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HomeMy WebLinkAboutHICKORY COMMONS - FDP - FDP130014 - SUBMITTAL DOCUMENTS - ROUND 1 - RECOMMENDATION/REPORTGEOTECHNICAL SUBSURFACE EXPLORATION REPORT HICKORY STREET LIVE/WORK UNITS 1-ACRE PARCEL WEST OF COLLEGE AVENUE SOUTH OF HICKORY STREET FORT COLLINS, COLORADO EEC PROJECT NO. 1102069 Prepared for: MTA Planning & Architecture 171 North College Avenue Fort Collins, Colorado 80524 Attn: Mr. Troy Jones, AICP Prepared by: Earth Engineering Consultants, Inc. 4396 Greenfield Drive Windsor, Colorado 80550 4396 GREENFIELD DRIVE WINDSOR, COLORADO 80550 (970) 545-3908 FAX (970) 663-0282 November 11, 2010 MTA Planning & Architecture 171 North College Avenue Fort Collins, Colorado 80524 Attn: Mr. Troy Jones, AICP Re: Geotechnical Subsurface Exploration Report Hickory Street Live/Work Units Approximate 1-Acre Parcel west of College Avenue and south of Hickory Street Fort Collins, Colorado EEC Project No. 1102069 Mr. Jones: Enclosed, herewith, are the results of the geotechnical subsurface exploration for the proposed Hickory Street Live/Work Units development project planned for construction on the south side of Hickory Street, west of College Avenue in north Fort Collins, Colorado. We understand this project involves the construction of five (5) approximately 5,000 square feet, 2-story metal framed, slab-on- grade buildings on an approximate 1-acre lot, along with associated on-site pavement areas. Also included will be an approximate 200 linear feet of roadway widening/improvements along Hickory Street to accommodate access into the property, which will be required to meet City of Fort Collins standards. This study was completed in general accordance with our proposal dated September 21, 2010. In summary, the subsurface materials encountered in the four (4) soil borings, two (2) of which were drilled within the proposed on-site development areas, and two (2) were drilled within the proposed roadway improvement along Hickory Street, completed at this site in October of 2010, consisted of cohesive native and/or fill materials classified as sandy lean clay and silty, clayey sand extending to the fine to coarse granular strata below. Silty sand and silty sand with gravel and intermittent cobbles were encountered below the upper cohesive soils in each boring at approximate depths of 4 to 9-feet below site grades and extended to the depths explored, approximately 10 to 15- feet below site grades. Groundwater was encountered in the three (3) deeper borings, (i.e., borings B-1 through B-3, which were drilled to depths of 15-feet) at approximate depths of 5 to 10-feet below existing site grades. In review of the field and laboratory test results, we observed the upper portion of the cohesive subsoils within the roadway alignment exhibited slightly drier in-situ moisture contents along with GEOTECHNICAL SUBSURFACE EXPLORATION REPORT HICKORY STREET LIVE/WORK UNITS 1-ACRE PARCEL WEST OF COLLEGE AVENUE SOUTH OF HICKORY STREET FORT COLLINS, COLORADO EEC PROJECT NO. 1102069 November 11, 2010 INTRODUCTION The subsurface exploration for the proposed Hickory Street live/work units development project planned for construction on the south side of Hickory Street and west of College Avenue in north Fort Collins, Colorado has been completed. For this study a total of four (4) soil borings were completed within the development area to obtain information on existing subsurface conditions. The borings were extended to depths of approximately 10 to 15-feet below present site grades. Tow (2) of these borings wee located and drilled within the proposed development parcel and the remaining two (2) borings were located and drilled within the proposed widening improvements along Hickory Street. Individual boring logs and a site diagram indicating the approximate boring locations are provided with this report. We understand this project involves the construction of five (5) approximately 5,000 square feet, 2-story metal framed, slab-on-grade buildings on an approximate 1-acre lot, along with associated on-site and off-site pavement improvements. The proposed improvements along Hickory Street are necessary to provide access into the property and will be required to meet City of Fort Collins standards, (i.e., Larimer County Urban Area Street Standards) pavement design criteria. We anticipate maximum wall and column loads for the proposed buildings, will be on the order of 1 to 4 klf and 25 to 100 kips respectively. If these loading conditions vary significantly, we should be consulted to re-evaluate the foundation design recommendations as presented herein. Floor loads are expected to be light. Adjacent to the building footprint will be associated pavement areas to accommodate the anticipated traffic flow and parking. On-site pavement traffic is expected to include predominately automobiles in most areas and possibly heavier truck traffic in limited/loading areas. Off-site pavement improvements along Hickory Street, classified as an industrial/commercial collected will be necessary to accommodate access into the property. Minor grade changes are expected to develop final site grades. Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 2 The purpose of this report is to describe the subsurface conditions encountered in the borings, analyze and evaluate the test data and provide geotechnical recommendations concerning design and construction of the foundations, support of floor slabs, and on-site and off-site pavements. Those recommendations are based, in part, on discussions with the project owner and/or project design team. EXPLORATION AND TESTING PROCEDURES The boring locations were determined and established in the field by a representative of Earth Engineering Consultants, Inc. (EEC) by pacing and estimating angles from identifiable site features. The locations of the on-site borings were located within areas accessible to our drilling equipment adjacent to and/or in between various soil stockpiles positioned throughout the site, as shown on the enclosed site photographs. The location for each boring should be considered accurate only to the degree implied by the methods used. Photographs of the site, taken at the time of drilling, are also provided with this report. The borings were performed using a truck mounted, CME-75 drill rig equipped with a hydraulic head employed in drilling and sampling operations. The boreholes were advanced using 4-inch nominal diameter continuous flight augers. Samples of the subsurface materials encountered were obtained using split-barrel and California barrel sampling techniques in general accordance with ASTM Specification D-1586. In the split-barrel and California barrel sampling procedures, standard sampling spoons are driven into the ground by means of a 140-pound hammer falling a distance of 30 inches. The number of blows required to advance the samplers is recorded and is used to estimate the in-situ relative density of cohesionless materials and, to a lesser degree of accuracy, the consistency of cohesive soils and hardness of weathered bedrock. Relatively undisturbed samples are obtained in the California sampler. All samples obtained in the field were sealed and returned to the laboratory for further examination, classification, and testing. Moisture content tests were performed on each of the recovered samples. In addition, the unconfined strength of appropriate samples was estimated using a calibrated hand penetrometer. Washed sieve analysis and Atterberg limits tests were completed on selected samples to evaluate Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 3 the quantity and plasticity of the fines in the subgrade soils. Swell/consolidation tests were completed on selected samples to evaluate the tendency of the soil to change volume with variation in moisture content and load. A Hveem Stabilometer/R-Value was performed on a composite subgrade samples obtained within the Hickory Street pavement borings to evaluate subgrade strength characteristics in general accordance with LCUASS pavement design criteria. Results of the outlined tests are indicated on the attached boring logs and summary sheets. As a part of the testing program, all samples were examined in the laboratory by an engineer and classified in accordance with the attached General Notes and the Unified Soil Classification System based on the texture and plasticity of the soil. The estimated group symbol for the Unified Soil Classification System is indicated on the boring logs. A brief description of the Unified Soil Classification System is included with this report. SITE AND SUBSURFACE CONDITIONS The proposed Hickory Street live/work units development site is located on the south side of Hickory Street west of College Avenue on an approximate 1-acre undeveloped parcel of land. The property is partially bounded by chain link, with established commercial property to the east and west. The site is sparsely vegetated with deciduous trees along the northern portion and as shown on the site photographs various soil stockpiles were positioned throughout the middle and southern portions. The site is relatively flat exhibiting positive/fair surface drainage in the south direction. An EEC field engineer was on site during drilling to evaluate the subsurface conditions encountered and supervise the drilling activities. Field logs prepared by EEC site personnel were based on visual and tactual observation of disturbed samples and auger cuttings. The final boring logs included with this report may contain modifications to the field logs based on the results of laboratory testing and evaluation. Based on the results of the field borings and laboratory evaluation, subsurface conditions can be generalized as follows. In summary, the subsurface materials encountered in the four (4) soil borings, two (2) of which were drilled within the proposed on-site development areas, and two (2) were drilled within the proposed roadway improvement along Hickory Street, consisted of cohesive native and/or fill Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 4 materials classified as sandy lean clay and silty, clayey sand extending to the fine to coarse granular strata below. Silty sand and silty sand with gravel and intermittent cobbles were encountered below the upper cohesive soils in each boring at approximate depths of 4 to 9-feet below site grades and extended to the depths explored, approximately 10 to 15-feet below site grades. The upper cohesive soils encountered beneath the surficial layer within the roadway/Hickory Street related pavement borings varied from medium stiff to very stiff in consistency and exhibited low to moderate swell potential, while the cohesive subsoils within the development portion of the site revealed slight soft/compressible conditions and relatively low bearing capacity characteristics. Swell potential of the Hickory Street subgrade samples were approximately 2.8% to 4.1% when loaded and inundated with water utilizing the LCUASS 150 psf loading scheme, while the on-site subsoils at or near anticipated foundation bearing zones and/or encroaching the groundwater level, revealed soft/compressible conditions. The results of the swell-consolidation tests are presented in the Appendix of this report. The granular subsoils encountered at increased depths as shown on the enclosed borings logs were medium dense to dense and exhibited moderate load bearing characteristics. The stratification boundaries indicated on the boring logs represent the approximate locations of changes in soil types. In-situ, the transition of materials may be gradual and indistinct. GROUNDWATER CONDITIONS Observations were made while drilling and after completion of the borings to detect the presence and depth to hydrostatic groundwater. At the time of drilling, groundwater was encountered in the three (3) deeper borings, (i.e., borings B-1 through B-3, which were drilled to depths of 15- feet) at approximate depths of 5 to 10-feet below existing site grades. Groundwater depths are shown on the top right hand portion of the enclosed boring logs. Fluctuations in groundwater levels can occur over time depending on variations in hydrologic conditions, and other conditions not apparent at the time of this report. Longer term monitoring of water levels in cased wells, which are sealed from the influence of surface water would be required to more accurately evaluate fluctuations in groundwater levels at the site. We have typically noted Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 5 deepest groundwater levels in late winter and shallowest groundwater levels in mid to late summer. Zones of perched and/or trapped water can be encountered at times throughout the year in more permeable zones in the subgrade soils and perched water is commonly observed in subgrade soils immediately above lower permeability bedrock. ANALYSIS AND RECOMMENDATIONS Swell – Consolidation Test Results The swell-consolidation test is commonly performed to evaluate the swell or consolidation potential of soils for determining foundation, floor slab and pavement design criteria. In this test, relatively undisturbed samples obtained directly from the ring barrel sampler are placed in a laboratory apparatus and inundated with water under a predetermined load. The swell-index is the resulting amount of swell or collapse as a percent of the sample’s thickness after the inundation period. Samples obtained at approximate depths of 1 to 2-feet are generally pre-loaded at 150-psf to simulate the floor and pavement loading conditions, (i.e., as per LCUASS guidelines), while samples obtained at the 3 to 4-foot intervals are pre-loaded at 500 psf to simulate the overburden soil pressure at anticipated foundation depths. All samples are inundated with water and monitored for swell and consolidation. After the inundation period, additional incremental loads are applied to evaluate the swell pressure and/or of consolidation. For this assessment, we conducted four (4) swell-consolidation tests at various intervals/depths throughout the site. The swell index values for the samples analyzed for pavement design criteria, (i.e., soil samples obtained within borings B-3 and B-4 within the planned Hickory Street roadway improvements and tested at the 150 psf-inundation pressure), revealed low to moderate swell characteristics on the order of (+) 2.8% to 4.1%, excess of the maximum allowable swell-index value of 2% established within the LCUASS guidelines. The swell index values for the upper level cohesive samples analyzed for foundation design criteria, (i.e., soil samples obtained within borings B-1 and B-1 within the upper 4-feet and tested at the 500 psf-inundation pressure), revealed non to low swell characteristics, and slight compressible conditions with results on the order of (-) 0.1 to (- ) 0.3%. These swell –consolidation results also revealed a slight tendency to consolidate. The (-) test results indicate the tendency to consolidate upon inundation with water, while the (+) test results indicate the swell potential characteristics. Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 6 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 Slab Performance Risk Category Representative Percent Swell (500 psf Surcharge) Representative Percent Swell (1000 psf Surcharge) Low 0 to < 3 0 < 2 Moderate 3 to < 5 2 to < 4 High 5 to < 8 4 to < 6 Very High > 8 > 6 Based on the laboratory test results, the samples analyzed for this project were within the low range. General Considerations General Site Preparation Based on our understanding of the proposed development, it appears minor amounts of cut and/or fill may be necessary to achieve final design grades. After stripping and completing all cuts and prior to placement of any additional fill and/or site improvements, we recommend the exposed soils be scarified to a minimum depth of 9 inches, adjusted in moisture content to within ±2% of standard Proctor optimum moisture content and compacted to at least 95% of the material's standard Proctor maximum dry density as determined in accordance with ASTM Specification D- 698. Depending upon depth of excavation across the site, areas of soft/compressible cohesive soils at or near the groundwater levels may require ground modifications/ground stabilization procedures Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 7 to create a working platform or stable subgrade. If necessary, consideration could be given to placement of a granular material, such as a 3-inch minus recycled concrete or equivalent, embedded into the soft soils, prior to placement of additional fill material, foundations, or operating heavy earth-moving equipment. Supplemental recommendations, such as overexcavation and replacement with approved on-site soils or imported fill, will be evaluated at time of construction, as-needed. Fill materials required for developing the on-site building footprints areas, all pavement areas, and on-site subgrades should consist of approved, low-volume-change materials, which are free from organic matter and debris. It is our opinion the on-site cohesive soils could be used as fill in these areas, provided adequate moisture treatment and compaction procedures are followed. We recommend the fill soils be placed in loose lifts not to exceed 9 inches thick and adjusted in moisture content and compacted as recommended for the scarified soils. If the site lean clay soils are used as fill material, care will be needed to maintain the recommended moisture content prior to and during construction of overlying improvements. In areas where excavations will extend below existing groundwater table, such as deep utility installations, placement of cleaner granular fill material may be desirable. Those materials should be placed in lifts and compacted to at least 70% relative density, where applicable. Care should be exercised after preparation of the subgrades to avoid disturbing the subgrade materials. Positive drainage should be developed away from the structures to avoid wetting of subgrade materials. Subgrade materials becoming wet subsequent to construction of the site structures can result in unacceptable performance. As presented on the enclosed boring logs and laboratory test results, low to moderate swelling cohesive soils are present on this site within the Hickory Street roadway pavement alignment, while soft/compressible subsoils at increased depths at or near the groundwater levels were encountered within the proposed building footprints. This report provides recommendations to help mitigate the effects of soil expansion and/or consolidation. Even if these procedures are followed, some movement and at least minor cracking in the structures 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 site soils. Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 8 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 over-excavating and replacing site materials are discussed in this report. We would be pleased to discuss other construction alternatives including drilled piers and structural floors with you upon request. Foundation Systems – General Considerations The site appears suitable for the proposed construction based on the results of our field exploration and review of the proposed development plans. The following foundation system was evaluated for use on the site with the understanding of a slab-on-grade structure. • For slab-on-grade construction bearing within the upper level cohesive soils conventional type spread footings bearing on ground modified on-site subsoils or on engineered/controlled fill materials are suitable for use. Particular attention will be required during the supplemental site observations, such as “open-hole” or foundation excavation observations to further assess the soil conditions and foundation design bearing strata for each building footprint. For this project and assuming some potential risks of foundation movements should the underlying soils become elevated in moisture contents, the use of conventional type spread footings can be used, provided the design details as presented below are followed. Footing Foundations The upper level cohesive to slightly cohesive on-site subsoils are soft to medium stiff or loose to medium dense, with a slight tendency to consolidate under increased loads, and, as such, has a potential for settlement under the anticipated heavy wall and column loads. Significant post- construction settlement of the structure(s) would be expected for footing foundations designed at the maximum design loads supported directly on these fine granular subsoils at relatively shallow depths. To reduce the potential for post-construction settlement caused by consolidation of the on-site cohesive to slightly cohesive subsoils, we suggest extending the foundation systems to the coarse Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 9 granular soils below or bear the foundation system on engineered/controlled approved fill material, either “re-working” the on-site or imported granular structural fill material, which extends to the coarse granular soils below. Across the building footprints, the coarse granular, dense to very dense sand and gravel zone was encountered at depths of approximately 4 to 9-feet below existing site grades. Consideration could be given to over-excavating and replacing the upper soils with controlled and compacted imported structural fill material. The on-site stockpile materials appears to exhibit “pit-run” type characteristics and may be conducive for reuse; however additional laboratory analyses will be required. The over-excavation in the footing areas should extend laterally in all directions at least 6-inches from the edges of the footings for each 12-inches of over- excavation. The over-excavation depth at each footing should equal the footing width up to a minimum over-excavation depth of 4-feet below the bottom of footings. Fill soils used to develop foundation bearing could consist of approved structural fill materials which are free from organic matter and debris. Structural fill consisting of CDOT Class 5, 6 or 7 aggregate base course materials, either natural or recycled concrete and/or equivalent could be considered. The fill material should extend to and possibly into the native coarse granular subsoils. The fill and backfill soils should be placed in loose lifts not to exceed 9 inches thick and adjusted to a moisture content of +/- 2 % of optimum moisture content, and compacted to at least 95% (for backfill portions) and 98%, (beneath all foundations), of standard Proctor maximum dry density per ASTM Specification D-698 or, as appropriate, 70% of relative density. After placement of the fill materials, care should be taken to avoid excessive wetting or drying of those materials. Bearing materials which are loosened or disturbed by the construction activities or materials which become dry and desiccated or wet and softened should be removed and replaced or reworked in place prior to construction of the overlying improvements. The outlined steps for preparing bearing materials will significantly reduce but not eliminate the potential for settlement of the building with consolidation of the underlying materials. Overexcavation of a greater depth of material could be considered to further reduce the potential for post-construction settlement. Preloading or surcharge loading could also be used to reduce future settlement potential. Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 10 Conventional footing foundations could be supported directly on the structural fill backfill soils as outlined above or be extended to the native coarse granular subsoils. For design of footing foundations bearing on either the native coarse granular subsoils or on the structural fill compacted to at least 98% of standard Proctor maximum dry density, we recommend using a net allowable total load soil bearing pressure not to exceed 2,000 psf. The net bearing pressure refers to the pressure at foundation bearing level in excess of the minimum surrounding overburden pressure. Total load should include full dead and live loads. Exterior foundations and foundations in unheated areas should be located at least 30 inches below adjacent exterior grade to provide frost protection. We recommend formed continuous footings have a minimum width of 12 inches and isolated column foundations have a minimum width of 24 inches. Lateral Earth Pressures Coefficient values for backfill with anticipated types of soils for calculation of active, at rest and passive earth pressures are provided in the table below. Equivalent fluid pressure is equal to the coefficient times the appropriate soil unit weight. Those coefficient values are based on horizontal backfill with backfill soils consisting of essentially granular materials with a friction angle of a 35 degrees or low volume change cohesive soils. For the at-rest and active earth pressures, slopes down and away from the structure would result in reduced driving forces with slopes up and away from the structures resulting in greater forces on the walls. The passive resistance would be reduced with slopes away from the wall. The top 30-inches of soil on the passive resistance side of walls could be used as a surcharge load; however, should not be used as a part of the passive resistance value. Frictional resistance is equal to the tangent of the friction angle times the normal force. Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 11 Soil Type Low Plasticity Cohesive Medium Dense Granular Wet Unit Weight 115 135 Saturated Unit Weight 135 140 Friction Angle (∅) – (assumed) 25° 35° Active Pressure Coefficient 0.40 0.27 At-rest Pressure Coefficient 0.58 0.43 Passive Pressure Coefficient 2.46 3.70 Surcharge loads or point loads placed in the backfill can also create additional loads on below grade walls. Those situations should be designed on an individual basis. The outlined values do not include factors of safety nor allowances for hydrostatic loads and are based on assumed friction angles, which should be verified after potential material sources have been identified. Care should be taken to develop appropriate drainage systems behind below grade walls to eliminate potential for hydrostatic loads developing on the walls. Those systems would likely include perimeter drain systems extending to sump areas or free outfall where reverse flow cannot occur into the system. Where necessary, appropriate hydrostatic load values should be used for design. Floor Slabs Similar to the foundation portion for the proposed 2-story slab-on-grade live/work unit buildings, and assuming a conventional type slab-on-grade structures, we recommend over-excavating a minimum of 2-feet of the existing slightly soft/compressible subsoils beneath all slab-on-grade sections and replacing those soils with engineered/controlled fill material as previously described the “foundation” section of this report. The engineered fill material replacement concept will not fully eliminate the possibilities of slab movement; but movements should be reduced and tend to be more uniform. We estimate the long term movement of slab-on-grade floors with properly prepared subgrade subsoils as outlined above utilizing imported structural fill as replacement material would be on the order of approximately ½-inch. Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 12 Additional floor slab design and construction recommendations are as follows: • 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. • Interior trench backfill placed beneath slabs should be compacted in a similar manner as previously described for footing and floor slab fill. • In areas subjected to normal loading, a 4 to 6-inch layer of clean-graded gravel or aggregate base course should be placed beneath interior floor slabs. • Floor slabs should not be constructed on frozen subgrade. • Other design and construction considerations, as outlined in the ACI Design Manual, Section 302.1R are recommended. Pavement Subgrades/On-Site and Off-Site Pavement Design Sections We expect the on-site pavements will include areas designated for automobile traffic and areas for heavy truck traffic. Heavy truck areas assume an equivalent daily load axle (EDLA) rating of 15 and automobile areas an EDLA of 5. For the Hickory Street roadway improvements we understand per the City of Fort Collins on November 11, 2010, should be designed to accommodate a classification of industrial/commercial collector status and be designed using an 18-kip equivalent daily load application (EDLA) value of 100. The Hickory Street roadway improvement should be designed and constructed in general accordance with LCUASS Pavement Design Criteria. Proofrolling and 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 undercut or stabilized in-place to achieve the appropriate subgrade support. Based on the subsurface Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 13 conditions encountered at the site, and the laboratory test results, it is recommended the on-site private drives and parking areas and Hickory Street be designed using an R-value of 15. Subgrade stabilization should be considered to mitigate for swelling soils along Hickory Street roadway improvement alignment, (i.e., swell-index values in excess of 2.0% based on a 150 psf loading scheme). The stabilization should include incorporation of Class “C” fly ash to enhance the subgrade integrity. An alternate would be to over-excavate and/or “cut to grade” to accommodate a minimum of 12 to 18-inch layer of non-expansive granular soils to be placed and compacted beneath the pavement section. If the fly ash alternative stabilization approach is selected, EEC recommends incorporating 13% (by weight) Class C fly ash, into the upper 12-inches of subgrade. Hot Mix Asphalt (HMA) 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. 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 or consolidation of a wetted subgrade. Thus, the pavement may be adequate from a structural standpoint, yet still experience cracking and 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. The pavement sections could be constructed directly on the approved on-site subgrade soils. Those soils also have low remolded subgrade strength. The subgrades should be thoroughly evaluated and proofrolled prior to pavement construction. Recommended pavement sections are provided below in TABLE I for the on-site pavement areas and Table II for the proposed Hickory Street roadway improvements. The hot bituminous pavement (HBP) should be grading S (75) with PG 58-28 oil. The aggregate base should be Class 5 or Class 6 base. Portland cement concrete, if utilized should have a minimum 28-day compressive strength of 3500 psi and should be air entrained. Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 14 HBP pavements may show rutting and distress in truck loading and turning areas. Concrete pavements should be considered in those areas. TABLE I – RECOMMENDED MINIMUM PAVEMENT SECTIONS Automobile Parking Heavy Duty Areas EDLA Reliability Resilient Modulus – Based on R-Value of 15 PSI Loss 5 75% 4195 2.5 15 75% 4195 2.5 Design Structure Number 2.21 2.61 Composite: Alternative A Hot Bituminous Pavement Aggregate Base Design Structure Number 4" 6" (2.42) 4" 8" (2.64) Composite: Alternative B Hot Bituminous Pavement Aggregate Base (1) Fly Ash Treated Subgrade (0.05 credit) Design Structure Number 3-1/2" 4" 12" (2.58) 3-1/2" 5" 12" (2.69) Composite: Alternative C Hot Bituminous Pavement Aggregate Base (2) Select Subbase – 12 to 18-inches structural fill Design Structure Number 3" 4" 12" (2.60) 3” 4" 12" (2.60) PCC (Non-reinforced) 5" 7" (1) If fly ash is utilized for the on-site pavement areas for stabilization purposes, it is recommended that at least the upper 12-inches of the prepared subgrade be treated with Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 15 TABLE I1– Hickory Street Widening Improvements (Minimum Pavement Thicknesses) Flexible Pavement Evaluation Hickory Street Equivalent Daily Load Application (EDLA) Design Traffic (20 year ESAL) Resilient Modulus, psi based on an (R-value of 15) Reliability Serviceability Loss (Terminal Service=2.3) Design Structural Number 100 1,095,000 4195 85 2.2 3.71 Composite Section: Alternative A Hot Bituminous Pavement S-75, PG 64-28 Hot Bituminous Pavement S-75, PG 58-28 Aggregate Base (Class 5 or Class 6) Structural Number - SN 3” @ 0.44 = 1.32 3” @ 0.44 = 1.32 10” @ 0.11 = 1.10 3.74 Composite Section: Alternative B – Composite Section with Fly Ash Hot Bituminous Pavement S-75, PG 58-28 Aggregate Base (Class 5 or Class 6) (1) Fly Ash Treated Subgrade – (full-credit at 0.10) Structural Number - SN 4” @ 0.44 = 1.76 8” @ 0.11 = 0.88 12” @ 0.10 = 1.20 3.84 Composite Section: Alternative C – Composite Section with Fly Ash Hot Bituminous Pavement S-75, PG 58-28 Aggregate Base (Class 5 or Class 6) (1) Fly Ash Treated Subgrade – (half-credit at 0.05) Structural Number - SN 5” @ 0.44 = 2.20 9” @ 0.11 = 0.99 12” @ 0.05 = 0.60 3.79 1) If fly ash is utilized for the off-site pavement areas for stabilization purposes, it is recommended that at least the upper 12-inches of the prepared subgrade be treated with approximately 13% fly ash (by weight) of Class C fly ash. In general accordance with LCUASS a strength coefficient value of 0.10 could be used for the 12-inch treated zone of subgrade material provided the 7-day compressive strengths achieve 150 psi, otherwise strength coefficient value of 0.05 could be used as an overall pavement thickness reduction factor concept and the use of Alternative C would apply. The recommended pavement sections are minimums and periodic maintenance should be expected. Longitudinal and transverse joints should be provided as needed in concrete pavements for Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 16 expansion/contraction and isolation. The location and extent of joints should be based upon the final pavement geometry. Sawed joints should be cut within 24-hours of concrete placement. All joints should be sealed to prevent entry of foreign material and dowelled where necessary for load transfer. Since the cohesive soils on the site have some shrink/swell potential, pavements could crack in the future primarily because of the volume change of the soils when subjected to an increase in moisture content to the subgrade. The cracking, while not desirable, does not necessarily constitute structural failure of the pavement. Stabilization of the subgrades will reduce the potential for cracking of the pavements. The collection and diversion of surface drainage away from paved areas is critical to the satisfactory performance of the pavement. Drainage design should provide for the removal of water from paved areas in order to reduce the potential for wetting of the subgrade soils. 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: • The subgrade and the pavement surface should be adequately sloped to promote proper surface drainage. • 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 approved proof rolled subgrade soils with the use of base course materials. 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 Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 17 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 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, rutting, or excessive drying. 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 EEC be contacted for additional alternative methods of stabilization, or a change in the pavement section. Other Considerations Positive drainage should be developed away from the structure and pavement areas with a minimum slope of 1-inch per foot for the first 10-feet away from the improvements in landscape areas. Care should be taken in planning of landscaping adjacent to the building and parking and drive areas to avoid features which would pond water adjacent to the pavement, foundations or stemwalls. Placement of plants which require irrigation systems or could result in fluctuations of the moisture content of the subgrade material should be avoided adjacent to site improvements. Lawn watering systems should not be placed within 5 feet of the perimeter of the building and parking areas. Spray heads should be designed not to spray water on or immediately adjacent to the structure or site pavements. Roof drains should be designed to discharge at least 5 feet away from the structure and away from the pavement areas. Earth Engineering Consultants, Inc. EEC Project No. 1102069 November 11, 2010 Page 18 GENERAL COMMENTS The analysis and recommendations presented in this report are based upon the data obtained from the soil borings performed at the indicated locations and from any other information discussed in this report. This report does not reflect any variations, which may occur between borings or across the site. The nature and extent of such variations may not become evident until construction. If variations appear evident, it will be necessary to re-evaluate the recommendations of this report. It is recommended that the geotechnical engineer be retained to review the plans and specifications so comments can be made regarding the interpretation and implementation of our geotechnical recommendations in the design and specifications. It is further recommended that the geotechnical engineer be retained for testing and observations during earthwork and foundation construction phases to help determine that the design requirements are fulfilled. This report has been prepared for the exclusive use of MTA Planning & Architecture, for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranty, express or implied, is made. In the event that any 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 valid unless the changes are reviewed and the conclusions of this report are modified or verified in writing by the geotechnical engineer. DRILLING AND EXPLORATION DRILLING & SAMPLING SYMBOLS: SS: Split Spoon - 13/8" I.D., 2" O.D., unless otherwise noted PS: Piston Sample ST: Thin-Walled Tube - 2" O.D., unless otherwise noted WS: Wash Sample R: Ring Barrel Sampler - 2.42" I.D., 3" O.D. unless otherwise noted PA: Power Auger FT: Fish Tail Bit HA: Hand Auger RB: Rock Bit DB: Diamond Bit = 4", N, B BS: Bulk Sample AS: Auger Sample PM: Pressure Meter HS: Hollow Stem Auger WB: Wash Bore Standard "N" Penetration: Blows per foot of a 140 pound hammer falling 30 inches on a 2-inch O.D. split spoon, except where noted. WATER LEVEL MEASUREMENT SYMBOLS: WL : Water Level WS : While Sampling WCI: Wet Cave in WD : While Drilling DCI: Dry Cave in BCR: Before Casing Removal AB : After Boring ACR: After Casting Removal Water levels indicated on the boring logs are the levels measured in the borings at the time indicated. In pervious soils, the indicated levels may reflect the location of ground water. In low permeability soils, the accurate determination of ground water levels is not possible with only short term observations. DESCRIPTIVE SOIL CLASSIFICATION Soil Classification is based on the Unified Soil Classification system and the ASTM Designations D-2488. Coarse Grained Soils have move than 50% of their dry weight retained on a #200 sieve; they are described as: boulders, cobbles, gravel or sand. Fine Grained Soils have less than 50% of their dry weight retained on a #200 sieve; they are described as : clays, if they are plastic, and silts if they are slightly plastic or non-plastic. Major constituents may be added as modifiers and minor constituents may be added according to the relative proportions based on grain size. In addition to gradation, coarse grained soils are defined on the basis of their relative in-place density and fine grained soils on the basis of their consistency. Example: Lean clay with sand, trace gravel, stiff (CL); silty sand, trace gravel, medium dense (SM). CONSISTENCY OF FINE-GRAINED SOILS Unconfined Compressive Strength, Qu, psf Consistency < 500 Very Soft 500 - 1,000 Soft 1,001 - 2,000 Medium 2,001 - 4,000 Stiff 4,001 - 8,000 Very Stiff 8,001 - 16,000 Very Hard RELATIVE DENSITY OF COARSE-GRAINED SOILS: N-Blows/ft Relative Density 0-3 Very Loose 4-9 Loose 10-29 Medium Dense 30-49 Dense 50-80 Very Dense 80 + Extremely Dense PHYSICAL PROPERTIES OF BEDROCK DEGREE OF WEATHERING: Slight Slight decomposition of parent material on joints. May be color change. Moderate Some decomposition and color change throughout. High Rock highly decomposed, may be extremely broken. HARDNESS AND DEGREE OF CEMENTATION: HICKORY STREET FORT COLLINS, COLORADO EEC PROJECT NO. 1102069 NOVEMBER 2010 DATE: RIG TYPE: CME45 FOREMAN: DG AUGER TYPE: 4" CFA SPT HAMMER: MANUAL SOIL DESCRIPTION D N QU MC DD -200 TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % @ 500 PSF TOPSOIL & VEGETATION _ _ 1 SANDY LEAN CLAY (CL) AASHTO A-6 _ _ brown 2 soft to medium stiff _ _ CS 3 4 2000 22.1 98.7 32 12 57.3 <500 psf None _ _ 4 _ _ SILTY SAND & GRAVEL (SM-SW) CS 5 50/10" 2000 10.5 115.7 dense to very dense _ _ 6 _ _ 7 _ _ 8 _ _ 9 _ _ SS 10 50/13" -- 8.2 _ _ 11 _ _ 12 _ _ 13 _ _ 14 _ _ 15 -- -- 16.3 *Boring caved in - no drive sample @14.0' auger cuttings _ _ BOTTOM OF BORING DEPTH 10.5' 16 _ _ 17 _ _ 18 _ _ 19 _ _ 20 _ _ 21 _ _ 22 _ _ 23 _ _ 24 _ _ 25 _ _ Earth Engineering Consultants A-LIMITS SWELL DATE: RIG TYPE: CME45 FOREMAN: DG AUGER TYPE: 4" CFA SPT HAMMER: MANUAL SOIL DESCRIPTION D N QU MC DD -200 TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % @ 500 PSF SPARSE VEGETATION _ _ 1 SILTY, CLAYEY SAND (SC-SM) AASHTO A-2-4 _ _ brown 2 medium stiff _ _ CS 3 5 2000 21.0 103.1 _ _ 4 _ _ CS 5 7 1500 22.6 103.0 27 6 35.1 <500 psf None _ _ 6 _ _ SILTY SAND (SM) 7 medium dense _ _ 8 _ _ SILTY SAND with GRAVEL (SM-SW) 9 dense _ _ medium dense to dense SS 10 37 -- 7.3 _ _ *intermittent COBBLES with increased depths 11 _ _ 12 _ _ 13 _ _ *Boring caved in - no drive sample @ 14.0' 14 BOTTOM OF BORING DEPTH 14.0' _ _ 15 _ _ 16 _ _ 17 _ _ 18 _ _ 19 _ _ 20 _ _ 21 _ _ 22 _ _ 23 _ _ 24 _ _ 25 _ _ Earth Engineering Consultants A-LIMITS SWELL DATE: RIG TYPE: CME45 FOREMAN: DG AUGER TYPE: 4" CFA SPT HAMMER: MANUAL SOIL DESCRIPTION D N QU MC DD -200 TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % @ 500 PSF TOPSOIL & VEGETATION _ _ 1 SANDY LEAN CLAY (CL) AASHTO A-6 _ _ brown 2 stiff to very stiff _ _ % @ 150 PSF with calcareous deposits & traces of gravel CS 3 12 9000+ 8.0 103.2 34 19 58.9 1000 psf 4.1% _ _ 4 _ _ SS 5 7 9000+ 14.4 _ _ 6 _ _ 7 _ _ 8 _ _ 9 _ _ SILTY SAND with GRAVEL (SM-SW) CS 10 24 -- 20.5 107.8 medium dense _ _ 11 _ _ 12 _ _ * Intermittent COBBLES with increased depths 13 _ _ 14 _ _ SS 15 28 -- 16.2 _ _ BOTTOM OF BORING DEPTH 15.5' 16 _ _ 17 _ _ 18 _ _ 19 _ _ 20 _ _ 21 _ _ 22 _ _ 23 _ _ 24 _ _ 25 _ _ Earth Engineering Consultants A-LIMITS SWELL DATE: RIG TYPE: CME45 FOREMAN: DG AUGER TYPE: 4" CFA SPT HAMMER: MANUAL SOIL DESCRIPTION D N QU MC DD -200 TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % @ 500 PSF TOPSOIL & VEGETATION _ _ 1 SANDY LEAN CLAY (CL) AASHTO A-6 _ _ brown 2 stiff to very stiff _ _ % @ 150 PSF with traces of gravel CS 3 17 9000+ 7.9 110.7 30 16 53.0 1600 psf 2.8% _ _ 4 _ _ SILTY, CLAYEY SAND (SC-SM) AASHTO A-2-4 SS 5 6 4000 16.7 brown _ _ soft to medium stiff/medium dense 6 _ _ 7 _ _ 8 SILTY SAND with GRAVEL (SM-SW) _ _ medium dense to dense 9 _ _ SS 10 33 -- 5.6 _ _ BOTTOM OF BORING DEPTH 10.5' 11 _ _ 12 _ _ 13 _ _ 14 _ _ 15 _ _ 16 _ _ 17 _ _ 18 _ _ 19 _ _ 20 _ _ 21 _ _ 22 _ _ 23 _ _ 24 _ _ 25 _ _ Earth Engineering Consultants A-LIMITS SWELL SWELL / CONSOLIDATION TEST RESULTS Swell Pressure: <500 psf % Swell @ 500: None Beginning Moisture: 22.1% Dry Density: 99.9 psf Ending Moisture: 20.4% Material Description: Sample Location: Liquid Limit: 32 Plasticity Index: 12 Brown SANDY LEAN CLAY (CL) AASHTO A-6 Boring 1, Sample 1, Depth 2' % Passing #200: 57.3% 0.0 2.0 4.0 6.0 8.0 10.0 Movement Swell Project: Project #: Date: 1102069 November 2010 Hickory Street Fort Collins, Colorado -10.0 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 10.0 0.01 0.1 1 10 Percent Movement Load (TSF) Water Added Consolidation Swell SWELL / CONSOLIDATION TEST RESULTS % Swell @ 500: Beginning Moisture: 22.6% Dry Density: 104.8 psf Ending Moisture: 18.8% Swell Pressure: <500 psf None Sample Location: Boring 2, Sample 2, Depth 4' Liquid Limit: 27 Plasticity Index: 6 % Passing #200: 35.1% Material Description: Brown SILTY, CLAYEY SAND (SC-SM) AASHTO A-2-4 0.0 2.0 4.0 6.0 8.0 10.0 Movement Swell Project: Project #: Date: Hickory Street Fort Collins, Colorado 1102069 November 2010 -10.0 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 10.0 0.01 0.1 1 10 Percent Movement Load (TSF) Water Added Consolidation Swell SWELL / CONSOLIDATION TEST RESULTS % Swell @ 150: Beginning Moisture: 8.0% Dry Density: 106.6 psf Ending Moisture: 20.3% Swell Pressure: 1000 psf 4.1% Sample Location: Boring 3, Sample 1, Depth 2' Liquid Limit: 34 Plasticity Index: 19 % Passing #200: 58.9% Material Description: Brown SANDY LEAN CLAY (CL) AASHTO A-6 0.0 2.0 4.0 6.0 8.0 10.0 Movement Swell Project: Project #: Date: Hickory Street Fort Collins, Colorado 1102069 November 2010 -10.0 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 10.0 0.01 0.1 1 10 Percent Movement Load (TSF) Water Added Consolidation Swell SWELL / CONSOLIDATION TEST RESULTS % Swell @ 150: Beginning Moisture: 7.9% Dry Density: 113.6 psf Ending Moisture: 16.9% Swell Pressure: 1600 psf 2.8% Sample Location: Boring 4, Sample 1, Depth 2' Liquid Limit: 30 Plasticity Index: 16 % Passing #200: 53.0% Material Description: Brown SANDY LEAN CLAY (CL) AASHTO A-6 0.0 2.0 4.0 6.0 8.0 10.0 Movement Swell Project: Project #: Date: Hickory Street Fort Collins, Colorado 1102069 November 2010 -10.0 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 10.0 0.01 0.1 1 10 Percent Movement Load (TSF) Water Added Consolidation Swell PROJECT: Hickory Street - Widening Improvements PROJECT NO. 1102069 LOCATION: Fort Collins, Colorado DATE Nov-10 MATERIAL DESCRIPTION: Sandy Lean Clay (CL ) AASHTO A-6 SAMPLE LOCATION: LIQUID LIMIT: 35 PLASTICITY INDEX: 19 %PASSING #200: 60.8 R-VALUE LABORATORY TEST RESULTS TEST SPECIMEN NO. 1 23 COMPACTION PRESSURE (PSI) 200 250 300 DENSITY (PCF) 116.7 119.1 121.2 MOISTURE CONTENT (%) 14.9 13.0 13.5 EXPANSION PRESSURE (PSI) 0.00 0.00 0.00 HORIZONTAL PRESSURE @ 160 PSI 132 122 112 SAMPLE HEIGHT (INCHES) 2.62 2.59 2.58 EXUDATION PRESSURE (PSI) 176.7 388.1 708.7 UNCORRECTED R-VALUE 13.8 19.1 25.0 CORRECTED R-VALUE 14.4 19.8 25.8 R-VALUE @ 300 PSI EXUDATION PRESSURE = 18 RESILIENT MODULUS, PSI = 4,627 RESISTANCE R-VALUE & EXPANSION PRESSURE OF COMPACTED SOIL - ASTM D2844 Composite Subgrade Sample - Test Boring B-3 and B-4 @ 1 - 4-feet 100 0 10 20 30 40 50 60 70 80 90 100 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 R-Value Exudation Pressure, PSF SURFACE ELEV N/A 24 HOUR N/A FINISH DATE 10/20/2010 AFTER DRILLING N/A SHEET 1 OF 1 WATER DEPTH START DATE 10/20/2010 WHILE DRILLING None LOG OF BORING B-4 HICKORY STREET FORT COLLINS, COLORADO PROJECT NO: 1102069 OCTOBER 2010 SURFACE ELEV N/A 24 HOUR N/A FINISH DATE 10/20/2010 AFTER DRILLING N/A SHEET 1 OF 1 WATER DEPTH START DATE 10/20/2010 WHILE DRILLING 10.0' LOG OF BORING B-3 HICKORY STREET FORT COLLINS, COLORADO PROJECT NO: 1102069 OCTOBER 2010 SURFACE ELEV N/A 24 HOUR N/A FINISH DATE 10/20/2010 AFTER DRILLING N/A SHEET 1 OF 1 WATER DEPTH START DATE 10/20/2010 WHILE DRILLING 6.0' LOG OF BORING B-2 HICKORY STREET FORT COLLINS, COLORADO PROJECT NO: 1102069 OCTOBER 2010 SURFACE ELEV N/A 24 HOUR N/A FINISH DATE 10/20/2010 AFTER DRILLING N/A SHEET 1 OF 1 WATER DEPTH START DATE 10/20/2010 WHILE DRILLING 5.5' LOG OF BORING B-1 HICKORY STREET FORT COLLINS, COLORADO PROJECT NO: 1102069 OCTOBER 2010 Limestone and Dolomite: Hard Difficult to scratch with knife. Moderately Can be scratched easily with knife. Hard Cannot be scratched with fingernail. Soft Can be scratched with fingernail. Shale, Siltstone and Claystone: Hard Can be scratched easily with knife, cannot be scratched with fingernail. Moderately Can be scratched with fingernail. Hard Soft Can be easily dented but not molded with fingers. Sandstone and Conglomerate: Well Capable of scratching a knife blade. Cemented Cemented Can be scratched with knife. Poorly Can be broken apart easily with fingers. Cemented approximately 13% fly ash (by weight) of Class C fly ash. (2) If the select subbase alternative is chosen, we recommend a minimum of 12-inches of imported structural fill be moisture conditioned and compacted to at least 95% of the materials standard Proctor dry density. For the structural number coefficient benefit we are using a design value of 0.07.