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HomeMy WebLinkAboutHELLENIC PLAZA - Filed GR-GEOTECHNICAL REPORT/SOILS REPORT -GEOTECHNICAL ENGINEERING REPORT PROPOSED HELLENIC PLAZA P.U.D. RTHWEST CORNER OF SOUTH SHEILDS STREET AND BIRCH STREE1 FORMER CSU FRATERNITY HOUSE FORT COLLINS, LARIMER COUNTY, COLORADO TERRACON PROJECT NO.20075011 FEBRUARY 26, 2007 erracon Consulting Engineers & Scientists GEOTECHNICAL ENGINEERING REPORT I j PROPOSED HELLENIC PLAZA P.U.D. NORTHWEST CORNER OF SOUTH SHEILDS STREET AND BIRCH STREET FORMER CSU FRATERNITY HOUSE FORT COLLINS, LARIMER COUNTY, COLORADO TERRACON PROJECT NO. 20075011 FEBRUARY 26, 2007 Prepared for: Hellenic Plaza, LLC P.O. Box 1613 Fort Collins, Colorado 80522 Attn: Barbara Siek 1 7-7 Prepared by: Terracon 301 North Howes Street Fort Collins, Colorado 80521 rt 1'L lIerracon 1 1 ? i February 26, 2007 1 lerracon Consulting Engineers&Scientists Hellenic Plaza, LLC l' i P.O. BOX 1613 301 North HowesFortCollins,Colorado 80521 Fort Collins, Colorado_80522 Phone 970.484.0359LFax970.484.0454 Attn: Barbara Siek www.terracon.com Re: Geotechnical Engineering Report Proposed Hellenic Plaza P.U.D. i... I ' Northwest Corner of South Shields Street and Birch Street Former CSU Fraternity House Fort Collins, Larimer County, Colorado Terracon Project No. 20075011 Terracon has completed a geotechnical engineering exploration for the proposed Hellenic Plaza project planned for the vacant lot situated at the northwest corner of Shields Street and Birch Street in Fort Collins, Colorado. This study was performed in general accordance with our Proposal No. D2006393 dated October 16,2006. The results of our recent engineering study completed for the proposed development, including the 4 boring location diagram, test boring records, and the geotechnical recommendations needed to aid in the design of foundations, floor slabs, pavement, and other earth connected phases of this project are attached. Based on the geotechnical engineering analyses, subsurface exploration and laboratory test results, I. Terracon recommends the proposed building be supported by conventional-type spread footings bearing upon approved engineered fill material Slab-on-grade construction is feasible provided the recommendations set forth in this report are followed. iWe appreciate being of service to you in the geotechnical engineering phase of this project, and are prepared to assist you during the construction phases as well. If you have any questions concerning this report or any of our testing, inspection, design and consulting services please feel free to contact j us. Sincerely, Vo a`Q.....Ric..<p i TERRACO ;'T IO wl9• 6f e Y 0 2 b(2&- David A. Ric fP° ......•° ~ Mike Walker, CET q,, Geotechnical D ager Construction Services Manager rf Copies to: Addressee(3) Architecture West,LLC(4): Mr.Jeff Benham 3,..i Delivering Success for Clients and Employees Since 1965 More Than 80 Offices Nationwide i TABLE OF CONTENTS Page No. Letter of Transmittal I INTRODUCTION 1 PROPOSED CONSTRUCTION 1 SITE EXPLORATION 2 Field Exploration 2 Laboratory Testing 2 46 SITE CONDITIONS 3 1 SUBSURFACE CONDITIONS 3 Subsurface Soil Conditions 3 7.] Field and Laboratory Test Results 4 Swell -Consolidation Test Results 4 Groundwater Conditions 5 ENGINEERING RECOMMENDATIONS 6 Geotechnical Considerations 6 Foundation Systems—Conventional Type Spread Footings 6 Basement Construction 8 Lateral Earth Pressures 8 Seismic Considerations 9 Floor Slab Design and Construction 10 Pavement Design and Construction (For Non-Jurisdictional On-Site Areas) 11 Earthwork 15 General Considerations 15 Site Preparation 15 Subgrade Preparation 96 Fill Materials and Placement 16 Excavation and Trench Construction 17 Additional Design and Construction Considerations 18 Exterior Slab Design and Construction 18 1 i Corrosion Protection 18 Underground Utility Systems 19 1---,; Surface Drainage 19 GENERAL COMMENTS 19 APPENDIX A Boring Location Diagram—Figure No. 1 Logs of Borings—Nos. 1 through 8 APPENDIX B Laboratory Test Results APPENDIX C General Notes 1 ir.. iii I - GEOTECHNICAL ENGINEERING REPORT L PROPOSED HELLENIC PLAZA P.U.D. NORTHWEST CORNER OF SOUTH SHEILDS STREET AND BIRCH STREET FORMER CSU FRATERNITY HOUSELFORTCOLLINS, LARIMER COUNTY, COLORADO j TERRACON PROJECT NO. 20075011 FEBRUARY 26, 2007 LINTRODUCTION This report contains the results of ourgeotechnical engineering exploration for the proposedpg9PPp Hellenic Plaza project planned for the vacant lot situated at the northwest corner of Shields Street and Birch Street in Fort Collins, Colorado. The site is located in the Northeast A of Section 15, LTownship 7 North, Range 69 West of the 6th Principal Meridian, Larimer County, Colorado. The purpose of these services is to provide information and geotechnical engineering recommendations relative to: subsurface soil conditions L groundwater conditions foundation design and construction 1- 4 floor slab design and construction lateral earth pressures pavement design and construction earthwork Li drainage II The recommendations contained in this report are based upon the results of field and laboratory I _ testing, engineering analyses, and experience with similar soil conditions, structures and our understanding of the proposed project. PROPOSED CONSTRUCTION The project as we understand it is to construct the Hellenic Plaza, a proposed mixed use retail/residential establishment including on-site paved areas and a 30-foot wide fire lane, at the northwest corner of South Shields Street and Birch Street. A CSU Fraternity House, at one time, occupied the site. The architect has provided Terracon with a schematic/conceptual site plan for future/proposed building and drive entrance/parking areas. We assume the proposed single to 2- story building will have either slab on grade or full-depth basement construction, and will consist of wood framed or CMU wall units with brick veneer. The maximum wall and column loads are t r` I Geotechnical Engineering Report Terra= Hellenic Plaza,Inc. NIW/C of Shields Street and Birch Street Fort Collins,Larimer County,Colorado Project.No.20075011 assumed to be on the order of 1 to 4 klf and 10 to 75 kips respectively. We assume finished floor elevation will be within 2 feet of existing site grades. SITE EXPLORATION LThe scope of the services performed for this project included a site reconnaissance by an engineering geologist, a subsurface exploration program, laboratory testing and engineering analyses. Field Exploration LA total of eight test borings were drilled for the project on February 8 and 13, 2007 at the locations as shown on the Test Boring Location Diagram, Figure 1 included in Appendix A. The test borings were located within the footprint and planned parking areas and were extended to approximate depths of 10 to 20-feet below site grades. The borings were advanced with atruck- Jmounted drilling rig, utilizing 4-inch diameter solid stem augers. The borings were located in the field by pacing from existing site features and by using a hand held GPS unit. Ground surface elevations were estimated at each boring location by use of an engineer's level and referenced to a temporary benchmark (TBM) as shown on the enclosed Site Plan, Figure No. 1. The accuracy of boring locations and elevations should only be assumed to the level implied by the methods used. Lithologic logs of each boring were recorded by the engineering geologist during the drilling operations. At selected intervals, samples of the subsurface materials were taken by means of driving split-spoon and ring barrel samplers. Penetration resistance measurements were obtained by driving the split-spoon and ring barrel into the subsurface materials with a 140-pound hammer falling 30 inches. The penetration resistance value is a useful index in estimating the consistency, relative density or hardness of the materials encountered. µ . Laboratory Testing All samples retrieved during the field exploration were returned to the laboratory for observation by x the project geotechnical engineer and were classified in general accordance with the Unified Soil Classification System described in Appendix C. At that time, the field descriptions were confirmed or modified as necessary and an applicable laboratory testing program was formulated to 2 Geotechnical Engineering Report Terracon Hellenic Plaza,Inc. NIW/C of Shields Street and Birch Street Fort Collins, Larimer County,Colorado Project No.20075011 L.. determine engineering properties of the subsurface materials. Boring logs were prepared and are Ipresented in Appendix A. Laboratory tests were conducted on selected soil samples and are presented in Appendix B. The test results were used for the geotechnical engineering analyses, and the development of L foundation and earthwork recommendations. All laboratory tests were performed in general accordance with the applicable local or other accepted standards. Selected soil samples were Ltested for the following engineering properties: Water Content o Swell-Consolidation L Dry Density Atterberg Limits and % (-) No. 200 Sieve Water Soluble Sulfates SITE CONDITIONS The site for the proposed development is presently a vacant lot situated at the northwest corner of South Shields Street and Birch Street, adjacent to the Colorado State University's main campus, in Fort Collins, Colorado. An existing abandoned single family residential structure occupies the northeast portion of the site. We understand this building will be razed to accommodate the planned development. At one time a CSU Fraternity House occupied the southern portion of the site. This building was razed in early 2006 and the footprint was backfilled with imported soils. Terracon personnel were on-site on a "part-time/as-needed" basis during the backfill operations to conduct periodic or random field density tests when requested or called upon by the contractor. The majority of the site is sparsely vegetated with weed growth, is relatively flat, and exhibits fair surface drainage in the south to southeast directions. Two mature cottonwood trees are located north of and in the general vicinity of Test Boring Nos. 6 and 7. North is an existing residence, east is Shields Street, south is Birch Street and west is an existing sorority house. SUBSURFACE CONDITIONS The subsurface soils encountered across the site within our eight test borings, generally consisted of approximately 2 to 9-1/2-feet of sandy lean clay with trace amounts of gravel fill material, which extended to the native cohesive subsoils below. Underlying the fill material and extending to the depths explored and/or to the fine granular soils below, was the native sandy lean clay. In Boring Nos. 1, 2 and 4, a fine silty sand or sandy silt lenses was encountered at an approximate depth of 12-feet, and extended to the depths explored. 3 ram'' L-, I: 1 Geotechnical Engineering Report Terracon L Hellenic Plaza,Inc. NNV/C of Shields Street and Birch Street 7 Fort Collins, Larimer County, Colorado Project No.20075011 The stratification boundaries shown on ,the enclosed boring logs represent the approximate I_` locations of changes in soil types; in-situ, the transition of materials may be gradual. The subsurface soil, bedrock and groundwater conditions are presented on the Logs of BoringsA included in Appendix A of this report. L Field and Laboratory Test Results rThe native cohesive sandy lean clay stratum is medium stiff to very stiff in consistency and exhibits low swell potential and has low to moderate load bearing capabilities. Approximately 2 to r 9-1/2-feet of fill material was encountered in the test borings drilled for this study. We understand the majority of the fill material was placed during the demolition work of the previous fraternity house located on-site. Terracon personnel conducted field density, percent moisture content and compaction compliance testing procedures on a "part-time/as-needed" basis when called upon. For a summary of ou.r test results and findings, please refer to our Construction Materials Testing CMT) Project File No. 20061010. A summary of field density test results is also provided in Appendix B. Field tests indicate the fill material is generally stiff to very stiff in consistency and exhibits low to moderate swell potential, with one sample revealing a swell index value in excess iJ- 4 of 3-percent. Based upon the field penetration resistance values, in-situ dry densities, and the L laboratory consolidation test data, it appears the existing fill could be used for support of foundations, and floor slabs-on-grade without the need for removal or re-compaction. However, the consistency and relative density of the existing fill material must be verified prior to foundation, and slab-on-grade construction activities to assess that similar conditions exist across each footprint with those encountered in the test borings. I j- j Based on the review of our field and laboratory test data taken during the construction phase, it appears the fill material, where limited test results were taken; either met or exceeded the r minimum project specifications as required. Our test results represent only the materials at the location and time of testing. Terracon did not direct nor control the fill placement and compaction at the site and does not assume responsibility for the placement, compaction or control of the fill materials. Areas of fill, which are not representative of our testing, may exist throughout the backfilled zoned. It is the contractor's obligation/responsibility to coordinate with the testing firm to schedule the field density testing procedures as well as his responsibility to document the backfill zone was completed in general accordance with the project specifications. Swell—Consolidation Test Results The swell-consolidation test is commonly performed to evaluate the swell and/or collapse potentiali of soil or bedrock for determining foundation design criteria. In this test, relatively undisturbed 4 L J L Geotechnical Engineering Report 1rerra= IHellenic Plaza, Inc.1- 1 NANI/C of Shields Street and Birch Street Fort Collins, Larimer County,Colorado Project No.20075011 L. samples obtained directly from the ring barrel sampler are placed in a laboratory device and inundated under a predetermined load. The swell-index is the resulting amount of swell as aLpercentofthesample's thickness after the inundation period. Samples obtained at the 1 to 2-foot J intervals are generally pre-loaded and inundated with water at approximately 150 pounds per L square foot (PSF), to simulate the pavement conditions for the underlying subgrade materials. Samples obtained at the 3 to 4-foot intervals are generally pre-loaded and inundated with water at approximately 500 pounds per square foot (PSF), while samples obtained at the 7 to 9-foot intervals are pre-loaded and inundated with water at approximately 1,000 PSF to simulate overburden soils pressures. For this project we ran five swell-consolidation tests. The swell index values for the soil samples tested at the 150 psf, 500 psf, to 1,000-psf-inundation pressures, varied between approximately 0.2% to (+)3.2%. Copies of the swell-consolidation test results are presented in Appendix B of this report. Colorado'Association of Geotechnical Engineers(CAGE) uses the following information to provide uniformity in terminology between geotechnical engineers to provide a relative correlation of slab performance risk to measured swell. "The representative percent swell values are not necessarily measured values; rather, they are a judgment of the swell of the soil and/or bedrock profile likely to influence slab performance." Geotechnical engineers use this information to also evaluate the swell potential risks for foundation performance based on the risk categories. Recommended Representative Swell Potential Descriptions and Corresponding Slab Performance Risk Categories Representative Percent Swell Representative Percent SwellSlabPerformanceRiskCategory500psfSurcharge) 1000 psf Surcharge) Low Oto<3 Oto<2 Moderate 3 to<5 2 to<4 1 High 5to<8 4to<6 Very High 8 6 r r Based on the laboratory test results, the subsurface soils at the depths analyzed revealed low to moderate expansive potential. Groundwater Conditions Groundwater was not encountered in the test borings during our initial exploration nor when checked several days after drilling, to maximum depths of exploration. These observations 5 a a_ Geotechnical Engineering Report lrerracon Hellenic Plaza,Inc. NIW/C of Shields Street and Birch Street Fort Collins, Larimer County,Colorado Project No.20075011 represent groundwater conditions at the time of the field exploration, and may not be indicative of other times, or at other locations. ENGINEERING RECOMMENDATIONS Geotechnical Considerations The site appears suitable for the proposed construction from a geotechnical engineering point of i view. The presence of fill material was encountered across the site, which will require particular attention in the design and construction. It is important to establish and maintain good/positive surface drainage, especially in the immediate area of the proposed residential footprints during and after construction. The following foundation systems were evaluated for use on the site: Conventional type spread footings or continuous grade beams bearing on undisturbed soils with all footings extended to the lower foundation bearing stratum; or on approved engineered fill, (i.e. either imported low volume change soils or overexcavated subsoils replaced as engineered fill material). Basement construction is considered feasible for the site provided a complete dewatering system is placed around the basement area and construction recommendations presented herein are followed. Foundation Systems—Conventional Type Spread Footings It is our opinion the native subsoils and approved engineered fill material appear to be capable of supporting a foundation system designed using a net allowable bearing capacity of 2,000 psf. However, due to the variations of soils across the building footprint, (i.e. fill material consisting of lean clay or sandy lean clay with gravel, and native cohesive subsoils) at or near anticipated footing depths, as well as to minimize the potential for differential movement, it is recommended the entire the foundation bearing strata be scarified a minimum depth of 18-inches, moisture conditioned to near optimum moisture content and recompacted to 98 percent of Standard Proctor Density(SPD)ASTM D698. This will provide a more uniform zone beneath all footings, i.e., perimeter footing and interior column pads). All footings placed on a ground-modified native zone or engineered fill material should be designed for a net allowable bearing pressure I _ of 2,000 psf. In addition, all footings should be sized to maintain a minimum dead load pressure of 500 psf. An alternative to placement of the proposed structure on a ground- 6 Geotechnical Engineering Report Terracan Li Hellenic Plaza,Inc. N/W/C of Shields Street and Birch Street Fort Collins, Larimer County, Colorado Project No.20075011 modified bearing stratum would be to support the structure on a deep foundation system, of which design parameters will be provided upon request. Full-time quality control should be performed by Terracon to verify compliance to the project specifications. All footings should be placed on similar soils to reduce the potential forLJdifferentialmovementbetweensoiltypes. Quality control/field monitoring should include but not limited to moisture, density, compaction and lift thicknesses for the fill material being placed: Additional laboratory testing may be required based upon exposed subgrade/bearing strata materials. Exterior footings and foundations in unheated areasaeas must be protected from frost action. The normal depth of frost protection in this area is estimated to be around 30-inches. We recommend continuous wall footings have a width of at least 16-inches. Isolated column pads should have dimensions of at least 24-inches by 24-inches. Based upon the structural loading conditions provided, larger footing sizes will be needed to accommodate actual foundation load and design requirements. Ir In addition, it is imperative that positive drainage be maintained during construction and throughout the life of the facility to minimize the potential for surface water infiltration. It is Terracon's opinion that sub-excavation, if deemed necessary during a foundation excavation observation, and replacement with controlled fill combined with good positive drainage will minimize the settlement/expansive potential and will create a more stable bearing stratum. Exterior footings should be placed a minimum of 30-inches below finished grade for frost protection and to provide confinement for the bearingsoils. Finished grade is the lowest adjacent9adjacent grade for perimeter footings. Footings should be proportioned to reduce differential foundation movement. Proportioning9pPportornng on the basis of equal total movement is recommended; however, proportioning to relative constant dead-load pressure will also reduce differential movement between adjacent footings. Total movement resulting from the assumed structural loads is estimated to be on the order of about 1- inch. Additional foundation movements could occur if water from any source infiltrates the foundation soils; therefore, it is imperative proper drainage be provided in the final design and during construction for the structure. 7 L I 1:. Li Geotechnical Engineering Report lferracon Hellenic Plaza,Inc. 1 NIW/C of Shields Street and Birch Street Fort Collins, Larimer County,Colorado Project No. 20075011 iFoundation and walls should be reinforced as necessary to reduce the potential for distress caused by differential foundation movement. The use of joints at openings or other discontinuities in walls is recommended. Foundation excavations should be observed by the geotechnical Jengineer. If the soil conditions encountered differ significantly from those presented in this report, supplemental recommendations will be required. Fin.al recommendations during "open-hole" or foundation excavation observations may vary I'` depending upon conditions at that time, additional overlot grading procedures or design elevations. Foundation excavations should be observed by the geotechnical engineer. If the soil conditions encountered differ significantly from those presented in this report, supplemental recommendations will be required. 1 Basement Construction Groundwater was not encountered to maximum depths of exploration in any of the test borings m drilled for this study at this time. Therefore, full-depth basement construction is considered acceptable on the site provided a perimeter drainage system is installed around the lower levels. Perched groundwater may occur at times since the subsurface soils are relatively impermeable and tend to trap water. Completion of site development, including installation of landscaping and irrigation systems, may lead to perched groundwater development. To intercept the potential for surface water infiltration from impacting the foundation bearing stratum and entering the lower level in areas where the slabs are placed 4-feet or more above the groundwater levels, an exterior perimeter drainage is recommended. The exterior drainage system should be constructed around the exterior perimeter of the basement foundation, and c; sloped at a minimum 1/8 inch per foot to a suitable outlet, such as a sump and pump system. The exterior drainage system should consist of a properly sized perforated pipe, embedded in r free-draining gravel, and placed in a trench at least 12 inches in width. Gravel should extend a minimum of 3 inches beneath the bottom of the pipe, and at least 1-foot above the bottom of the foundation wall. The system should be underlain with a polyethylene moisture barrier, sealed to the foundation walls, and extending at least to the edge of the backfill zone. The gravel should be covered with drainage fabric prior to placement of foundation backfill. f.. . Lateral Earth Pressures For soils above any free water surface, recommended equivalent fluid pressures for H unrestrained foundation elements are: 8 ri; LI V JGeotechnical Engineering Report lferraron Hellenic Plaza,Inc. N/W/C of Shields Street and Birch Street Fort Collins, Larimer County, Colorado L Project No.20075011 L Active: Cohesive soil backfill (on-site clay soils) 45 psf/ft ICohesionless soil backfill(granular imported soils) 35 psf/ft r On-site bedrock materials not recommended for use Passive: L Cohesive soil backfill (on-site clay soils) 250 psf/ft 1 Cohesionless soil backfill (granular imported soils) 350 psf/ft L. 4i Drilled Piers 500 psf/ft Adhesion at base of footing 500 psf 61 Where the design includes restrained elements, the followingequivalent fluid pressures areq recommended: 171 o At rest: LI Cohesive soil backfill (on-site clay soils) 60 psf/ft Cohesionless soil backfill (granular imported soils) 50 psf/ft On-site bedrock materials not recommended for use The lateral earth pressures herein do not include any factor of safety and are not applicable for Isubmerged soils/hydrostatic loading. Additional recommendations may be necessary if submerged conditions are to be included in the design. i Fill against grade beams and retaining walls should be compacted to densities specified in Earthwork. Medium to high plasticity clay soils or claystone shale should not be used as backfill against retaining walls. Compaction'of each lift adjacent to walls should be accomplished with hand-operated tampers or other lightweight compactors. Overcompaction may cause excessive lateral earth pressures, which could result in wall movement.. r M Seismic Considerations i, .The project site is located in Seismic Risk Zone I of the Seismic Zone Map of the United States as indicated by the 1997 Uniform Building Code. Based upon the nature of the subsurface materials, Soil Profile Type "Sc" should be used for the design of structures for the proposed project (1997 q4. iy:4., 9 W Geotechnical Engineering Report lferracon Hellenic Plaza, Inc. 1 NAN/C of Shields Street and Birch Street Fort Collins, Larimer County,Colorado41_ Project No.20075011 Uniform Building Code, Table No. 16-J). A site classification "C" should be used for the design of structures for the proposed project(2003 International Building Code, Table No. 1615.1.1). Floor Slab Design and Construction The variability of the existing overburden soils in proximity to the upper and/or lower floor slab level subgrade elevations could result in differential movement of slabs should the low to moderate expansive materials become elevated in moisture content. If conventional-type slab on grade construction is utilized in these areas, differential slab movement on the order of 1 to 3 inches or more is possible. Therefore, positive drainage away from the building footprint to reduce the potential for surface water infiltration from impacting the underlying slab subgrade material should be implemented and maintained during and after construction activities. If slab 1 movement cannot be tolerated for-any proposed lower level slab, a structural floor system is recommended. Conventional-type slab-on-grade construction procedures are feasible for slabs, i provided the owner is willing is assume the risk for potential slab movement if the underlying subgrade materials become elevated in moisture content. As presented on the enclosed boring logs and laboratory test results, low to moderate expansive fill materials are present on this site. This report provides recommendations to help mitigate the effects of soil shrinkage or expansion: Even if these procedures are followed, some movement and at least minor cracking in the structure should be anticipated. The severity of cracking and other cosmetic damage such as uneven floor slabs will probably increase if any modification of the site results in excessive wetting or drying of the expansive materials. Eliminating the risk of movement and cosmetic distress may not be feasible, but it may be possible to further reduce the risk of movement if significantly more expensive measures are used during construction. Some of these options, such as the use of structural floors or overexcavating and replacing expansive materials are discussed in this report. We would be pleased to discuss other construction alternatives with you upon request. J: Additional floor slab design and construction recommendations are as follows: e Positive separations and/or isolation joints should be provided between slabs and all foundations, columns or utility lines to allow independent movement. Control joints should be provided in slabs to control the location and extent of cracking. 10 i Lf 1 L Geotechnical Engineering Report lferracon L Hellenic Plaza,Inc. N/W/C of Shields Street and Birch Street Fort Collins,Larimer County, Colorado 4 Project No.20075011 A minimum 2-inch void space should be constructed above or below non-bearing L.: partition walls placed on slabs on grade. Special framing details should be provided at doorjambs and frames within partition walls to avoid potential distortion. Partition walls should be isolated from suspended ceilings. Lie Interior rtench backfill placed beneath slabs should be compacted in accordance rwith recommended specifications outlined below. In areas subjected to normal loading, a minimum 4-inch layer of clean-graded gravel or aggregate base course should be placed beneath upper level interiorLslabs. A minimum 8-inch -layer of free-draining gravel should be placed beneath basement floor slabs in conjunction with the undersiab drainage system. L. 4 Floor slabs should not be constructed on frozen subgrade. Other design and construction considerations, as outlined in the ACI Design Manual, Section 302.1 R are recommended. Pavement Design and Construction (For Non-Jurisdictional On-Site Areas)L • Based on the subsurface conditions encountered during the site exploration, it is our opinion theLproposedon-site pavement areas are feasible provided the following recommendations are implemented. The subsoils encountered throughout the site are generally plastic/cohesive soils a exhibiting low subgrade strength characteristics and low to moderate swell/expansive potential. This report provides recommendations to help mitigate the effects of soil shrinkage and expansion. Even if these recommendations are followed some pavement distress and exterior Li--- slab movement should be anticipated. j Relatively undisturbed subsurface samples obtained at anticipate pavement subgrade elevations, revealed swell-index values less than 2-percent when inundated with water and pre-loaded at 150 psf in accordance with Larimer CountyUrban Area Street Standards(LCUSS)(S) Pavement Design LJ Criteria, a guideline used to evaluate the pavement design recommendations. Swell-index test results in excess of 2-percent when inundated with water at a pre-loading scheme of 150 psf I would generally require a swell mitigation plan. Based on our experience with similar soil i_ conditions and the nature of the subsurface soil on-site, subgrade stabilization may be necessary 1 11 c._ G jP TJ ik Geotechnical Engineering Report liierrazon Hellenic Plaza,Inc. NIW/C of Shields Street and Birch Street l Fort Collins, Larimer County,Colorado x`'. Project No.20075011 1 a`,3 prior to pavement procedures. Depending upon the time of year of construction and approvalj process of a passing subgrade proof roll, consideration should be given to a fly ash treatmenttli: procedure. If necessary, a fly ash treatment procedure should be incorporated into the subgrade I section as a stabilization method to enhance the integrity of the underlying subsoils prior to 41 placement of base course or Hot Mix Asphalt(HMA) materials. The LCUASS Pavement Design Criteria provides guidelines for consultants conducting pavement a evaluation assessments when subgrade stabilization is necessary. This may include incorporation of a chemical treatment such as kiln dust, and/or fly ash to reduce the swell potential a or an over:excavation and replacement with two-feet of non-to low expansive type soils. Due to I the potential pumping conditions, which develop in a moisture treatment process, we recommend r : 1 the use of fly ash. i Incorporating into the upper 12-inches of the rough final subgrade soils with the use of a chemical treatment rocess, such as flyash is recommended for this,: { p project. Proofrolling and m" recompacting the subgrade is recommended immediately prior to placement of the aggregate road base section. Soft or weak areas delineated by the proofrolling operations should be 9' 1 undercut or stabilized in-place to achieve the appropriate subgrade support with additional fly ashy if necessary. u. Asphalt concrete underlain by crushed aggregate base course with or without a fly ash treated subgrade, and non-reinforced concrete pavement are feasible alternatives for the proposed on- site paved sections. Based on the subsurface conditions encountered at the site, and the laboratory test results, it is recommended the on-site private drives and parking areas be irc.designed using a minimum R-value of 7. i 7 tE wr'Pavement design methods are intended to provide structural sections with adequate thickness over a particular subgrade such that wheel loads are reduced to a level the subgrade can support. The support characteristics of the subgrade for pavement design do not account for shrink/swell movements of an expansive clay subgrade such as the soils encountered on this project. Thus, the pavement may be adequate from a structural standpoint, yet still experience cracking and L deformation due to shrink/swell related movement of the subgrade. It is, therefore, important to minimize moisture changes in the subgrade to reduce shrink/swell movements. kEr .. t Recommended alternatives for flexible and rigid pavements, summarized for each traffic area, are it as follows: J 12 it iaW L- i.. i Geotechnical Engineering Report lferraton Hellenic Plaza, Inc. NMI/C of Shields Street and Birch Street Fort Collins,Larimer County,Colorado Project No.20075011 RECOMMENDED MINIMUM PAVEMENT THICKNESS-INCHES Traffic Area Alternatives I)Asphalt Asphalt Concrete Aggregate Base (2) Fly Ash Treated Portland Concrete Surface Surface Grading Course-Class Cement Total i Grading SX S or SG 5 or 6 Sub Base Concrete 3)A 1.5 2.5 6.0 10.0 Automobile B 3.5 6.0 12.0 21.5 Parking Areas C-1 6.0 6.0 C-2 12.0 5.5 17.5 f 3)A 1.5 2.5 8.0 12.0 4 Heavy Duty/Truck B 1.5 2.5 6.0 12.0 22.0 Traffic Areas C-1and/or Fire Lane 7.0 7.0 C-2 12.0 6.0 18.0 J 1) If the asphalt surface course is to consist of Grading S, then the required minimum lift/thickness placed should be 2-inches. If the asphalt surface course is to consist of Grading SX, the required minimum lift/thickness placed should be 1-1/2-inches.i 2) If fly ash is utilized for the on-site pavement improvement areas to stabilize the subgrade materials, it is recommended that at least the upper 12-inches of the prepared subgrade be treated with fly ash. Terracon is available to provide the required laboratory soil and fly ash i mix design as well as placement recommendations upon request. 3) Alternative A assumes a minimum of 2-feet of overexcavated, moisture 1 conditioned/processed, and re-compacted subgrade material is positioned beneath the planned paved sections, and an approved proof-roll has been completed. r j Due to the properties of the existing cohesive on-site soils, full depth asphalt pavement is not recommended. Each alternative should be investigated with respect to current material availability and economic conditions. Aggregate base course (if used on the site) should consist of a blend of sand and gravel, which meets strict specifications for quality and gradation. Use of materials meeting 1 Colorado Department of Transportation (CDOT) Class 5 or 6 specifications is recommended for base course. Aggregate base course should be placed in lifts not exceeding six inches and should be compacted to a minimum of 95% Standard Proctor Density(ASTM D698). Asphalt concrete pavement should be composed of a mixture of aggregate, filler, binders, and additives, if required, and approved bituminous material in accordance with the LCUASS Pavement Design Criteria. The asphalt concrete should conform to an approved mix design 13 i t f I JII. Geotechnical Engineering Report lferracon Hellenic Plaza,Inc. N/W/C of Shields Street and Birch Street Fort Collins,Larimer County,Colorado Project No.20075011 stating the Hveem and/or Superpave properties, optimum asphalt content, job mix formula and recommended mixing and placing temperatures. Aggregate used in the asphalt concrete should meet particular gradations, such as the Colorado Department of Transportation Grading S, SX or SG specifications. Mix designs should be submitted prior to construction to verify their adequacy. Asphalt material should be placed in maximum 3-inch lifts and should be compacted to a within a range of 92 to 96% of Maximum Theoretical Density. For areas subject to concentrated and repetitive loading conditions such as dumpster pads, truck delivery docks and ingress/egress aprons, we recommend using a Portland cement concrete pavement with a thickness of at least 7 inches underlain by at least 4 inches of aggregate road base material. Prior to placement of the aggregate road base material, the areas should be thoroughly proofrolled. For dumpster pads, the concrete pavement area should be large enough to support the container and tipping Ale of the refuse truck. Long term pavement performance will be dependent upon several factors, including maintaining subgrade moisture levels and providing for preventive maintenance. The following recommendations should be considered the minimum: Site grading at a minimum 2% grade away from the pavements; The subgrade and the pavement surface have a minimum 1/4 inch per foot slope to promote I proper surface drainage. Consider appropriate edge drainage and pavement under drain systems,rj Install pavement drainage surrounding areas anticipated for frequent wetting (e.g. garden centers, wash racks) Install joint sealant and seal cracks immediately, Seal all landscaped areas in, or adjacent to pavements to minimize or prevent moisture migration to subgrade soils; Placing compacted, low permeability backfill against the exterior side of curb and gutter; and, Placing curb, gutter and/or sidewalk directly on subgrade soils with the use of base course materials beneath. IL Preventive maintenance should be planned and provided for through an on-going pavement management program. Preventive maintenance activities are intended to slow the rate of pavement deterioration, and to preserve the pavement investment. Preventive maintenance consists of both localized maintenance (e.g. crack and joint sealing and patching) and global maintenance (e.g. surface sealing). Preventive maintenance is usually the first priority when implementing a planned pavement maintenance program and provides the highest return on V ; 14 li } L_ Geotechnical Engineering Report lrerracon Hellenic Plaza, Inc. NIW/C of Shields Street and Birch Street Fort Collins, Larirner County,Colorado Project No.20075011 investment for pavements. Prior to implementing any maintenance, additional engineering observation is recommended to determine the type and extent of preventive maintenance. Site grading is generally accomplished early in the construction phase. However as construction proceeds, the subgrade may be disturbed due to utility excavations, construction traffic, desiccation, or rainfall. As a result, the pavement subgrade may not be suitable for pavement construction and corrective action will be required. The subgrade should be carefully evaluated at the time of pavement construction for signs of disturbance or excessive rutting. If disturbance has occurred, pavement subgrade areas should be reworked, moisture conditioned, and properly compacted to the recommendations in this report immediately prior to paving. Please note that if during or after placement of the stabilization or initial lift of pavement, the area is observed to be yielding under vehicle traffic or construction equipment, it is recommended that Terracon be contacted for additional alternative methods of stabilization, or a change in the pavement section. Earthwork General Considerations The following presents recommendations for site preparation, excavation, subgrade preparation and placement of engineered fills on the project. All earthwork on the project should be observed and evaluated by Terracon. The evaluation of earthwork should include observation and testing of engineered fill, subgrade preparation, foundation bearing soils, and other geotechnical conditions exposed during the construction of the project. j Site Preparation Strip and remove any existing vegetation, debris or other deleterious materials from proposed building and pavement areas. All exposed surfaces should be free of mounds and depressions that could prevent uniform compaction. The site should be initially graded to create a relatively level surface to receive fill, and to J provide for a relatively uniform thickness of fill beneath proposed building addition. Demolition of the existing single family residential structure on the northern portion of the site should include complete removal of all foundation systems within the proposed construction area. This should include removal of any loose backfill found adjacent to 15 L L Geotechnical Engineering Report lferraron L Hellenic Plaza, Inc. N/W/C of Shields Street and Birch Street Fort Collins,Larimer County,Colorado Li: Project No.20075011 existing foundations. All materials derived from the demolition of existing structures and pavements should be removed from the site and not be allowed for use in any on-siteLfills. i i Although evidence of underground facilities such as septic tanks, cesspools, Lbasements, and utilities was not observed during the site reconnaissance, such features could be encountered during construction. If unexpected fills, beyond that previously I--1 described herein, or underground facilities are encountered, such features should be removed and the excavation thoroughly cleaned prior to backfill placement and/or construction. F It is anticipated that excavations for the proposed construction can be accomplished with conventional earthmoving equipment. Li-Exposed areas, which will receive fill, once properly cleared where necessary, should be scarified to a minimum depth of 12-inches, conditioned to near optimum moisture content, j and compacted. The stability of the subgrade may be affected by precipitation, repetitive construction traffic or other factors. If unstable conditions develop, workability may be improved by scarifying L:and drying. Overexcavation of wet zones and replacement with granular materials may be necessary. Use of lime, fly ash, kiln dust, cement or geotextiles could also be considered 1 i as a stabilization technique. Laboratory evaluation is recommended to determine the effect of chemical stabilization on subgrade soils prior to construction. Lightweight ii excavation equipment may be required to reduce subgrade pumping. Subgrade Preparation Subgrade soils beneath interior and exterior slabs and beneath pavements should be scarified; moisture conditioned and compacted to a minimum depth of 12-inches. The 1 moisture content and compaction of subgrade soils should be maintained until slab or pavement construction. H a Fill Materials and Placement Approved imported materials may be used as fill material and are suitable for use as t compacted fill beneath interior or exterior floor slabs. 16 L_ i r Geotechnical Engineering Report lfercacon Hellenic Plaza,Inc. N/W/C of Shields Street and Birch Street Fort Collins, Larimer County,Colorado Project No.20075011 I Imported soils (if required)should conform to the following: Percent finer by weight Gradation ASTM C136) ir 3.. 100 No. 4 Sieve 50-100 I No. 200 Sieve 35 (max) 4 i Liquid Limit 30 (max) 1--- Plasticity Index 15 (max) Group Index 10(max) Engineered fill should be placed and compacted in horizontal lifts, using equipment and procedures that will produce recommended moisture contents and densities throughout the lift. It is recommended all fill material to placed on the site be compacted to at least 95 percent of Standard Proctor Density ASTM D698, with the exception of therfoundationbearingstrataat98percentSPDminimum. s On-site clay soils should be compacted within a moisture content range of 1 percent below, to 3 percent above optimum. Imported granular soils should be compacted within a 4." moisture range of 3 percent below to 3 percent above optimum unless modified by the project geotechnical engineer. Excavation and Trench Construction Excavations into the on-site soils will encounter a variety of conditions. Excavations into i the clays can be expected to stand on relatively steep temporary slopes during construction. However, caving soils and groundwater may also be encountered. The individual contractor(s) should be made responsible for designing and constructing stable, z, i temporary excavations as required to maintain stability of both the excavation sides and bottom. All excavations should be sloped or shored in the interest of safety following local and federal regulations, including current.OSHA excavation and trench safety standards. The soils to be penetrated by the proposed excavations may vary significantly across the site. The preliminary soil classifications are based solely on the materials encountered in widely spaced exploratory test borings. The contractor should verify that similar conditions exist throughout the proposed area of excavation. If different subsurface conditions are 17 rk7 _ L Geotechnical Engineering Report Terra=an Hellenic Plaza, Inc. N!WIC of Shields Street and Birch Street Fort Collins,Larimer County,Colorado Project No.20075011 encountered at the time of construction, the actual conditions should be evaluated to determine any,excavation modifications necessary to maintain safe conditions. As a safety measure, it is recommended that all vehicles and soil piles be kept to a minimum lateral distance from the crest of the slope equal to no less than the slope height. The exposed slope face should be protected against the elements. Additional Design and Construction Considerations Exterior Slab Design and Construction Compacted subgrade or existing clay soils will expand with increasing moisture content; therefore, exterior concrete grade slabs may heave, resulting in cracking or vertical offsets. The potential for damage would be greatest where exterior slabs are constructed adjacent to the building or other structural elements. To reduce the potential for damage, we recommend: exterior slabs be supported on fill with no, or very low expansion potential strict moisture-density control during placement of subgrade fills placement of effective control joints on relatively close centers and isolation joints between slabs and other structural elements provision for adequate drainage in areas adjoining the slabs use of designs which allow vertical movement between the exterior slabs and adjoining structural elements r` In those locations where movement of exterior slabs cannot be tolerated or must be reduced, consideration should be given to: Constructing slabs with a stem or key-edge, a minimum of 6 inches in width and at least 12 inches below grade; supporting keys or stems on drilled piers; or providing structural exterior slabs supported on foundations similar to the building. Corrosion Protection Results of soluble sulfate testing indicate that ASTM Type I Portland cement is suitable for all concrete on and below grade. However, if there is no, or minimal cost differential, use of ASTM Type II Portland cement is recommended for additional sulfate resistance of 18 L Geotechnical Engineering Report Turman L— Hellenic Plaza, Inc. N/W/C of Shields Street and Birch Street Fort Collins, Larimer County, Colorado Project No.20075011 construction concrete. Foundation concrete should be designed in accordance with the provisions of the ACI Design Manual, Section 318, Chapter 4. Under ro n•g u d Utility Systems All piping should be adequately bedded for proper load distribution. It is suggested that clean, graded gravel compacted to 75 percent of Relative Density ASTM D4253 be used as bedding. Depending upon the depth of excavation, groundwater may be encountered. Contractors should be prepared to dewater trenches at the site. Utility trenches should be excavated on safe and stable slopes in accordance with OSHA regulations as discussed above. Backfill should consist of the on-site soils or imported material approved by the geotechnical engineer. The pipe backfill should be compacted to a minimum of 95 percent of Standard Proctor Density ASTM D698. Surface Drainage Positive drainage should be provided during construction and maintained throughout the life of the proposed project. Infiltration of water into utility or foundation excavations must be prevented during construction. Planters and other surface features, which could retain water in areas adjacent to the building or pavements, should be sealed or eliminated. In areas where sidewalks or paving do not immediately adjoin the structure, we recommend that protective slopes be provided with a minimum grade of approximately 10 percent for at !east 10 feet from perimeter walls. Backfill against footings, exterior walls, and in utility and sprinkler line trenches should be well compacted and free of all construction debris to reduce the possibility of moisture infiltration. Downspouts, roof drains or scuppers should discharge into splash blocks or extensions when the ground surface beneath such features is not protected by exterior slabs or paving. Sprinkler systems should not be installed within 10-feet of foundation walls. Landscaped irrigation adjacent to the foundation system should be minimized or eliminated. GENERAL COMMENTS Terracon should be retained to review the final design plans and specifications so comments can be made regarding interpretation and implementation of our geotechnical recommendations in the design and specifications. Terracon also should be retained to provide testing and observation during excavation, grading, foundation and construction phases of the project. 19 tvr4- ri i Geotechnical Engineering Report lferracon Hellenic Plaza,Inc. Nm/C of Shields Street and Birch Street Ma, I Fort Collins, Larimer County,Colorado y Project No.20075011 L. The analysis and recommendations presented in this report are based upon the data obtained 4"c J from the borings performed at the indicated locations and from other information discussed in this a report. This report does not reflect variations that may occur between borings, across the site, orie 4.°yi due to the modifying effects of weather. The nature and extent of such variations may not become evident until during or after construction. If variations appear, we should be immediatelyV' notified so that further evaluation and supplemental recommendations can be provided. r htr' The scope of services for this project does not include either specifically or by implication anyi' uP ', environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or p,' prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the 11Pr °, potential for such contamination or pollution, other studies should be undertaken. This report has been prepared for the exclusive use of our client for specific applicationpppcation to thedi" project discussed and has been prepared in accordance with generally accepted geotechnical 1, engineering practices. No warranties, either express or implied, are intended or made. Site 1 ' I4— safety, excavation support, and dewatering requirements are the responsibility of others. In the event that changes in the nature, design, or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered Vloil valid unless Terracon reviews the changes and either verifies or modifies the conclusions of this Ifs report in writing. II , f,t i ' 1 t. q -" 20 1 V: I:il l 01 ail:--1 j i tWILL]! r: . MCLANC MO— 8 z i,::'-!'.:- N w teP-#4 TBM I I Alai= o 71.1irl- I 11 1111111 I I = M pig , tYi I if! I 011 I UILWILH r) f 30' WIDE FIRE LANE 7 / O w ii' ;.,•. i 4 T TII 7 T TITI I I I I Is 4. 6II , I i ar.i. Nii I;, E_y r.. BIRCH STREET v II":, lirL LEGEND T.B. Nos: 1 -4, FOUNDATION RELATED I TEST BORINGS. It , T.B. Nos.5-8, PAVEMENT RELATED TEST BORINGS. TBM, (TEMPORARY BENCH MARK), N/W PROPERTY PIN, ASSUME ELEV.= 100.0' r FIGURE 1;SITE DIAGRAM&TEST BORING LOCATIONS HELLENIC PLAZA P.O.D. k "" NIW/C BIRCH STREET&S.SHIELDS STREET FORT COLLINS,COLORADO Project Mngr DAR Project No I}e"20075011 DesignedY r Checked By: Date: DAR 301 N.Howes Street 02/26/07 Approved By: DAR Fort Collins,Colorado 80521 Drawn By: DJS DIAGRAM IS FOR GENERAL LOCATION ONLY. AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES. Fle Name: 20075011-1 Rage No. 1 /