide recommendations for its suitability for reuse. Use of Existing Native Soils: Overburden soils that are free of trash, organic material, construction debris, and other deleterious materials are suitable, in general, for placement as compacted fill. Organic materials should not be incorporated into project fills. Fragments of rock, cobbles, and inert construction debris (e.g., concrete or asphalt) larger than 3 inches in maximum dimension will require special handling and/or placement to be incorporated into project fills. In general, such materials should be placed as deeply as possible in the project fills. A Geotechnical Engineer should be consulted regarding appropriate recommendations for usage of such materials on a case-by-case basis when such materials have been identified during earthwork. Standard recommendations that likely will be generally applicable can be found in Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 38 of 60 Section 203 of the current CDOT Standard Specifications for Road and Bridge Construction. Sandstone fragments should not exceed 3 inches in largest dimension and siltstone fragments should be reduced to a soil-like mass. Imported Fill Materials: If it is necessary to import material to the site, the imported soils should be free of organic material, and other deleterious materials. Imported material should consist of relatively impervious soils that have less than 50 percent passing the No. 200 Sieve and should have a plasticity index of less than 15. Representative samples of the materials proposed for import should be tested and approved by the Geotechnical Engineer prior to transport to the site. Imported Structural Fill: Select granular materials imported for use as structural fill should meet the criteria for CDOT Class 1 Structure Backfill as tabulated below. Representative samples of proposed imported soils should be tested and approved by GROUND prior to transport to the site. CDOT Class 1 Structure Backfill Sieve Size or Parameter Acceptable Range 2-inch Sieve 100% passing No. 4 Sieve 30% to 100% passing No. 50 Sieve 10% to 60% passing No. 200 Sieve 5% to 20% passing Liquid Limit < 35 % Plasticity Index < 6 % Fill Platform Preparation: Prior to filling, the top 8 to 12 inches of in-place materials on which fill soils will be placed should be scarified, moisture conditioned and properly compacted in accordance with the recommendations below to provide a uniform base for fill placement. If over-excavation is to be performed, then these recommendations for subgrade preparation are for the subgrade below the bottom of the specified over- excavation depth. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 39 of 60 If surfaces to receive fill expose loose, wet, soft or otherwise deleterious material, additional material should be excavated, or other measures taken to establish a firm platform for filling. The surfaces to receive fill must be effectively stable prior to placement of fill. Fill Placement: Fill materials should be thoroughly mixed to achieve a uniform moisture content, placed in uniform lifts not exceeding 8 inches in loose thickness, and properly compacted. Soils that classify as GP, GW, GM, GC, SP, SW, SM, or SC in accordance with the USCS classification system (granular materials) should be compacted to 95 or more percent of the maximum modified Proctor dry density at moisture contents within 2 percent of optimum moisture content as determined by ASTM D1557. Soils that classify as ML, MH, CL or CH should be compacted to 100 percent of the maximum standard Proctor density beneath Building Structures and within the existing drainage area and compacted to 95 percent of the maximum standard Proctor density in all other areas at moisture contents from 1 percent below to 3 percent above the optimum moisture content as determined by ASTM D698. In addition, these fill soils must exhibit as-placed swells of 0.5 percent or less, against a 1,000 psf surcharge. Materials represented by samples exhibiting more than 0.5 percent swell upon wetting against a 1,000-psf surcharge should be re-worked at increased moisture contents and re-compacted in accordance with the recommendations herein. No fill materials should be placed, worked, rolled while they are frozen, thawing, or during poor/inclement weather conditions. Care should be taken with regard to achieving and maintaining proper moisture contents during placement and compaction. Materials that are not properly moisture conditioned may exhibit significant pumping, rutting, and deflection at moisture contents near optimum and above. The contractor should be prepared to handle soils of this type, including the use of chemical stabilization, if necessary. Compaction areas should be kept separate, and no lift should be covered by another until relative compaction and moisture content within the recommended ranges are obtained. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 40 of 60 Use of Squeegee: Relatively uniformly graded fine gravel or coarse sand, i.e., “squeegee,” or similar materials commonly are proposed for backfilling foundation excavations, utility trenches (excluding approved pipe bedding), and other areas where employing compaction equipment is difficult. In general, GROUND does not recommend this procedure for the following reasons: Although commonly considered “self compacting,” uniformly graded granular materials require densification after placement, typically by vibration. The equipment to densify these materials is not available on many job-sites. Even when properly densified, uniformly graded granular materials are permeable and allow water to reach and collect in the lower portions of the excavations backfilled with those materials. This leads to wetting of the underlying soils and resultant potential loss of bearing support as well as increased local heave or settlement. GROUND recommends that wherever possible, excavations be backfilled with approved, on-site soils placed as properly compacted fill. Where this is not feasible, use of “Controlled Low Strength Material” (CLSM), i.e., a lean, sand-cement slurry (“flowable fill”) or a similar material for backfilling should be considered. Where “squeegee” or similar materials are proposed for use by the contractor, the design team should be notified by means of a Request for Information (RFI), so that the proposed use can be considered on a case-by-case basis. Where “squeegee” meets the project requirements for pipe bedding material, however, it is acceptable for that use. Settlements: Settlements will occur in filled ground, typically on the order of 1 to 2 percent of the fill depth. If fill placement is performed properly and is tightly controlled, in GROUND’s experience the majority (on the order of 60 to 80 percent) of that settlement will typically take place during earthwork construction, provided the contractor achieves the compaction levels recommended herein. The remaining potential settlements likely will take several months or longer to be realized, and may be exacerbated if these fills are subjected to changes in moisture content. Cut and Filled Slopes: Permanent site slopes supported by on-site soils up to 10 feet in height may be constructed no steeper than 3:1 (horizontal : vertical). Minor raveling or surficial sloughing should be anticipated on slopes cut at this angle until vegetation is Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 41 of 60 well re-established. Surface drainage should be designed to direct water away from slope faces. EXCAVATION CONSIDERATIONS The test holes for the subsurface exploration were excavated to the depths indicated by means of truck-mounted, flight auger drilling equipment. We anticipate no significant excavation difficulties in the majority of the site with conventional heavy-duty excavation equipment in good working condition. We recommend that temporary, un-shored excavation slopes up to 10 feet in height be cut no steeper than 1:1 (horizontal : vertical) in the site soils in the absence of seepage. Sloughing on the slope faces should be anticipated at this angle. Local conditions encountered during construction, such as groundwater seepage and loose sand, will require flatter slopes. Stockpiling of materials should not be permitted closer to the tops of temporary slopes than 5 feet or a distance equal to the depth of the excavation, which ever is greater. Should site constraints prohibit the use of the recommended slope angles, temporary shoring should be used. The shoring should be designed to resist the lateral earth pressure exerted by building, traffic, equipment, and stockpiles. GROUND can provide shoring design upon request. Groundwater was encountered in the test holes at depths ranging from approximately 11 feet to 27 feet below existing grades at the time of drilling and at depths ranging from 12 to 19 feet across the site when measured 7 and 14 days later. Therefore, groundwater may be encountered in some sections of a trench or within the excavation of the structures. A properly designed and installed de-watering system may be required during the construction in these sections of the trench or below grade levels. The risk of slope instability will be significantly increased in areas of seepage along the excavation slopes. If seepage is encountered, the slopes should be re-evaluated by the Geotechnical Engineer. Additionally, drilled pier excavations will encounter groundwater, as well as hard/resistant bedrock. The Contractor should be prepared to penetrate resistant Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 42 of 60 bedrock and to install piers in the presence of groundwater. The sands penetrated during drilled pier installation may be vulnerable to caving. Good surface drainage should be provided around temporary excavation slopes to direct surface runoff away from the slope faces. A properly designed drainage swale should be provided at the top of the excavations. In no case should water be allowed to pond at the site. Slopes should also be protected against erosion. Erosion along the slopes will result in sloughing and could lead to a slope failure. Excavations in which personnel will be working must comply with all OSHA Standards and Regulations. Project excavations and shoring should be observed regularly by the Geotechnical Engineer throughout construction operations. The Contractor’s “responsible person” should evaluate the soil exposed in the excavations as part of the Contractor’s safety procedures. GROUND has provided the information above solely as a service to the Client, and is not assuming responsibility for construction site safety or the Contractor’s activities. UTILITY PIPE INSTALLATION AND BACKFILLING Pipe Support: The bearing capacity of the site soils appeared adequate, in general, for support of the proposed water line. The pipe + water are less dense than the soils which will be displaced for installation. Therefore, GROUND anticipates no significant pipe settlements in these materials where properly bedded. Excavation bottoms may expose soft, loose or otherwise deleterious materials, including debris. Firm materials may be disturbed by the excavation process. All such unsuitable materials should be excavated and replaced with properly compacted fill. Areas allowed to pond water will require excavation and replacement with properly compacted fill. The contractor should take particular care to ensure adequate support near pipe joints which are less tolerant of extensional strains. Where thrust blocks are needed, they may be designed for an allowable passive soil pressure of 250 psf per foot of embedment, to a maximum of 2,500 psf. Sliding friction at the bottom of thrust blocks may be taken as 0.33 times the vertical dead load. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 43 of 60 Trench Backfilling: Some settlement of compacted soil trench backfill materials should be anticipated, even where all the backfill is placed and compacted correctly. Typical settlements are on the order of 1 to 2 percent of fill thickness. However, the need to compact to the lowest portion of the backfill must be balanced against the need to protect the pipe from damage from the compaction process. Some thickness of backfill may need to be placed at compaction levels lower than recommended or specified (or smaller compaction equipment used together with thinner lifts) to avoid damaging the pipe. Protecting the pipe in this manner can result in somewhat greater surface settlements. Therefore, although other alternatives may be available, the following options are presented for consideration: Controlled Low Strength Material: Because of these limitations, we recommend backfilling the entire depth of the trench (both bedding and common backfill zones) with “controlled low strength material” (CLSM), i.e., a lean, sand-cement slurry, “flowable fill,” or similar material along all trench alignment reaches with low tolerances for surface settlements. We recommend that CLSM used as pipe bedding and trench backfill exhibit a 28-day unconfined compressive strength between 50 to 200 psi so that re-excavation is not unusually difficult. Placement of the CLSM in several lifts or other measures likely will be necessary to avoid ‘floating’ the pipe. Measures also should be taken to maintain pipe alignment during CLSM placement. Compacted Soil Backfilling: Where compacted soil backfilling is employed, using the site soils or similar materials as backfill, the risk of backfill settlements entailed in the selection of this higher risk alternative must be anticipated and accepted by the Client/Owner. We anticipate that the on-site soils excavated from trenches will be suitable, in general, for use as common trench backfill within the above-described limitations. Backfill soils should be free of vegetation, organic debris and other deleterious materials. Fragments of rock, cobbles, and inert construction debris (e.g., concrete or asphalt) coarser than 3 inches in maximum dimension should not be incorporated into trench backfills. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 44 of 60 If it is necessary to import material for use as backfill, the imported soils should be free of vegetation, organic debris, and other deleterious materials. Imported material should consist of relatively impervious soils that have less than 50 percent passing the No. 200 Sieve and should have a plasticity index of less than 15. Representative samples of the materials proposed for import should be tested and approved prior to transport to the site. Soils placed for compaction as trench backfill should be conditioned to a relatively uniform moisture content, placed and compacted in accordance with the recommendations in the Project Earthwork section of this report. Pipe Bedding: Pipe bedding materials, placement and compaction should meet the specifications of the pipe manufacturer and applicable municipal standards. Bedding should be brought up uniformly on both sides of the pipe to reduce differential loadings. As discussed above, we recommend the use of CLSM or similar material in lieu of granular bedding and compacted soil backfill where the tolerance for surface settlement is low. (Placement of CLSM as bedding to at least 12 inches above the pipe can protect the pipe and assist construction of a well-compacted conventional backfill, although possibly at an increased cost relative to the use of conventional bedding.) If a granular bedding material is specified, GROUND recommends that with regard to potential migration of fines into the pipe bedding, design and installation follow ASTM D2321. If the granular bedding does not meet filter criteria for the enclosing soils, then non-woven filter fabric (e.g., Mirafi® 140N, or the equivalent) should be placed around the bedding to reduce migration of fines into the bedding which can result in severe, local surface settlements. Where this protection is not provided, settlements can develop/continue several months or years after completion of the project. In addition, clay or concrete cut-off walls should be installed to interrupt the granular bedding section to reduce the rates and volumes of water transmitted along the sewer alignment which can contribute to migration of fines. If granular bedding is specified, the contractor should not anticipate that significant volumes of on-site soils will be suitable for that use. Materials proposed for use as pipe bedding should be tested by a geotechnical engineer for suitability prior to use. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 45 of 60 Imported materials should be tested and approved by a geotechnical engineer prior to transport to the site. SURFACE DRAINAGE The following drainage measures are recommended for design, construction, and should be maintained at all times after the project has been completed: 1) Wetting or drying of the foundation excavations and underslab areas should be avoided during and after construction as well as throughout the improvements’ design life. Permitting increases/variations in moisture to the adjacent or supporting soils may result in a decrease in bearing capacity and an increase in volume change of the underlying soils and/or differential movement. 2) Positive surface drainage measures should be provided and maintained to reduce water infiltration into foundation soils. The ground surface surrounding the exterior of each building should be sloped to drain away from the foundation in all directions. Ideally, we recommend a minimum slope of 12 inches in the first 10 feet in the areas not covered with pavement or concrete slabs, or a minimum 3 percent in the first 10 feet in the areas covered with pavement or concrete slabs. However, we realize that these recommended slopes cannot always be designed for this type of development. Therefore, lesser slopes can be used provided that positive surface drainage is implemented and routinely maintained throughout the life of the facility. In the event water is allowed to infiltrate the foundation soils, an increase in potential movements of the structures will occur. For areas of reduced slopes, subsurface drainage systems should be implemented in the design. 3) Reducing the slopes to comply with ADA requirements may be necessary but may result in an increased potential for moisture infiltration and subsequent volume change of the underling soils. In no case should water be allowed to pond near or adjacent to foundation elements. However, if positive surface drainage is implemented and maintained directing moisture away from the building, lesser slopes can be utilized. In no case should water be allowed to pond near or adjacent to foundation elements. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 46 of 60 4) On some sites it is common to have slopes descending toward buildings. Such slopes can be created during grading even on comparatively flat sites. In such cases, even where the recommendation above regarding slopes adjacent to the building is followed, water may flow to and beneath the building with resultant additional post-construction movements. Where the final site configuration includes graded or retained slopes descending toward the building or flatwork, interceptor drains should be installed between the building and the slope. In addition, where irrigation is applied on or above slopes, drainage structures commonly are needed near the toe-of-slope to prevent on-going or recurrent wet conditions. 5) In no case should water be permitted to pond adjacent to or on sidewalks, hardscaping, or other improvements as well as utility trench alignments, which are likely to be adversely affected by moisture-volume changes in the underlying soils or flow of infiltrating water. 6) Roof downspouts and drains should discharge well beyond the perimeters of the structure foundations (minimum 10 feet), or be provided with positive conveyance off-site for collected waters. 7) Based on our experience with similar facilities, the project site may consist of landscaping/watering near the building. Provided that positive, effective surface drainage is initially implemented and maintained throughout the life of the facility, vegetation that requires little to no watering may be located within 10 feet of the building perimeter. Irrigation sprinkler heads should be deployed so that applied water is not introduced near or into foundation/subgrade soils. The area surrounding the perimeter of the building should be constructed so that the surface drains away from the structure. Additionally, it is very important that landscape maintenance is performed such that the amount of moisture is strictly controlled so that the quantity of moisture applied is limited to that which is necessary to sustain the vegetation; in no case should saturated or marshy conditions be allowed to occur near any of the site improvements (including throughout the landscaped islands in parking areas). Periodic inspections should be made by facility representatives to make sure that the landscape irrigation is functioning properly and that excess moisture is not applied. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 47 of 60 8) Use of drip irrigation systems can be beneficial for reducing over-spray beyond planters. Drip irrigation can also be beneficial for reducing the amounts of water introduced to foundation/subgrade soils, but only if the total volumes of applied water are controlled with regard to limiting that introduction. Controlling rates of moisture increase in foundation/subgrade soils should take higher priority than minimizing landscape plant losses. 9) Where plantings are desired within 10 feet of a building, GROUND recommends that the plants be placed in water-tight planters, constructed either in-ground or above-grade, to reduce moisture infiltration in the surrounding subgrade soils. Planters should be provided with positive drainage and landscape underdrains. Colorado Geological Survey – Special Publication 43 provides additional guidelines for landscaping and reducing the amount of water that infiltrates into the ground. 10) Detention ponds commonly are incorporated into drainage design. When a detention ponds fills, the rate of release of the water is controlled and water is retained in the pond for a period of time. Where in-ground storm sewers direct surface water to the pond, the granular pipe bedding also can direct shallow groundwater or infiltrating surface water toward the pond. Thus, detention ponds can become locations of enhanced and concentrated infiltration into the subsurface, leading to wetting of foundation soils in the vicinity with consequent heave or settlement. Therefore, unless the pond is clearly down-gradient from the proposed buildings and other structures that would be adversely affected by wetting of the subgrade soils, including off-site improvements, GROUND recommends that the detention pond should be provided with an effective, low permeability liner. In addition, cut-off walls and/or drainage provisions should be provided for the bedding materials surrounding storm sewer lines flowing to the pond. 11) Plastic membranes should not be used to cover the ground surface adjacent to foundation walls. Perforated “weed barrier” membranes that allow ready evaporation from the underlying soils may be used. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 48 of 60 UNDERDRAIN/SUBSURFACE MOISTURE INFILTRATION Installation of an underdrain system is common practice for projects of this type. All below grade levels, partial below grade levels, crawl spaces, or other below grade void spaces should be provided with an underdrain system. Due to the proximity of the relocated drainage ditch, GROUND recommends that perimeter underdrains be installed for Blocks 4 through 6. An additional cut-off drain should also be installed between the building area and proposed water conveyance. If properly constructed, backfilled, and maintained, an effective underdrain system can collect free water that may otherwise infiltrate foundation/subgrade soils. Underdrains will not collect water infiltrating under unsaturated (vadose) conditions, or moving via capillarity. Furthermore, an underdrain not properly functioning can allow more moisture to infiltrate the foundation/subgrade soils and induce volume change of the soils, which may result in distress. Wetting or drying of the foundation excavations and underslab areas should be avoided during and after construction as well as throughout the life of the facility. Permitting increases/variations in moisture to the supporting soils may result in a decrease in bearing capacity and an increase in settlement, heave, and/or differential movement. Various elements of the project design, as well as site conditions before and after construction impact the need for incorporating an underdrain system into the project design. Design information regarding landscaping, flatwork, slopes, etc., was not available at the time this report was prepared, so it is therefore difficult to evaluate the need for an underdrain system. Upon request, our office is available to help evaluate the incorporation of an underdrain system or systems. Underdrain systems typically consist of rigid, perforated PVC drain pipe at least 4 inches in diameter, free-draining gravel, a water-proof membrane, and filter fabric constructed at a minimum slope of 1 percent. Upon completion and receipt of the final grading information and the selection of foundation type(s), GROUND can provide a detail of the perimeter drain as it relates to the proposed foundation system and minimum and maximum depth dimension from finish floor to the pipe invert. Additionally, GROUND can review the underdrain layout plans as they comply with this geotechnical study. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 49 of 60 PAVEMENT CONCLUSIONS/RECOMMENDATIONS Existing Pavement Section discussion Pavement thicknesses, based on our exploration program, ranged from 4 inches to 7 inches. Pavement distresses throughout the pavement area consisted of low to high severity longitudinal cracking and alligator/fatigue cracking. Some areas, appear to consist of recent localized preventive M & R (maintenance and rehabilitation) methods including full-depth patching, and thin asphalt overlays. At the time of this report preparation, it is unknown what areas will be reconstruction or rehabilitated. The area on the north side of the mall structure appear to be performing satisfactorily and rehabilitation/reconstruction may not be necessary while pavement areas on the east, west, and south sides of the existing mall exhibited moderate to high severity distress and rehabilitation/reconstruction may be deemed necessary. Below are photographs taken during our exploration program of the existing pavement sections. Additionally, areas that will include Ground Penetrating Radar analysis has not been defined by the Client, but will likely be performed in the future to better determine pavement thickesses. Phase 1 North side of the Foothills Mall – Pavement Performance Good Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 50 of 60 East side of Foothills Mall – Pavement Performance Fair to Poor West Side of Foothills Mall – Pavement Performance Fair Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 51 of 60 Phase 2 Phase 3 Phase 2 Area – Pavement Performance Fair Phase 3 Area – Pavement Performance Fair Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 52 of 60 Pavement Rehabilitation If an overlay is desired, areas consisting of longitudinal/transverse cracking should be sealed. In the event cracks greater than 2 inches in width are observed, removal and replacement of the asphalt in these severe cracking areas should take place prior to the overlay. A mill and overlay program consisting of at least 2 inches of asphalt may be feasible for pavements with at least 4.5 to 5 inches of existing asphalt if the resulting milled surface is stable enough to avoid “breaking through” the stable milled asphalt surface with heavy trucks and paving equipment. According to our core depths within the pavement areas, a mill and overlay program may be performed in most areas. If the owner chooses to conduct a minimum 2-inch mill and overlay program on site pavements, GROUND should be notified to evaluate the stability of a milled surface test section. Based on the condition of the milled surface, total removal may be required. Contractor bid schedules should contain costs for both scenarios. Although a mill and overlay program is a more cost effective means of improving a pavements structural capacity and correcting minor surface undulations, it should be noted that the risk of reflective cracking exists anytime a distressed pavement (a pavement containing various levels and types of cracking) is overlaid. GROUND recommends that GPR analysis be performed prior to performing a mill and overlay program. Pavement Reconstruction A pavement section is a layered system designed to distribute concentrated traffic loads to the subgrade. Performance of the pavement structure is directly related to the physical properties of the subgrade soils and traffic loadings. The standard care of practice in pavement design describes the recommended flexible pavement section as a “20-year” design pavement: however, most flexible pavements will not remain in satisfactory condition without routine maintenance and rehabilitation procedures performed throughout the life of the pavement. Pavement designs for the private pavements were developed in general accordance with the design guidelines and Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 53 of 60 procedures of the American Association of State Highway and Transportation Officials (AASHTO). Subgrade Materials Based on the results of our field exploration and laboratory testing, the potential pavement subgrade materials classify as A-1-a to A-6 soils in accordance with the American Association of State Highway and Transportation Officials (AASHTO) classification system. For the site soils, based on our experience, a resilient modulus of 4,195 psi was assumed for use in the pavement design. It is important to note that significant decreases in soil support have been observed as the moisture content increases above the optimum. Pavements that are not properly drained may experience a loss of the soil support and subsequent reduction in pavement life. Design Traffic GROUND attempted to retrieve traffic information, however, this information was unavailable. Based on our experience with similar facilities, an equivalent 18-kip daily load application (EDLA) value of 5 was assumed for the general parking lot areas. The EDLA value of 5 was converted to an equivalent 18-kip single axle load (ESAL) value of 36,500 for a 20-year design life. In areas of heavy truck traffic and drive lanes, an equivalent 18-kip daily load application (EDLA) value of 10 was assumed. The EDLA value of 10 was converted to an equivalent 18-kip single axle load (ESAL) value of 73,000 for a 20-year design life. If design traffic loadings differ significantly from these assumed values, GROUND should be notified to re-evaluate the pavement recommendations below. Pavement Design The soil resilient modulus and the assumed ESAL value were used to determine the required design structural number for the project pavements. The required structural number was then used to develop recommended pavement sections. Pavement designs were based on the DARWin™ computer program that solves the 1993 AASHTO pavement design equations. A Reliability Level of 80 percent and a terminal Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 54 of 60 serviceability of 2.0 were utilized for design of the pavement sections. A structural coefficient of 0.40 was used for hot bituminous asphalt and 0.12 was used for aggregate base course. The minimum pavement sections recommended by GROUND are tabulated below. Recommended Minimum Pavement Sections Location Full Depth Asphalt (inches Asphalt) Composite Section (inches Asphalt / inches Aggregate Base) Rigid Section (inches Concrete) Private Parking Lot 6 4.5 / 6 5 Private Drive Lanes and Heavy Truck Traffic 6.5 5 / 6 6 It has been GROUND’s experience that if properly constructed and maintained, a composite pavement section can provide better long-term performance. We recommend that primary delivery truck routes such as the dock area, trash collection area, as well as other pavement areas subjected to high turning stresses or heavy truck traffic be provided with rigid pavements consisting of 6 or more inches of Portland cement concrete. For enhanced performance, concrete sections should be underlain by 6 inches of properly compacted aggregate base. Reinforcement bar should be considered in rigid pavements to reduce differential movement when cracking occurs. Asphalt pavement should consist of a bituminous plant mix composed of a mixture of aggregate and bituminous material. Asphalt mixture(s) should meet the requirements of a job-mix formula established by a qualified Engineer. Concrete pavements should consist of a plant mix composed of a mixture of aggregate, Portland cement and appropriate admixtures meeting the requirements of a job-mix formula established by a qualified engineer. Concrete should have a minimum modulus of rupture of third point loading of 650 psi. Normally, concrete with a 28-day compressive strength of 4,000 psi should develop this modulus of rupture value. The concrete should Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 55 of 60 be air-entrained with approximately 6 percent air and should have a minimum cement content of 6 sacks per cubic yard. Maximum allowable slump should be 4 inches. In areas of repeated turning stresses we recommend that the concrete pavement joints be fully tied or doweled. We suggest that civil design consider joint layout in accordance with CDOT’s M Standards. Standard plans for placement of ties and dowels, etc., (CDOT M Standards) for concrete pavements can be found at the CDOT website: http://www.dot.state.co.us/DesignSupport/ If composite flexible sections are placed, the aggregate base material should meet the criteria of CDOT Class 6 aggregate base course. Base course should be placed in uniform lifts not exceeding 8 inches in loose thickness and compacted to at least 95 percent of the maximum dry density a uniform moisture contents within 3 percent of the optimum as determined by ASTM D1557 / AASHTO T-180, the “modified Proctor.” Subgrade Preparation Shortly before placement of pavement, including aggregate base, the exposed subgrade soils should be scarified and/or processed to a depth of at least 12 inches, mixed to achieve a uniform moisture content and then re-compacted in accordance with the recommendations provided in the Project Earthwork section of this report. Subgrade preparation should extend the full width of the pavement from back-of-curb to back-of- curb. As stated in the Exterior Flatwork section, greater depths of subgrade processing will further reduce potential pavement movements. The shallow processing depth indicated above will not eliminate potential movements. It is not possible to accurately correlate subgrade stability with information derived from site observations made during the geotechnical exploration or subsequent laboratory testing. It is often our experience that when pavements are removed, the pavement subgrade experiences instability when subjected to construction and/or traffic loading, even when laboratory testing suggests reasonable moisture contents and density. Therefore, it may be necessary to stabilize the majority of the existing subgrade prior to repaving. This may require reprocessing or chemical stabilization of existing soils or removal and replacement with other site materials or imported soil. Our office should be retained to observe the subgrade condition and stability during the removal process. If additional or more specific information is required, then we suggest removal Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 56 of 60 of several large sections of these pavement areas for evaluation prior to design or bidding. The Contractor should be prepared either to dry the subgrade materials or moisten them, as needed, prior to compaction. It may be difficult for the contractor to achieve and maintain compaction in some on-site soils encountered without careful control of water contents. Likewise, some site soils likely will “pump” or deflect during compaction if moisture levels are not carefully controlled. The Contractor should be prepared to process and compact such soils to establish a stable platform for paving, including use of chemical stabilization, if necessary. Immediately prior to paving, the subgrade should be proof rolled with a heavily loaded, pneumatic tired vehicle. Areas that show excessive deflection during proof rolling should be excavated and replaced and/or stabilized. Areas allowed to pond prior to paving will require significant re-working prior to proof-rolling. Passing a proof roll is an additional requirement, beyond placement and compaction of the subgrade soils in accordance with the recommendations in this report. Some soils that are compacted in accordance with the recommendations herein may not be stable under a proof roll, particularly at moisture contents in the upper portion of the acceptable range. Additional Observations The collection and diversion of surface drainage away from paved areas is extremely important to the satisfactory performance of the pavements. The subsurface and surface drainage systems should be carefully designed to ensure removal of the water from paved areas and subgrade soils. Allowing surface waters to pond on pavements will cause premature pavement deterioration. Where topography, site constraints, or other factors limit or preclude adequate surface drainage, pavements should be provided with edge drains to reduce loss of subgrade support. The long-term performance of the pavement also can be improved greatly by proper backfilling and compaction behind curbs, gutters, and sidewalks so that ponding is not permitted and water infiltration is reduced. Landscape irrigation in planters adjacent to pavements and in “island” planters within paved areas should be carefully controlled or differential heave and/or rutting of the nearby pavements will result. Drip irrigation systems are recommended for such Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 57 of 60 planters to reduce over-spray and water infiltration beyond the planters. Enclosing the soil in the planters with plastic liners and providing them with positive drainage also will reduce differential moisture increases in the surrounding subgrade soils. GROUND’s experience indicates that longitudinal cracking is common in asphalt- pavements generally parallel to the interface between the asphalt and concrete structures such as curbs, gutters or drain pans. Distress of this type is likely to occur even where the subgrade has been prepared properly and the asphalt has been compacted properly. As stated, some of these types of distress should be anticipated. The use of thick base course or reinforced concrete pavement can minimize this. Our office should be contacted if these alternates are desired. The design traffic loading does not include excess loading conditions imposed by heavy construction vehicles. Consequently, heavily loaded concrete, lumber, and building material trucks can have a detrimental effect on the pavement. GROUND recommends that an effective program of regular maintenance be developed and implemented to seal cracks, repair distressed areas, and perform thin overlays throughout the life of the pavements. CLOSURE Geotechnical Review The author of this report should be retained to review project plans and specifications to evaluate whether they comply with the intent of the recommendations in this report. The review should be requested in writing. The geotechnical recommendations presented in this report are contingent upon observation and testing of project earthworks by representatives of GROUND. If another geotechnical consultant is selected to provide materials testing, then that consultant must assume all responsibility for the geotechnical aspects of the project by concurring in writing with the recommendations in this report, or by providing alternative recommendations. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 58 of 60 Materials Testing The client should consider retaining a Geotechnical Engineer to perform materials testing during construction. The performance of such testing or lack thereof, in no way alleviates the burden of the contractor or subcontractor from constructing in a manner that conforms to applicable project documents and industry standards. The contractor or pertinent subcontractor is ultimately responsible for managing the quality of their work; furthermore, testing by the geotechnical engineer does not preclude the contractor from obtaining or providing whatever services they deem necessary to complete the project in accordance with applicable documents. Limitations This report has been prepared for the Walton Foothills Holdings VI, LLC as it pertains to the proposed Foothills Mall Redevleopment as described herein. It may not contain sufficient information for other parties or other purposes. The owner or any prospective buyer relying upon this report must be made aware of and must agree to the terms, conditions, and liability limitations outlined in the proposal. In addition, GROUND has assumed that project construction will commence by Spring 2013. Any changes in project plans or schedule should be brought to the attention of the Geotechnical Engineer, in order that the geotechnical recommendations may be re- evaluated and, as necessary, modified. The geotechnical conclusions and recommendations in this report relied upon subsurface exploration at a limited number of exploration points, as shown in Figure 1, as well as the means and methods described herein. Subsurface conditions were interpolated between and extrapolated beyond these locations. It is not possible to guarantee the subsurface conditions are as indicated in this report. Actual conditions exposed during construction may differ from those encountered during site exploration. If during construction, surface, soil, bedrock, or groundwater conditions appear to be at variance with those described herein, the Geotechnical Engineer should be advised at once, so that re-evaluation of the recommendations may be made in a timely manner. In addition, a contractor who relies upon this report for development of his scope of work or cost estimates may find the geotechnical information in this report to be inadequate for Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 59 of 60 his purposes or find the geotechnical conditions described herein to be at variance with his experience in the greater project area. The contractor is responsible for obtaining the additional geotechnical information that is necessary to develop his workscope and cost estimates with sufficient precision. This includes current depths to groundwater, etc. The materials present on-site are stable at their natural moisture content, but may change volume or lose bearing capacity or stability with changes in moisture content. ALL DEVELOPMENT CONTAINS INHERENT RISKS. It is important that ALL aspects of this report, as well as the estimated performance (and limitations with any such estimations) of proposed project improvements are understood by the Client, Project Owner (if different), or properly conveyed to any future owner(s). Utilizing these recommendations for planning, design, and/or construction constitutes understanding and acceptance of recommendations or information provided herein, potential risks, associated improvement performance, as well as the limitations inherent within such estimations. If any information referred to herein is not well understood, it is imperative for the Client, Owner (if different), or anyone using this report to contact the author or a company principal immediately. Performance of the proposed structures and pavement will depend on implementation of the recommendations in this report and on proper maintenance after construction is completed. Because water is a significant cause of volume change in soils and rock, allowing moisture infiltration may result in movements, some of which will exceed estimates provided herein and should therefore be expected by the owner. This report was prepared in accordance with generally accepted soil and foundation engineering practice in the project area at the date of preparation. GROUND makes no warranties, either expressed or implied, as to the professional data, opinions or recommendations contained herein. Because of numerous considerations that are beyond GROUND’s control, the economic or technical performance of the project cannot be guaranteed in any respect. Foothills Mall Redevelopment Fort Collins, Colorado Final Submittal Job No. 12-3649 Ground Engineering Consultants, Inc. Page 60 of 60 GROUND appreciates the opportunity to complete this portion of the project and welcomes the opportunity to provide the Owner with a cost proposal for construction observation and materials testing prior to construction commencement. Sincerely, GROUND Engineering Consultants, Inc. Amy Crandall, E.I. Reviewed by Andrew J. Suedkamp, P.E. Maximum dry density = 124.3 pcf 120.1 pcf Optimum moisture = 9.6 % 10.9 % Elev/ Classification Nat. Sp.G. LL PI % > % < Depth USCS AASHTO Moist. #4 No.200 ROCK CORRECTED TEST RESULTS UNCORRECTED MATERIAL DESCRIPTION Project No. Client: Remarks: Project: Date: Location: TH - 35-38, P4-P7, Top 5' Sample Number: 185 GROUND ENGINEERING CONSULTANTS, INC. ENGLEWOOD, CO. Figure ASTM D 698-07 Method A Standard s(CL) A-4(3) 29 10 13 58.0 12-3649 Walton Foothills Holdings, VI, LLC, c/o 09/24/ 8 Dry density, pcf 108 113 118 123 128 133 Water content, % - Rock Corrected - Uncorrected 57911131517 9.6%, 124.3 pcf 10.9%, 120.1 pcf Test specification: ASTM D 4718-87 Oversize Corr. Applied to Each Test Point COMPACTION TEST REPORT For Curve No. 185 Foothills Mall Redevelopment Maximum dry density = 122.1 pcf 118.9 pcf Optimum moisture = 9.8 % 10.7 % Elev/ Classification Nat. Sp.G. LL PI % > % < Depth USCS AASHTO Moist. #4 No.200 ROCK CORRECTED TEST RESULTS UNCORRECTED MATERIAL DESCRIPTION Project No. Client: Remarks: Project: Date: Sample Number: 177 GROUND ENGINEERING CONSULTANTS, INC. ENGLEWOOD, CO. Figure ASTM D 698-07 Method A Standard SC A-4(0) 26 9 9.8 38.7 12-3649 Walton Foothills Holdings, VI, LLC, c/o 09/21/ 9 Dry density, pcf 103 108 113 118 123 128 Water content, % - Rock Corrected - Uncorrected 46810121416 9.8%, 122.1 pcf 10.7%, 118.9 pcf Test specification: ASTM D 4718-87 Oversize Corr. Applied to Each Test Point COMPACTION TEST REPORT For Curve No. 177 Foothills Mall Redevelopment TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Sample Location Natural Natural Percent Atterberg Limits Percent Unconfined Water USCS AASHTO Test Moisture Dry Passing Liquid Plasticity Swell Compressive Soluble pH Resistivity Classifi- Classifi- Soil or Hole Depth Content Density Gravel Sand No. 200 Limit Index (Surcharge Strength Sulfates cation cation Bedrock Type No. (feet) (%) (pcf) (%) (%) Sieve (%) (%) Pressure PSF) (psf) (%) (ohm-cm) (GI) 1 4 6.6 113.8 21 62 17 23 9 -0.1 (500) - 0.01 9.0 14,594 SC A-2-4(0) Clayey Sand with Gravel 2 10 11.2 105.5 6 75 19 NV NP - - - - - SC A-2-4(0) Silty Sand 2 15 23.6 95.6 - - 40 25 9 - - - - - SC A-4(0) Very Clayey Sand 3 5 18.5 103.8 - - 54 32 10 0 (625) - - - - CL A-4(3) Sand and Clay 4 3 14.4 97.8 - - 32 30 7 -4.3 (375) - - - - SC-SM A-2-4(0) Clayey, Silty Sand 4 13 12.8 115.8 - - 25 NV NP - 4,384 - - - SM A-2-4(0) Silty Sandstone 5 4 1.7 S/D 65 31 4 24 6 - - - - - GW A-1-a(0) Gravel 8 9 5.4 S/D - - 24 19 5 - - 0.02 9.0 - SC-SM A-2-4(0) Clayey, Silty Sand 9 3 17.3 109.2 - - 49 35 11 - - - - - SC A-6(3) Sand and Clay 10 15 2.5 S/D 15 78 7 NV NP - - - - - SW-SM A-1-b(0) Sand with Gravel 11 22 14.3 109.1 - - 69 37 13 - 9,402 - - - CL A-6(8) Sandy Claystone 13 3 21.9 90.4 - - 88 36 12 - 3,020 - - - CL A-6(11) Sandy Clay 14 3 20.5 101.0 - - 83 40 16 - - 0.04 - - CL A-6(18) Sandy Clay 14 8 5.3 117.9 14 68 18 22 4 - - - - - SC A-1-b(0) Clayey Sand with Gravel 15 3 22.5 98.5 - - 89 44 15 - 6,382 - - - ML A-7-6(16) Sandy Clay/Silt 16 13 16.8 111.8 - - 70 39 16 0.6 (1,625) - - - - CL A-6(10) Sandy Claystone 17 4 10.6 109.1 - - 50 28 9 -1.5 (500) - - - - CL A-4(2) Sand and Clay 17 19 9.3 106.3 - - 43 37 10 - - - - - SC A-4(1) Very Clayey Sandstone 18 10 5.0 119.9 - - 19 24 5 - - - - - SC-SM A-2-4(0) Clayey, Silty Sand 18 20 17.7 111.3 0 54 46 29 8 - - - - - SC A-4(1) Sandstone/Claystone 19 8 8.9 113.7 - - 33 27 5 - - - - - SC-SM A-2-4(0) Clayey, Silty Sand 19 18 13.9 118.0 - - 35 27 5 -0.5 (2,250) - - - - SC-SM A-2-4(0) Clayey Silty Sandstone Job No. 12-3649 Gradation TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Sample Location Natural Natural Percent Atterberg Limits Percent Unconfined Water USCS AASHTO Test Moisture Dry Passing Liquid Plasticity Swell Compressive Soluble pH Resistivity Classifi- Classifi- Soil or Hole Depth Content Density Gravel Sand No. 200 Limit Index (Surcharge Strength Sulfates cation cation Bedrock Type No. (feet) (%) (pcf) (%) (%) Sieve (%) (%) Pressure PSF) (psf) (%) (ohm-cm) (GI) Gradation 20 4 17.9 97.9 - - 28 29 4 -1.2 (500) - - - - SM A-2-4(0) Silty Sand 21 4 6.1 117.1 - - 18 31 15 - - 0.01 8.5 8,127 SC A-2-6(0) Clayey Sand 21 9 10.0 99.3 10 50 40 31 10 - - - - - SC A-4(1) Very Clayey Sand 22 3 20.8 103.8 - - 87 47 17 - - - - - CL A-7-6(18) Sandy Clay 22 13 3.6 S/D 16 77 7 NV NP - - - - - SW-SM A-1-b(0) Sand with silt and gravel 23 3 15.6 104.9 - - 27 34 9 0 (375) - - - - SM A-2-4(0) Silty Sand 23 23 17.8 107.7 - - 81 44 20 - 6,479 - - - CL A-7-6(17) Sandy Claystone 24 4 12.0 114.1 - - 46 30 9 - - 0.03 8.6 6,670 SM A-4(1) Sand and Clay/Silt 24 9 1.9 S/D 24 72 4 NP NV - - - - - SM A-1-b(0) Silty Sand 25 5 19.2 98.3 - - 26 41 7 -1.6 (625) - - - - SM A-2-5(0) Silty Sand 26 18 15.3 119.0 - - 43 29 10 - - - - - SM A-4(1) Very Silty Sand 27 9 5.8 112.7 - - 15 NV NP - - - - - SM A-2-4(0) Sility Sand 27 24 18.9 104.4 - - 71 46 20 - 5,261 - - - CL A-7-6(14) Sandy Claystone 28 4 11.1 110.6 - - 61 33 13 - - - - - CL A-6(6) Sandy Clay 28 29 17.5 104.7 - - 91 50 23 - 2,923 - - - CH A-7-6(24) Slightly Sandy Claystone 29 3 16.5 104.5 - - 41 40 10 - - - - - CL A-4(1) Very Silty Sand 31 4 23.0 103.0 - - 69 40 18 -0.2 (500) - - - - CL A-6(11) Sandy Clay 31 14 17.5 111.8 - - 32 34 4 - - - - - SM A-2-4(0) Silty Sandstone 32 8 19.8 105.3 - - 65 35 18 -0.5 (1,000) - - - - CL A-6(9) Sandy Clay 33 5 20.1 103.7 - - 76 38 18 - - <0.01 8.5 2,264 CL A-6(13) Sandy Clay 34 4 9.1 116.2 4 58 38 30 10 - - - - - SC A-4(0) Clayey Sand Job No. 12-3649 TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Sample Location Natural Natural Percent Atterberg Limits Percent Unconfined Water USCS AASHTO Test Moisture Dry Passing Liquid Plasticity Swell Compressive Soluble pH Resistivity Classifi- Classifi- Soil or Hole Depth Content Density Gravel Sand No. 200 Limit Index (Surcharge Strength Sulfates cation cation Bedrock Type No. (feet) (%) (pcf) (%) (%) Sieve (%) (%) Pressure PSF) (psf) (%) (ohm-cm) (GI) Gradation 34 9 2.7 S/D 35 56 9 NV NP - - - - - SP-SM A-1-a(0) Slightly Silty Sand 35 5 17.0 107.0 - - 49 31 10 -0.4 (625) - - - - SC A-4(2) Sand and Clay 35 15 22.0 S/D - - 36 24 7 - - - - - SC-SM A-2-4(0) Clayey, Silty Sand 37 9 10.8 114.3 - - 43 26 10 - - - - - SC A-4(1) Very Clayey Sand 37 14 17.6 107.6 - - 44 29 10 - - - - - SC A-4(1) Very Clayey Sand 37 24 15.6 110.1 - - 63 41 9 - 4,531 - - - ML A-5(5) Sandy Siltstone 38 3 17.1 103.6 - - 84 37 14 - - - - - CL A-6(12) Sandy Clay 38 8 8.7 112.9 - - 36 28 7 - - - - - SC A-4(0) Clayey, Silty Sand P1 4 19.8 105.4 - - 55 27 9 - - - - - CL A-4(2) Sand and Clay P2 3 19.6 104.6 - - 65 39 17 - - 0.03 8.4 - CL A-6(9) Sandy Clay P3 5 20.6 103.4 - - 69 35 15 0.3 (200) - - - - CL A-6(9) Sandy Clay P4 2 19.4 97.6 - - 34 33 8 - - - - - SC A-2-4(0) Clayey Sand P5 3 7.2 110.1 16 61 23 14 0 - - 0.01 8.7 8,277 SM A-1-a(0) Silty Sand P6 4 4.2 S/D - - 12 20 7 - - - - - SC-SM A-2-4(0) Clayey, Silty Sand P7 5 17.6 108.1 - - 41 31 12 0.1 (200) - - - - SC A-6(1) Very Clayey Sand P8 4 21.7 102.4 - - 82 40 20 - - <0.01 8.2 2,252 CL A-6(16) Sandy Clay P9 3 18.7 105.8 - - 63 38 17 0.6 (200) - - - - CL A-6(9) Sandy Clay P10 5 7.8 109.8 - - 28 20 4 - - 0.02 8.9 11,123 SM A-2-4(0) Silty Sand P11 4 19.9 101.4 - - 86 40 17 0 (200) - - - - CL A-6(15) Sandy Clay I1 9 3.1 S/D 11 82 7 NV NP - - - - - SP-SM A-1-b(0) Slightly Silty Sand I2 3 13.2 96.7 0 10 90 38 15 - - - - - CL A-6(14) Slightly Sandy Clay 35-38 1-5 9.3* 124.3* 13 29 58 29 10 - - - - - CL A-4(3) Sandy Clay 1-5 1-5 9.8* 122.1* 10 51 39 26 9 - - - - - SC A-4(0) Clayey Sand * Indicates optimum moisture content and maximum standard Proctor density (ASTM D-698) Job No. 12-3649 TABLE 2 SUMMARY OF LABORATORY TEST RESULTS Sample Location Water Redox Sulfides USCS Test Soluble pH Potential Content Resistivity Classifi- Soil or Hole Depth Sulfates cation Bedrock Type No. (feet) (%) (mV) (ohm-cm) 1 4 0.01 9.0 -115 Trace 14,594 SC Clayey Sand with Gravel 8 9 0.02 9.0 -118 Trace - SC-SM Clayey, Silty Sand 14 3 0.04 8.9 -97 Positive - CL Sandy Clay 21 4 0.01 8.5 -88 Trace 8,127 SC Clayey Sand 24 4 0.03 8.6 -93 Positive 6,670 SM Sand and Clay/Silt 33 5 <0.01 8.5 -159 Positive 2,264 CL Sandy Clay P2 3 0.03 8.4 -82 Trace - CL Sandy Clay P8 4 <0.01 8.2 -70 Positive 2,252 CL Sandy Clay P10 5 0.02 8.9 -109 Positive 11,123 SM Silty Sand Job 12-3649 TABLE 3 PERCOLATION TEST RESULTS Test Date: 9/25/2012 Tested By: JC Hole Hole Time Initial Ending Drop in Percolation No. Depth Interval Water Water Water Rate Depth Depth Level (inches) (minutes) (inches) (inches) (inches) (min/in) 30 32 30 2 15 1 36.0 30 30 28 2 15 30 28 26 2 15 30 26 24.75 1.25 24 30 24.75 23 1.75 17 30 23 22.25 0.75 40 30 22.25 21.75 0.5 60 30 21.75 21.25 0.5 60 30 31.5 29.75 1.75 17 2 36.0 30 29.75 29.25 0.5 60 30 29.25 28.75 0.5 60 30 28.75 28.15 0.6 50 30 28.15 27.75 0.4 75 30 27.75 27.25 0.5 60 30 27.25 26.75 0.5 60 30 26.75 26.25 0.5 60 30 32.00 29 3 10 3 36.0 30 29 28.1 0.9 33 30 28.1 27.3 0.8 38 30 27.3 26.75 0.55 55 30 26.75 26.3 0.45 67 30 26.3 25.8 0.5 60 30 25.8 25.4 0.4 75 30 25.4 25 0.4 75 30 25 24.5 0.5 60 Average Percolation Rate (min/in) = 61 TABLE 4 PERCOLATION TEST RESULTS Test Date: 9/25/2012 Tested By: JC Hole Hole Time Initial Ending Drop in Percolation No. Depth Interval Water Water Water Rate Depth Depth Level (inches) (minutes) (inches) (inches) (inches) (min/in) 33 32.75 30 2.75 12 1 36.0 32.75 32.5 28 4.5 7 30 32.5 32.25 0.25 120 30 32.25 32.125 0.125 240 30 32.125 31.875 0.25 120 30 31.875 31.75 0.125 240 30 31.75 31.5 0.25 120 30 31.5 31.25 0.25 120 30 33.5 33.25 0.25 120 2 36.0 30 33.25 33 0.25 120 30 33 32.875 0.125 240 30 32.875 32.75 0.125 240 30 32.75 32.5 0.25 120 30 32.5 32.375 0.125 240 30 32.375 32.25 0.125 240 30 32.25 32.125 0.125 240 30 33.50 33.25 0.25 120 3 36.0 30 33.25 33 0.25 120 30 33 32.875 0.125 240 30 32.875 32.625 0.25 120 30 32.625 32.5 0.125 240 30 32.5 32.375 0.125 240 30 32.5 32.375 0.125 240 30 32.375 32.25 0.125 240 30 32.25 32.125 0.125 240 Average Percolation Rate (min/in) = 213 APPENDIX A Geophysical Investigation Report 12217 Ground Engineering Consultants, Foothills Mall, Fort Collins 1 December 3, 2012 Amy Crandall, E.I. Ground Engineering Consultants, Inc. 41 Inverness Drive East Englewood, CO 80112 Subject: Geophysical Investigation Report – Foothills Mall, Fort Collins, Colorado This letter report presents results from the geophysical investigation conducted at the Foothills Mall, Fort Collins, Colorado (see Figure 1). Zonge International, Inc. (Zonge) performed the geophysical investigation under subcontract to Ground Engineering Consultants, Inc (Ground). Field data were acquired on November 27, 2012, by Chad Quinn and Matt Botruff. The objective of the geophysical investigation at the project site was to determine the one- dimensional shear-wave velocity (Vs) structure to a depth of at least 100 feet and to calculate the weighted velocity average of the top 100 feet (Vs100). One-dimensional (1D) seismic refraction microtremor (ReMi) soundings were used to measure Vs100 values along four lines to achieve the project objectives. This report summarizes site conditions, field methods, data acquisition, and results/interpretations for the investigation. Site Conditions The area of investigation is located at the south/south-east end of the Foothills Mall in Fort Collins, Colorado. Figure 1 shows the general site location, and Figure 2 shows the layout of the ReMi survey lines. The site encompassed an empty lot (no vegetation and rounded cobbles) that is bounded by Stanford Road to the east, E. Monroe Drive to the south, and the Foothills Mall to the west. These streets have heavy traffic and provided an excellent ambient energy source for ReMi data acquisition. 7711 West 6th Ave, Suite #G Lakewood, CO 80214 Phone: (720) 962-4444 Fax: 720-962-0417 zongecolo@zonge.com 12217 Ground Engineering Consultants, Foothills Mall, Fort Collins 2 Data Acquisition ReMi data were acquired on November 27, 2012, using a Geode 24-channel digital seismograph. This system utilizes a state of the art, 24-bit seismograph connected to a field laptop via ethernet cable. Analog data from the geophones are collected in the Geode seismograph where the data are digitized, transmitted to the laptop computer, and then recorded on the hard drive. For all four lines, 24 receivers (4.5-Hz vertical component geophones) were placed on the ground with 10 foot spacing’s (for a total array length of 230 feet) and coupled to the ground using a combination of either base plates or spikes. For the ReMi method, there are no predefined source points. Instead, the method uses ambient noise, or vibrational energy, that exists at a site. For this project, ambient noise was largely the result of traffic activity from the surrounding streets. These small-strain vibrations cause surface wave energy to propagate across the site, which is the seismic energy measured and recorded by the ReMi method. More than ten, unfiltered, 30-second ambient vibrational energy records (i.e., ‘noise’ records) were recorded for each line using a 2 msec sample rate. Data Processing The ReMi method calculates the shear-wave velocity (Vs) of layers and the respective depths to interfaces beneath the seismic line as described by Louie (2001). The ReMi method is primarily used to calculate shear velocity versus depth at a point (1D) to satisfy building code requirements (International Building Code – IBC) with regard to earthquake design and wind loading. In addition to providing a 1D sounding, the analysis also computes the average shear-wave velocity at a depth of 100 feet (30 m) as detailed in Table 1613.5.2 of the 2006 International Building Code (IBC); that is the “Vs100.” The data collected at this site were processed using the SeisOpt® ReMi™ software (© Optim LLC, 2005). There are three main processing steps to derive the Vs profiles: Step 1: Create a velocity spectrum (slowness-frequency (p-f) image) from the noise data. The distinctive slope of dispersive waves is the advantage of the p-f analysis. Other arrivals that appear in microtremor records, such as body waves and airwaves cannot have such a slope. Even if most of the energy in a seismic record is a phase other than Rayleigh waves, the p-f analysis will separate that energy in the slowness-frequency plot away from the dispersion curves this technique interprets. Step 2: Rayleigh-wave dispersion picking - Picking is done along a lowest p-f envelope bounding the energy that appears in the p-f image. Choosing the lowest energy envelope minimizes the effects of obliquely located surface wave sources that result in fast apparent velocities which create misleading Vs models. Step 3: Shear wave velocity modeling - The ReMi method interactively forward-models the normal-mode dispersion data picked from the p-f images with a code adapted from Saito (1979, 1988). This code produces results comparable to those of the forward-modeling codes used by Iwata et al. (1998), and by Xia et al. (1999) within their inversion procedure. The modeling iterates on phase velocity at each period (or frequency) and reports when a solution has been 12217 Ground Engineering Consultants, Foothills Mall, Fort Collins 3 found within the iteration parameters. This analysis approach and the propagation properties of surface waves allows velocity reversals (low shear-wave velocity layers at depth) to be modeled successfully. Results / Interpretations ReMi Vs100 shear-wave velocity results are presented in Figures 3 through 6. The Vs100 profiles represent a one-dimensional (1D) seismic sounding centered at the middle of each ReMi array. Thus, about halfway along each line would be the representative location of the 1D Vs data, if we were comparing results from a downhole or crosshole seismic test, for example. Locations for the ReMi lines were chosen based on the access and oriented with respect to possible noise sources. The overall environment allowed for acceptable data acquisition, and the quality of the data was good (repeatable). Therefore it was not necessary for any data files to be removed for further processing. As described in the previous section, ReMi data are derived by averaging the ambient noise across the geophone array and as such represent the bulk properties of the soil and/or rock beneath the array. Vs100 results from ReMi surveys have been shown in to be within 10-15% of Vs data obtained via crosshole or downhole testing, and can typically determine the depth to competent layers or bedrock also to within 10 to 15 percent. ReMi data obtained at this site indicate: Line 1 Vs100 = 1712 ft/s (feet/second), Line 2 Vs100 = 1922 ft/s, Line 3 Vs100 = 1380 ft/s, and Line 4 Vs100 = 1253 ft/s The average Vs100 value for all ReMi lines at this site is Vs100 = 1,567 ft/s. The Vs100 values listed here, and presented in Figures 3-6 and in Table 1, were computed in order to be used with Table 1613.5.2 of IBC 2006, or current equivalent. Velocity values and layer depths derived by the ReMi inversion process are also presented in Figures 3-6, and in Table 1. Based on the ReMi seismic results, unaltered bedrock is interpreted to be approximately 31 to 39 feet beneath the lines. The interpreted depth to bedrock is based on Vs values greater than or equal to 1,300 ft/s. All models show some increase in Vs around this depth, and the general trend in the models correlate with each other. There is a relatively wide velocity range between the four lines. Lines 3 and 4 show a lower velocity value in the interpreted bedrock than Lines 1 and 2. This could indicate that something is different in the geology between the east and west ends of the site. Bore-logs provided by Ground (referring to test hole 27 and 28) displayed density changes at shallower depths, but these depths and densities appear to vary site wide. Another possibility is that the low frequency content of the seismic signal was different between the first two and last two lines, resulting in better velocity constraint for one set of lines than the other. Based on the field conditions (sources and their locations relative to the geophone arrays), the data, and the resultant models, the data show that the overall Vs100 value for this project site is measured to be near 1567 ft/s. The four individual Vs100 values and their average equate to an 12217 Ground Engineering Consultants, Foothills Mall, Fort Collins 4 IBC site classification which can be referenced off of the appropriate IBC site classification table. We do not assign a site classification based on Vs measurements, because we are aware that other site factors may influence the classification. Site classification is an engineering judgment and decision; Zonge is presenting Vs profiles and the resultant average shear-wave velocities in graphical and tabular format (computed according to IBC specifications) beneath each ReMi array. Due caution and a conservative approach should be employed when evaluating site conditions and structural and foundation designs at any project site including sites in Fort Collins, Colorado, where the seismic hazard is sometimes underestimated. If you have any questions regarding the field procedures, seismic analysis techniques, or the results and interpretations presented herein, please do not hesitate to contact us. We appreciate working with you and look forward to providing Ground Engineering Consultants, Inc. with geophysical services in the future. Respectfully, Chad Quinn Zonge International, Inc. 12217 Ground Engineering Consultants, Foothills Mall, Fort Collins 5 References Iwata, T., Kawase, H., Satoh, T., Kakehi, Y., Irikura, K., Louie, J. N., Abbott, R. E., and Anderson, J. G., 1998, Array microtremor measurements at Reno, Nevada, USA (abstract): Eos, Trans. Amer. Geophys. Union, v. 79, suppl. to no. 45, p. F578. Louie, J, N., 2001, Faster, Better: Shear-wave velocity to 100 meters depth from refraction microtremor arrays: Bulletin of the Seismological Society of America, v. 91, p. 347-364. Pullammanappallil, S.K., and Louie, J.N., 1993, Inversion of seismic reflection travel times using a nonlinear optimization scheme: Geophysics, v. 58, p. 1607-1620. Pullammanappallil, S.K., and Louie, J.N., 1994, A generalized simulated-annealing optimization for inversion of first arrival times: BSSA, v. 84, p. 1397-1409. Saito, M., 1979, Computations of reflectivity and surface wave dispersion curves for layered media; I, Sound wave and SH wave: Butsuri-Tanko, v. 32, no. 5, p. 15-26. Saito, M., 1988, Compound matrix method for the calculation of spheroidal oscillation of the Earth: Seismol. Res. Lett., v. 59, p. 29. Xia, J., Miller, R. D., and Park, C. B., 1999, Estimation of near-surface shear-wave velocity by inversion of Rayleigh wave: Geophysics, v. 64, p.691-700. 12217 Ground Engineering Consultants, Foothills Mall, Fort Collins 6 Table 1- ReMi Inversion Results Line 1 Line 2 Line 3 Line 4 Depth (ft) Vs (ft/s) Depth (ft) Vs (ft/s) Depth (ft) Vs (ft/s) Depth (ft) Vs (ft/s) 0-13 698 0-5 587 0-8 664 0-5 446 13-25 909 5-16 820 8-28 742 5-7 674 25-34 931 16-30 1031 28-35 798 7-40 807 34-40 2043 30-38 2766 35-39 1087 40-67 1943 40-100 4244 38-100 4411 39-58 2110 67-100 3044 58-100 3500 Vs100= 1712 Vs100= 1922 Vs100= 1380 Vs100= 1253 12217 Ground Engineering Consultants, Foothills Mall, Fort Collins 7 12217 Ground Engineering Consultants, Foothills Mall, Fort Collins 8 12217 Ground Engineering Consultants, Foothills Mall, Fort Collins 9 Figure 3. Geophysical survey line 1 velocity sounding Figure 4. Geophysical survey line 2 velocity sounding 12217 Ground Engineering Consultants, Foothills Mall, Fort Collins 10 Figure 5. Geophysical survey line 3 velocity sounding Figure 6. Geophysical survey line 4 velocity sounding Grade Uniform Fill Prism or 12- inch Scarification beneath Footings and Slabs Phase 3 – Blocks 4 to 6 Spread Footings/Slab-on- Grade Uniform Fill Prism