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HomeMy WebLinkAboutJEFFERSON COMMONS PUD - Filed GR-GEOTECHNICAL REPORT/SOILS REPORT -GEOTECHNICAL ENGINEERING REPORT STUDENT HOUSING WEST ELI7ABETH STREET FORT COLLINS, COLORADO PROJECT NO.20965032 March 27, 1996 Prepared for. JPI DEVELOPMENT PARTNERS 600 EAST LAS COLINAS BOULEVARD IRVING, TEXAS 75039 ATTN: MR. PATRICK RHAMEY Prepared by. Terracon Consultants Western, Inc. Empire Division 301 North Howes Street Fort Collins, Colorado 80521 Irerracon 1 March 27, 1996 JPI Development Partners 600 East Las Colinas Boulevard Irving, Texas 75039 Irerracon CONSULTANTS WESTERN, INC. P.O. Box 503 ° 301 N. Howes Fort Collins, Colorado 80522 970) 484-0359 Fax: (970) 484-0454 Larry G. O'Dell, P.E. William J. Attwool, P.E. Neil R. Sherrod, C.P.G. Attn: Mr. Patrick Rhamey Re: Geotechnical Engineering Report Proposed Student Housing, West Elizabeth Street Fort Collins, Colorado Project No. 20965032 Terracon Consultants Western, Inc., Empire Division has completed a geotechnical engineering exploration for the proposed student housing project to be located between West Elizabeth Street on the south and Orchard Place on the north, west of South Taft Hill Road in Fort Collins, Colorado. This study was performed in general accordance with our proposal number D2596043 dated February 20,1996. The results of Our engineering study, including the boring location diagram, laboratory test results, test boring records, and the geotechnical recommendations needed to aid in the design and construction of foundations and other earth connected phases of this project are attached. The soils at the site consist of lean clays with sands, sandy lean clays and silty and/or clayey sands with gravels. The upper subsoils are underlain by siltstone/claystone bedrock at depths of 311 to 13;1 feet. Based on the structures proposed and the subsurface conditions encountered, it is our opinion the proposed post -tensioned slab -on -ground foundation construction is feasible. Further details are provided in this report.. We appreciate the opportunity to be of service to you on this phase. of your project If you have any questions concerning this report, or if we may be of further service to you, please do not hesitate to contact us. Sincerely, TERRACON CONSULTANTS WESTERN, INC. Empire Division Prepared by: F50rcSy j Review y \\``A PLO c L WS eil R. Sh od a i ' ... iam J. Attwooll, P.E -o ti _ Senior Engineering G 16612k Office Manager :'o °•ee G : P °• eeeeee C,\ Copies to: Addresse F9 dF P R. SHEAPo i,SSI IN Al ``` Gefroh Hatt Offices of The Terracon Companies, Inc. Geotechnical, Environmental and Materials Engineers Arizona Arkansas Colorado Idaho Illinois Iowa Kansas o Minnesota Missouri N Montana Nebraska Nevada Oklahoma Tennessee Texas Utah Wyoming QUALITY ENGINEERING SINCE 1965 Terracon TABLE OF CONTENTS IPage No. Letterof Transmittal.............................................................................................................ii INTRODUCTION.................................................................................................................1 PROPOSEDCONSTRUCTION..........................................................................................1 SITEEXPLORATION..........................................................................................................2 FieldExploration......................................................................................................2 LaboratoryTesting.................................................................................................. 3 SITECONDITIONS.............................................................................................................3 SUBSURFACE CONDITIONS............................................................................................ 4 Geology................................................................................................................... 4 Soil and Bedrock Conditions................................................................................... 4 Field and Laboratory Test Results........................................................................... 5 Groundwater Conditions.......................................................................................:.. 5 CONCLUSIONS AND RECOMMENDATIONS......................................................... :....... a..6 Geotechnical Considerations....................................................................................6 Post -Tensioned Slab Foundation Systems..............................................................6 BoxCulvert .............................................................................................................. 7 LateralEarth Pressures...........................................................................................7 Seismic Considerations........................................................................................... 8 Pavement Design and Construction........................................................................ 8 Tennis and Basketball Courts..................................................................................11 Earthwork..............................................................................................................13 Site Clearing and Subgrade Preparation.....................................................13 Excavation...................................................................................................14 FillMaterials.................................................................................................15 Placement and Compaction.........................................................................16 Shrinkage.....................................................................................................16 Slopes.......................................................................................................:..17 Compliance..................................................................................................17 Excavation and Trench Construction...........................................................18 Drainage...............................................................................................................:..18 SurfaceDrainage.........................................................................................18 SubsurfaceDrainage...................................................................................19 Additional Design and Construction Considerations....................19 Exterior Slab Design and Construction ........................................................ 19 Underground Utility Systems................................:.......................................19 Corrosion Protection.................................................................................... 20 Swimming Pool Design and Construction.........:..........:................................ 20 GENERALCOMMENTS..................................................................................................... 20 1 Geotechnical Engineering Exploration JPI Development Partners Project No. 20965032 TABLE OF CONTENTS (cont'd) APPENDIX A Site Plan and Boring Location Diagram Logs of Borings APPENDIX B Laboratory Test Results APPENDIX C General Notes K, Terracon GEOTECHNICAL ENGINEERING REPORT PROPOSED STUDENT HOUSING WEST ELIZABETH STREET FORT COLLINS, COLORADO Project No. 20965032 March 27, 1996 INTRODUCTION Terracon This report contains the results of our geotechnical engineering exploration for the proposed student housing complex to be located on West Elizabeth Street, Fort Collins, Colorado. The site is located in the Northeast 1/4 of Section 16, Township 7 North, Range 69 West of the 6th Principal Meridian. The purpose of these services is to provide information and geotechnical engineering recommendations relative to: subsurface soil and bedrock conditions groundwater conditions foundation design and construction lateral earth pressures C floor slab design and construction pavement design and construction earthwork drainage The conclusions and recommendations contained in this report are based upon the results of field and laboratory testing, engineering analyses, and experience with similar soil conditions, structures and our understanding of the proposed project. PROPOSED CONSTRUCTION Based on information provided JPI Development Partners and Gefroh Hattman Architects; the proposed apartments will be three-story, wood frame structures founded at grade on post -tensioned slab -on -ground foundations. In addition to the thirteen apartment structures, an information center, and pool will be constructed near the south end of the site. Parking and drive areas will be constructed throughout the project area. Tennis and basketball courts are planned in the northeast comer of the site. West Elizabeth Street will be improved adjacent to the south side of the property, and Orchard Place will be extended 1 Geotechnical Engineering Exploration Terracon JPI Development Partners Project No. 20965032 through the north edge of the site. Grading plans indicate cuts of approximately 1 to 2 feet and fills of up to 8 feet below the proposed structures are anticipated throughout the project area. The existing natural drainage located in the north half of the site is to be maintained through the project area. A box culvert will be constructed to carry a drive over the drainage channel. SITE EXPLORATION The scope of the services performed for this project included site reconnaissance by an engineering geologist, a subsurface exploration program, laboratory testing and engineering analysis. 1 Field Exploration A total of 38 test borings were drilled on March 7 and 8, 1996 to depths of 5 to 20 feet at the locations shown on the Site Plan, Figure 1. Twenty-eight borings were drilled within the footprint of the proposed apartment buildings, information center and pool and ten- borings were drilled in the area of proposed parking and street pavements. All borings were advanced with a truck -mounted drilling rig, utilizing 4-inch and 6-inch diameter hollow stem augers. The borings were located in the field by pacing from property lines and/or topographic 1 features. Elevations were interpolated from topography shown on the preliminary grading plan prepared by Bury & Pittman dated February 7, 1996. The accuracy of boring locations and elevations should only be assumed to the level implied by the methods used. Continuous 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 pushing thin -walled Shelby tubes, or by driving split -spoon samplers. Representative bulk samples of subsurface materials were obtained from select pavement borings. Penetration resistance measurements were obtained by driving the split -spoon into the subsurface materials with a 140-pound hammer falling 30 inches. The penetration resistance value is a useful index to the consistency, relative density or hardness of the materials encountered. Groundwater measurements were made in each boring at the time of site exploration, and one to seven days after drilling. 2 v Geotechnical Engineering Exploration JPI Development Partners Project No. 20965032 Laboratory Testing Terracon All samples retrieved during the field exploration were returned to the laboratory for observation by the project geotechnical engineer, and were classified in accordance with the Unified Soil Classification System described in Appendix C. Samples of bedrock were classified in accordance with the general notes for Bedrock Classification. At that time, the field descriptions were confirmed or modified as necessary and an applicable laboratory testing program was formulated to determine engineering properties of the subsurface materials. Boring logs were prepared and are presented in Appendix A. Selected soil and bedrock samples were tested for the following engineering properties: Water content Dry density Consolidation Compressive strength Expansion Grain size Plasticity Index R-Value Water soluble sulfate content The significance and purpose of each laboratory test is described in Appendix C. Laboratory test results are presented in Appendix B, and were used for the geotechnical engineering analyses, and the development of foundation and earthwork recommendations. All laboratory tests were performed in general accordance with the applicable ASTM, local or other accepted standards. SITE CONDITIONS The site consists of a tract of land surrounded by single-family residential housing and multifamily apartments. The area is bordered to the west by an existing residential subdivision, on the south by West Elizabeth Street, to the east by apartment buildings, to the north by a bike path and a mobile home park. A vacant house and several outbuildings are located at the south end of the property adjacent to West Elizabeth Street. The terrain is relatively flat and slopes from both the north and south to a small intermittent drainage located in the northern half of the site. The drainage flows to the southeast through the property. The majority of the site is vegetated with trees and native grasses. Corrals and sheds are located near the southwest edge of the site. Several north -south running fences are located in the western portion of the site, and the entire property is fenced. Geotechnical Engineering Exploration Terracon JPI Development Partners Project No. 20965032 SUBSURFACE CONDITIONS Geology The proposed area is located within the Colorado Piedmont section of the Great Plains physiographic province. The Colorado Piedmont, formed during Late Tertiary and Early Quaternary time (approximately 2,000,000 years ago), is a broad, erosional trench which separates the Southern Rocky Mountains from the High Plains. Structurally, the site lies along the western flank of the Denver Basin. During the Late Mesozoic and Early Cenozoic Periods (approximately 70,000,000 years ago), intense tectonic activity occurred, causing the uplifting of the Front Range and associated downwarping of the Denver Basin to the east. Relatively flat uplands and broad valleys characterize the present-day topography of the Colorado Piedmont in this region. The site is underlain by the Cretaceous Pierre Formation. The Pierre Formation in this area consists of interbedded siltstones and claystones. The bedrock underlies the site at depths of 3"1 to 131,1 feet. The bedrock is overlain by residual and alluvial clays, silty sands and gravels of Pleistocene and/or Recent Age. Mapping completed by the Colorado Geological Survey ( Hart, 1972), indicates the, site in an area of "Moderate Swell Potential." Potentially expansive materials mapped in this area include bedrock, weathered bedrock and coiluvium (surficial units). Soil and Bedrock Conditions The following describes the characteristics of the primary soil strata in order of increasing depths: v Silty Topsoil: The majority of the area tested is overlain by a 6-inch layer of silty topsoil. The topsoil has been penetrated by root growth and organic matter. Existing Pavement and Fill Material: Three and one-half (3,,1) inches of asphalt underlain by 4 inches of aggregate base course were encountered in Boring 35 drilled through the existing pavement at the site. The existing pavement is underlain by a layer of fill and extends to a depth of 2 feet. Fill was also encountered at the surface of Borings 24, 29, 30 and 36 and extends to depths of to 2 feet below the surface. The fill consists of sandy lean clay with gravel, is moist and medium to stiff 1 in consistency. 1 Hart, Stephen S., 1972, Potentially Swelling Soil and rock /n the Front Range Urban Corridor, Colorado, Colorado Geological Survey, Environmental Geology No. 7. 4 Geotechnical Engineering Exploration Terracon JPI Development Partners Project No. 20965032 1 s Lean Clay with Sand: This stratum underlies the topsoil and/or fill in Borings 1 through 6, 10, 11, 12, 16 through 28, 30, 31, 33, 34 and 36 through 38 and extends to depths of 1 to 4;1 feet below the surface. The brown lean clay with sand varies to a fat clay with sand, is moist and stiff to very stiff in consistency. Sandy Lean Clay: This stratum underlies the topsoil, fill and upper clay stratum in a;; but Borings 9 and 29 and extends to the silty sand and gravel and/or bedrock below. The red to tan sandy lean clay is dry to wet and medium stiff to stiff in consistency. I• Silty Sand with Gravel: This stratum was encountered in Borings 1, 9, 15, 21 through 27 and 29 at depths of ;i to 81-1 feet below the surface and extends to the bedrock below or the depth explored. The silty sand with gravel is moist to wet and medium dense to dense in relative density. Siltstone-Claystone Bedrock: The bedrock was encountered in Borings 1 through 28, 31 and 37 at depths of 31,1 to 131, feet below the surface and extends to greater depths. The upper 1;i to 61-1 feet of the bedrock is highly weathered and moderately hard. The underlying interbedded siltstone and claystone is hard. Field and Laboratory Test Results Field and laboratory test results indicate the clay soils at the site exhibit moderate bearing characteristics and low to moderate swell potential. The bedrock exhibits high bearing characteristics and moderate to high swell potential. Groundwater Conditions Groundwater was encountered in Borings 8 and 33 at approximate depths of 4 to 18 feet at the time of field exploration. The remaining borings were dry at the time of drilling. When checked between one and seven days after drilling, groundwater was measured in Borings 1 through 19, 21, 23, 24, 26, 28 and 33 at approximate depths of 1" to 19 feet below the surface. Borings 20, 22, 25, 27, 29 through 32, 34, 37 and 38 remained dry one to seven days after drilling. Borings 35 and 36 were filled in immediately, after drilling. These observations represent only current groundwater conditions, and may not be indicative of other times, or at other locations. Groundwater levels can be expected to fluctuate with varying seasonal and weather conditions. Zones of perched and/or trapped groundwater may also occur at times in the subsurface soils overlying bedrock, on top of the bedrock surface or within permeable fractures in the 5 r rGeotechnical Engineering Exploration Terracon JPI Development Partners Project No. 20965032 bedrock materials. The location and amount of perched water is dependent upon several factors, including hydrologic conditions, type of site development, irrigation demands on or adjacent to the site, fluctuations in water features, and seasonal and weather conditions. 1 Fluctuations in groundwater levels can best be determined by implementation of a groundwater monitoring plan. Such a plan would include installation of groundwater monitoring wells, and periodic measurement of groundwater levels over a sufficient period of time. The possibility of groundwater fluctuations should be considered when developing design and construction plans for the project. CONCLUSIONS AND RECOMMENDATIONS Geotechnical Considerations Post -tensioned slab -on -ground foundations were evaluated for use at the site. Design and construction recommendations for foundation systems and other earth connected phases of the project are outlined below. Post -Tensioned Slab Foundation Systems It is our understanding that post -tensioned slab -on -ground construction is proposed to support the proposed buildings at the site. Post -tensioned slabs, thickened or turn -down edges and/or interior beams should be designed and constructed in accordance with the requirements of the Post -Tensioning Institute and the American Concrete Institute. The post -tensioned slab should be designed using the following criteria. Maximum Allowable Bearing Pressure............:............................................. 2,000 psf Edge Moisture Variation Distance, em Center Lift Condition..............................................................................5.5 feet Edge Lift Condition.................................................................................2.5 feet Differential Soil Movement, ym Center Lift Condition........................................................................2.75 inches Edge Lift Condition ..........................::........ ............0.57 inches 2 Design and Construction of Post -Tensioned Slabs -on -Ground (1982), Post -Tensioning Institute, First Edition. 6 1 Geotechnical Engineering Exploration Terracon JPI Development Partners 1 Project No. 20965032 Slab-Subgrade friction coefficient, m on polyethylene sheeting............................................................................ 0.75 on cohesionless soils....................................................................... ...1.00 on cohesive soils.......................................................................................:.2.00 It should be noted that ym is the estimated vertical movement at the center of a uniformly loaded slab. This is a theoretical value that is used in the design of post -tensioned slabs -on - grade and does not represent the settlements or heave that would be expected from the 1 actual loading conditions. The differential movement estimate is the maximum expected differential movement between column or load -bearing wall lines and the center of the slab, due to the actual anticipated loading. iTotal or differential settlement resulting from the assumed structural loads are estimated to be on the order of 3/4 to 1-1/2 inches. Box Culv ert 1 It is recommended the proposed box culvert be founded on the original, undisturbed subsoil. The box culvert founded on the original, undisturbed soil should be designed for a maximum bearing capacity of 2,000 pounds per square foot (dead load plus maximum live load). The predicted settlement under the above maximum loading should be less than one inch, generally considered to be within acceptable tolerances. A cutoff wall should be provided below the upstream and downstream end of the box culvert to minimize erosion below the culvert. Lateral Earth Pressures For soils above any free water surface, recommended equivalent fluid pressures for t unrestrained foundation elements are: Active: Cohesive soil backfill (clay)......................................................... ..40 psf/ft Cohesionless soil backfill (silty sand) .................................................... 35 psf/ft Passive: Cohesive soil backfill (clay) ................... .......... 360 psf/ft Cohesionless soil backfill (silty sand) .................................................. 420 psf/ft Coefficient of base friction(silty sand........................:....0.40 7 Geotechnical Engineering Exploration Terracon JPI Development Partners IProject No. 20965032 Adhesion at base of footing............................................................................... 500 psf Where the design includes restrained elements, the following equivalent fluid pressures are recommended: At rest: Cohesive soil backfill (clay) ...............:.60 psf/ft Cohesionless soil backfill (silty sand) .................................................... 55 psf/ft The lateral earth pressures herein are not applicable for submerged soils. Additional recommendations may be necessary if such conditions are to be included in the design. 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. 1 Overcompaction may cause excessive lateral earth pressures which could result in wall movement. Seismic Considerations The project site is located in Seismic Risk Zone I of the Seismic Zone Map of the United States as indicated by the 1994 Uniform Building Code. Based upon the nature of the subsurface materials, a seismic site coefficient, "s" of 1.0 should be used for the design of structures for the proposed project (1994 Uniform Building Code, Table No. 16-J). Pavement Design and Construction iDesign of pavements for the project have been based on the procedures outlined in the 1986 Guideline for Design of Pavement Structures by the American Association of State Highway and Transportation Officials (AASHTO). Traffic criteria provided for pavement thickness designs include equivalent 18-kip single axle loads (ESAL's) of 3 for automobile parking, 5 for drive areas, 20 for Orchard Place and 125 for West Elizabeth Street. Based upon AASHTO criteria, Colorado is located within Climatic Region VI of the United States. This region is characterized as being dry, with hard ground freeze and spring thaw. The spring thaw condition typically results in saturated or near -saturated subgrade soil 8 Geotechnical Engineering Exploration Terracon JPI Development Partners Project No. 20965032 moisture conditions. The AASHTO criteria suggests that these moisture conditions are prevalent for approximately 12-1/2% of the annual moisture variation cycle. Local drainage characteristics of proposed pavement areas are considered to vary from fair to good depending upon location on the site. For purposes of this design analysis, fair drainage characteristics are considered to control .the design. These characteristics, coupled with the approximate duration of saturated subgrade conditions, results in a design drainage coefficient of 1.0 when applying the AASHTO criteria for design. 1 For flexible pavement design, terminal serviceability indices of 2.0 for parking and drive areas, 2.5 for Orchard Place and West Elizabeth Street were utilized along with an 'inherent reliability of 70% for interior parking, 80% for Orchard Place, and 90% for West Elizabeth Street, and a design life of 20 years. Using the correlated design R-values of 6 and 9, appropriate ESAL/day, environmental criteria and other factors, the structural numbers (SN) of the pavement sections were determined on the basis of the 1986 AASHTO design equation. In addition to the flexible pavement design analyses, a rigid pavement design analysis was completed, based upon AASHTO design procedures. Rigid pavement design is based on an evaluation of the Modulus of Subgrade Reaction of the soils (K-value), the Modulus of Rupture of the concrete, and other factors previously outlined. The design K-value of 100 for the subgrade soil was determined by correlation to the laboratory tests results. A modulus of rupture of 600 psi. (working stress 488 psi) was used for pavement concrete. The rigid pavement thicknesses for each traffic category were determined on the basis of the AASHTO design equation. Recommended alternatives for flexible and rigid pavements, summarized for each traffic area, are as follows: i7 Geotechnical Engineering Exploration JPI Development Partners Project No. 20965032 Terracon Traffic ACea A[tet :' Recommended Pavement Sect op Thy ckness (inches native Asphalt :': Aggregate Select Plafit-Mixed Portland Total Concrete Base Subbase—. ittithhdus..:..> Cement Syrface Course Base Concre#e Automobile A 3 6 9 Parking B 2 3 5 C 5 5 Drive Areas A 3 7 10 B 2 N 514 C 6 6 Orchard A 4 10 14 Place B 3 411 7' C 7 7 West A 6 9 15 Elizabeth B 3 6 9 C 8 8 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 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 and/or plant -mixed bituminous base course should be composed of a mixture of aggregate, filler and additives, if required, and approved bituminous material. The bituminous base and/or asphalt concrete should conform to approved mix designs stating the Hveem properties, optimum asphalt content, job mix formula and recommended mixing and placing temperatures. Aggregate used in plant -mixed bituminous base course and/or asphalt concrete should meet particular gradations. Material meeting Colorado Department of Transportation Grading C or CX specification is recommended for asphalt concrete. 10 Geotechnical Engineering Exploration Terracon JPI Development Partners Project No. 20965032 Aggregate meeting Colorado Department of Transportation Grading G or C specifications is recommended for plant -mixed bituminous base course. 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 minimum of 95% Hveem density (ASTM D1560) ASTM D1561). Where rigid pavements are used, the concrete should be obtained from an approved mix design with the following minimum properties: Modulus of Rupture @ 28 days..............................................600 psi minimum Strength Requirements.................................................... ........ASTM C94 Minimum Cement Content ...................................................... 6.5 sacks/cu. yd. Cement Type.............................................................................Type I Portland Entrained Air Content.............................................................................6 to 8% Concrete Aggregate....................................ASTM C33 and CDOT Section 703 Aggregate Size........................................................................1 inch maximum Maximum Water Content....................................................0.49 lb/lb of cement Maximum Allowable Slump...................................................................4 inches Concrete should be deposited by truck mixers or agitators and placed a maximum of 90 minutes from the time the water is added to the mix.. Other specifications outlined by the Colorado Department of Transportation should be followed. Longitudinal and transverse joints should be provided as needed in concrete pavements for expansion/contraction and isolation. The location and extent of joints should be based upon the final pavement geometry and should be placed (in feet) at roughly twice the slab thickness (in inches) on center in either direction. Sawed joints should be cut within. 24- hours of concrete placement, and should be a minimum of 25% of slab thickness plus 1/4 inch. All joints should be sealed to prevent entry of foreign material and dowelled where necessary for load transfer. Where dowels cannot be used at joints accessible to wheel loads, pavement thickness should be increased by 25 percent at the joints and tapered to regular thickness in 5 feet. Tennis and Basketball Courts Subgrade below tennis and basketball courts should be prepared in accordance with the recommendations set forth in this report. It is recommended the courts be paved with a 11 Geotechnical Engineering Exploration Terracon JPI Development Partners Project No. 20965032 minimum of 2 inches of asphaltic concrete or 5 inches of nonreinforced concrete underlain by 6 inches of aggregate base course. Good positive drainage should be provided on the court surfaces. Positive drainage should also be provided away from the courts on all sides. It is recommended that 10 percent for the first 10 feet away from the courts be provided.. Future performance of pavements constructed on the clay soils at this site will be dependent upon several factors, including: maintaining stable moisture content of the subgrade soils and providing for a planned program of preventative maintenance. Since the clay soils on the site have shrink/swell characteristics, pavements could crack in the future primarily because of expansion 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. The performance of all pavements can be enhanced b minimizing excess moisture which. p P Y 9 can reach the subgrade soils. The following recommendations should be considered at minimum: Site grading at a minimum 2% grade away from the pavements; Compaction of any utility trenches for landscaped areas to the same criteria as the pavement subgrade; Sealing all landscaped areas in or adjacent to pavements to minimize or prevent moisture migration to subgrade soils; Placing compacted backfill against the exterior side of curb and gutter, and, Placing curb, gutter and/or sidewalk directly on subgrade soils without the use of base course materials. Preventative maintenance should be planned and provided for an on -going pavement management program in order to enhance future pavement performance. Preventative maintenance activities are intended to slow the rate of pavement deterioration and to preserve the pavement investment. Preventative maintenance consists of both localized maintenance (e.g. crack sealing and patching) and global maintenance (e.g. surface sealing). Preventative maintenance is usually the first priority when implementing a planned pavement maintenance program and provides the highest return on investment for pavements. 12 Geotechnical Engineering Exploration Terracon JPI Development Partners Project No. 20965032 Recommended preventative maintenance policies for asphalt and jointed concrete pavements, based upon type and severity of distress, are provided in Appendix D. Prior to implementing any maintenance, additional engineering observation is recommended to determine the type and extent of preventative maintenance. Earthwork Site Clearing and Subgrade Preparation: 1. Strip and remove existing vegetation, debris, and other deleterious materials from proposed building and pavement areas. All exposed surfaces should be free of mounds and depressions which could prevent uniform compaction. 2. If unexpected fills or underground facilities are encountered during site clearing, such features should be removed and the excavation thoroughly cleaned prior to backfill placement and/or construction. All excavations should be observed by the geotechnical engineer prior to backfill placement. 3. Stripped materials consisting of vegetation and organic materials should be wasted from the site or used to revegetate exposed slopes after completion of grading operations. If it is necessary to dispose of organic materials on -site, they should be placed in non-structural areas and in fill sections not exceeding 5 feet in height. 4. Finished subgrade below building and paved areas should be placed a minimum of 3 feet above existing groundwater. 5. Sloping areas steeper than 31 (horizontal:vertical) should be benched to reduce the potential for slippage between existing slopes and fills. Benches should be level and wide enough to accommodate compaction and earth moving equipment. 6. Demolition of the existing buildings should include removal of any foundation system. 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 -site fills. 1 7. The site should be initially graded to create a relatively level surface to receive fill, and to provide for a relatively uniform thickness of fill beneath proposed building structures. 13 Geotechnical Engineering Exploration Terracon JPI Development Partners Project No. 20965032 8. All exposed areas which will receive fill, floor slabs and/or pavement, once properly cleared and benched where necessary, should be scarified to a minimum depth of 8 inches, conditioned to near optimum moisture content, and compacted. Excavation: 1. It is anticipated that excavations for the proposed construction can be accomplished with conventional earthmoving equipment. 2. If excavations need to penetrate into the bedrock, use of a large track - mounted backhoe or jack -hammering may be needed to advance the excavation. 3. Finished subgrade below building and paved areas should be placed a minimum of 3 feet above existing groundwater. 4. Depending upon depth of excavation and seasonal conditions, groundwater may be encountered in excavations on the site. Pumping from sumps may be utilized to control water within excavations. 5. On -site clay soils in proposed pavement areas may pump or become unstable or unworkable at high water contents. Workability may be improved by scarifying and drying. Overexcavation of wet zones and replacement with 1 granular materials may be necessary. Lightweight excavation equipment may be required to reduce subgrade pumping. Minimizing construction traffic on - site is recommended. Use of lime, fly ash, kiln dust, cement or geotextiles could also be considered as a stabilization technique. Laboratory evaluation is recommended to determine the effect of chemical stabilization on subgrade soils prior to construction. Proof -rolling of the subgrade may be required to determine stability prior to paving. 14 Geotechnical Engineering Exploration JPI Development Partners Project No. 20965032 Fill Materials: Terracon 1. Clean on -site soils or approved imported materials may be used as fill material for the following: general site grading • exterior slab areas foundation areas pavement areas interior floor slab areas • foundation backfill 2. On -site bedrock materials are not recommended for use beneath structural areas of the site, or as backfill. Should bedrock materials be used for general site grading, placement in fills at non-structural locations on the site is recommended. 3. Select granular materials should be used as backfill behind retaining walls. 4. Frozen soils should not be used as fill or backfill. 5. Imported soils (if required) should conform to the following or be approved by the Project Geotechnical Engineer. It should be noted that design of post - tensioned slab -on -ground foundations are based in part on soil type and plasticity. Therefore, it is important all imported material be approved by the geotechnical engineer prior to placement. Percent fines by weight Gradation (ASTM C136) 611 ..................................................................................................... 100 W................................................................................................70-100 No. 4 Sieve................................................................................... 50-80 No. 200 Sieve.......................................................................... 50 (max) Liquid Limit................................................................... 35 (max) Plasticity Index.............................................................15 (max) Minimum R-value...................................................................... 9 6. Aggregate base should conform to Colorado Department of Transportation Class 5 or 6 specifications. 15 Geotechnical Engineering Exploration Terracon JPI Development Partners Project No. 20965032 Placement and Compaction: 1. Place and compact fill in horizontal lifts, using equipment and procedures that will produce recommended moisture contents and densities throughout the lift. 2. No fill should be placed over frozen ground. 3. Materials should be compacted to the following: Minimum Percent Compaction Material (ASTM D698) Subgrade soils beneath fill areas..............................................................95 On -site soils or approved imported fill: Beneath foundations.......................................................................98 Beneathslabs..........................................................................:....95 Beneath pavements........................................................................95 Utilities............................................................................................95 Miscellaneous backfill...................:............................:....................90 4. If a well defined maximum density curve cannot be generated by impact compaction in the laboratory for any fill type, engineered fill should be compacted to a minimum of 80 percent relative density as determined by ASTM D4253 D4254. 5. Granular soils should be compacted within a moisture content range of 3 percent below to 3 percent above optimum unless modified by the project geotechnical engineer. 6. Clay soils placed around or beneath foundations should be compacted within a moisture content range of optimum to 2 percent above optimum. Clay soils placed beneath pavement should be compacted within a moisture content range of 2 percent below to 2 percent above optimum. Shrinkage For balancing grading plans, estimated shrink or swell of soils and bedrock when used as compacted fill following recommendations in this report are as follows: 16 Geotechnical Engineering Exploration Terracon JPI Development Partners Project No. 20965032 Estimated Shrink(-) Swell (+) Material Based on ASTM D698 On -site soils: Clays.................................................................................15 to -20% Siltysands........................................................................10 to -15% On -site bedrock materials: Claystone-siltstone............................................................15 to -20% Slopes: 1. For permanent slopes in compacted fill areas, recommended maximum slope angles of 2%:1 (horizontal to vertical) for on -site materials are recommended. If steeper slopes are required for site development, stability analyses should be completed to design the grading plan. 2. The face of all slopes should be compacted to the minimum specification for fill embankments. Alternately, fill slopes can be over -built and trimmed to compacted material 3. For permanent slopes in cut areas, the following maximum angles are recommended as follows: Maximum Slope Material Horizontal: Vertical Cohesive soils (clays and silts)..............................................................3:1 Cohesionless soils .................................................... ........................ 2%2:1 Bedrock.................................................................................................. 2:1 If steeper slopes are required for site development, stability analyses should be completed to design the grading plan. 1 . Compliance Performance of slabs -on -grade, foundations and pavement elements supported on compacted fills or prepared subgrade depend upon compliance with "Earthwork" recommendations. , To assess compliance, observation and testing should be performed under the direction of the geotechnical engineer. 17 Geotechnical Engineering Exploration Terracon JPI Development Partners Project No. 20965032 Excavation and Trench Construction Excavations into the on -site soils will encounter a variety of conditions. Excavations into the clays and bedrock can be expected to stand on relatively steep temporary slopes during construction. However, caving soils and/or groundwater may also be encountered. The individual contractor(s) should be made responsible for designing and constructing stable, 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 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. Drainage Surface Drainage: 1. Positive drainage should be provided during construction and maintained throughout the life of the proposed complex. 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. 2. 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 least 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. 18 1 Geotechnical Engineering Exploration JPI Development Partners Project No. 20965032 Terracon 3. 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. 4. Sprinkler systems should not be installed within 5 feet of foundation walls. Landscaped irrigation adjacent to the foundation system should be, minimized or eliminated. Subsurface Drainage Free -draining, granular soils containing less than five percent fines (by weight) passing a No. 200 sieve should be placed adjacent to walls which retain earth. A drainage system consisting of either weep holes or perforated drain lines (placed near the base of the wall) should be used to intercept and discharge water which would tend to saturate the backfill. Where used, drain lines should be embedded in a uniformly graded filter material and provided with adequate clean -outs for periodic maintenance. An impervious soil should be used in the upper layer of backfill to reduce the potential for water infiltration. Additional Design and Construction Considerations Exterior Slab Design and Construction Exterior slabs -on -grade, exterior architectural features, and utilities founded on, or in backfill may experience some movement due to the volume change of the backfill. Potential movement could be reduced by: minimizing moisture increases in the backfill controlling moisture -density during placement of backfill using designs which allow vertical movement between the exterior features and adjoining structural elements Y placing effective control joints on relatively close centers C allowing vertical movements in utility connections Underground 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. Where utilities are excavated below groundwater, temporary dewatering will be required during excavation, pipe placement and backfilling 19 Geotechnical Engineering Exploration Terracon JPI Development Partners Project No. 20965032 operations for proper construction. 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 existing bedrock. If bedrock is used, all plus 6- inch material should be removed from it prior to its use. The pipe backfill should be compacted to a minimum of 95 percent of Standard Proctor Density ASTM D698. 1 0 Corrosion Protection Results of soluble sulfate testing indicate that ASTM Type 1-II Portland cement is suitable for all concrete on or below grade. Foundation concrete should be designed in accordance with the provisions of the ACI Design Manual, Section 318, Chapter 4. Swimming Pool Design and Construction The swimming pool should be bedded in a layer of free -draining granular material to provide a solid base for construction. A clean material with a maximum 1-1/2-inch size and a minimum 3/8-inch size is recommended. A reinforced gunite pool is acceptable for the site provided that the groundwater is not penetrated during construction. If the excavation extends into the groundwater, a one piece fiberglass or similar pool should be installed. As a precaution, pressure relief valves should be placed in the deep end of any pool constructed to prevent flotation should groundwater rise when the pool is empty. GENERAL COMMENTS It is recommended that the Geotechnical Engineer be retained to provide a general review of final design plans and specifications in order to confirm that grading and foundation recommendations have been interpreted and implemented. In the event that any changes of the proposed project are planned, the conclusions and recommendations contained in this report should be reviewed and the report modified or supplemented as necessary. The Geotechnical Engineer should also be retained to provide services during excavation, grading, foundation and construction phases of the work. Observation of post -tensioned slab -on -ground excavations should be performed prior to placement of reinforcing and concrete to confirm that satisfactory bearing materials are present and is considered a necessary part of continuing geotechnical engineering services for the project. Construction testing, including field and laboratory evaluation of fill, backfill, pavement materials, concrete and steel should be performed to determine whether applicable project requirements have been met. It would be logical for Terracon Consultants Western, Inc. to provide these additional services for continuing from design through construction and to determine the consistency of field conditions with those data used in our analyses. 20 Geotechnical Engineering Exploration Terracon JPI Development Partners Project No. 20965032 The analyses and recommendations in this report are based in part upon data obtained from the field exploration. The nature and extent of variations beyond the location of test borings may not become evident until construction. If variations then appear evident, it may be necessary to re-evaluate the recommendations of this report Our professional services were performed using that degree of care and skill ordinarily exercised, under similar circumstances, by reputable geotechnical engineers practicing in this or similar localities. No warranty, express or implied, is made. We prepared the report as an aid in design of the proposed project. This report is not a bidding document. Any contractor reviewing this report must draw his own conclusions regarding site conditions and specific construction techniques to be used on this project. This report is for the exclusive purpose of providing geotechnical engineering and/or testing information and recommendations. The scope of services for this project does not include, either specifically or by implication, any environmental assessment of the site or1identificationofcontaminatedorhazardousmaterialsorconditions. If the owner is concerned about the potential for such contamination, other studies should be undertaken. 21