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HomeMy WebLinkAboutHEWLETT PACKARD OFFICE EXPANSION - Filed GR-GEOTECHNICAL REPORT/SOILS REPORT -I I 1 I 1 GEOTECHNICAL ENGINEERING REPORT HEWLETT PACKARD FORT COLLINS SITE I PROPOSED BUILDINGS 9 AND 10 FORT COLLINS, COLORADO IPROJECT NO. 20955192 December 7, 1995 I 1 1 1 Prepared for: HEWLETT PACKARD REAL ESTATE 1 3000 HANOVER STREET PALO ALTO, CALIFORNIA 94304 ATTN: MR. JOHN HANKEY, PROJECT MANAGER 1 Prepared by: I Terracon Consultants Western, Inc. Empire Division I 301 North Howes Street Fort Collins, Colorado 80521 I 1 I 11ErrIcnn __ I I IDecember 7, 1995 I Hewlett Packard Real Estate 3000 Hanover Street Palo Alto, California 94304 IAttn: Mr. John Hankey, Project Manager Re: Geotechnical Engineering Report-Proposed Hewlett Packard Fort Collins I Buildings 9 and 10, Fort Collins, Colorado Project No. 20955192 Terracon Consultants Western, Inc., Empire Division has completed a geotechnical engineering Iexploration for the proposed Buildings 9 and 10 at the Hewlett Packard Fort Collins facility located on Harmony and Minor Roads in southeast Fort Collins, Colorado. This study was performed in general accordance with our proposal number D2095285.1 dated October 31, 1995. IThe 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 Ifoundations and other earth connected phases of this project are attached. Subsoils at the site in general consist of lean clays with sand underlain by sandy lean clays which in II turn are underlain by silty sand with gravel and cobbles and clayston a/siltstone bedrock. Based on the anticipated loads and subsurface conditions, it is recommended the structures be supported by drilled pier foundation systems. Due to low to moderately expansive characteristics of the upper subsoils, Ispecial attention should be given to design of slabs on grade. Further details are provided in this report. I 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. ISincerely, TERRACON CONSULTANTS WESTERN, INC. I Empire Division ssm Pre ared b f E ce.. otrir Reviewed by: r® 'n /` cf 4 eil od William J.Attwooll, P.Eo.o •a 15329 I ,,*a Senior ngineering Geol,,'. y Assistant Office ManagesIIi,d4 '.-. a ego Copies to: Addressee (2) ' 'p A-S! J> °°04,00 0!°,1®° RBD, Inc. (1) o®1a®i a , s I H+L Architecture (1) Bierbach Consulting Engineers (1) I1 Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 TABLE OF CONTENTS 1 Letter of Transmittal Page No. li INTRODUCTION 1 PROPOSED CONSTRUCTION 1 SITE EXPLORATION 2 Field Exploration 2 Laboratory Testing 3 SITE CONDITIONS 4 SUBSURFACE CONDITIONS 4 Geology 4 Soil and Bedrock Conditions 4 Field and Laboratory Test Results 5 1 Groundwater Conditions 6 1 CONCLUSIONS AND RECOMMENDATIONS 6 Geotechnical Considerations 6 Foundation Systems 7 Basement Construction 10 Lateral Earth Pressures 10 Seismic Considerations 11 Floor Slab Design and Construction 11 Pavement Design and Construction 12 2 1 I Geotechnical Engineering Exploration I Hewlett Packard Real Estate Project No. 20955192 Earthwork 17 Site Clearing and Subgrade Preparation: 17 I Excavation:17 Fill Materials: 18 Placement and Compaction: 19 I Shrinkage 20 Slopes: 20 Compliance 21 IExcavation and Trench Construction 21 Drainage 21 I Surface Drainage: 21 Subsurface Drainage 22 I Additional Design and Construction Considerations 22 Exterior Slab Design and Construction 22 Underground Utility Systems 23 ICorrosion Protection 23 GENERAL COMMENTS 23 IAPPENDIX A Site Plan and Boring Location Diagram Logs of Borings I APPENDIX B 1 Laboratory Test Results APPENDIX C General Notes I I I I 3 1 I I IGEOTECHNICAL ENGINEERING REPORT HEWLETT PACKARD FORT COLLINS SITE I PROPOSED BUILDINGS 9 AND 10 FORT COLLINS, COLORADO I Project No. 20955192 December 7, 1995 I INTRODUCTION This report contains the results of our geotechnical engineering exploration for the proposed Buildings 9 and 10 additions and associated parking and drives at the Hewlett Packard f facility located on Harmony and Minor Roads in southeast Fort Collins, Colorado. The site is located in the Southwest 1/4 of Section 33, Township 7 North, Range 68 West of the 6th IPrincipal Meridian. The purpose of these services is to provide information and geotechnical engineering Irecommendations relative to: subsurface soil and bedrock conditions I groundwater conditions foundation design and construction basement construction lateral earth pressures floor slab design and construction pavement design and construction earthwork I 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 Iconditions, structures and our understanding of the proposed project. I PROPOSED CONSTRUCTION IBased on information provided by H+L Architecture and Bierbach Consulting Engineers, the proposed structures will be two and three-story, slab-on-grade steel frame buildings I 1 Geotechnical Engineering Exploration I Hewlett Packard Real Estate Project No. 20955192 Iexhibiting heavy column loads of between 350 and 450 kips. One or both of the buildings may have full or partial basement construction. Associated parking and drive areas will be I constructed along the north and east sides of the proposed buildings. The additions will be located north of Buildings 2 and 6 and west of an existing parking area. IGround floor level is anticipated at or near the finished floor elevation of Building 6 at. Elevation 4919. This will require placement of approximately 1 to 2 feet of fill below the proposed buildings. ISITE EXPLORATION g The scope of the services performed for this project included site reconnaissance by a geotechnical engineer, a subsurface exploration program, laboratory testing and engineering analysis. IField Exploration A total of 34 test borings were drilled on October 10 and 13 through 17, 1995. The borings were drilled to depths of 10 to 56 feet at the locations shown cn the Site Plan, Figure 1. Twenty-eight borings were drilled within the area of the proposed building additions, and 6 I borings were drilled in proposed pavements and drive areas. All borings were advanced with a truck-mounted drilling rig, utilizing 4-inch diameter solid stem and 341 ID hollow stem i augers. The borings were located in the field by measuring from existing building corners and site I features. Elevations were taken at each boring location by measurements with an engineer's level from a temporary bench mark (TBM) shown on the Site Plan,. The accuracy of boring locations and elevations should only be assumed to the level implied by the Imethods used. Continuous lithologic logs of each boring were recorded by the geotechnical engineer 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 Isamples of subsurface materials were obtained from pavement borings. were obtained bydrivingthe split-spoonresistancemeasurementssppoon into the I 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. I2 I Geotechnical Engineering ExplorationIHewlettPackardRealEstate Project No. 20955192 1 Groundwater measurements were made in each boring at the time of site exploration, and 1 to 3 days after drilling. In addition, one water sample was obtained for laboratory chemical Ianalysis. I Laboratory Testing I All samples retrieved during the field exploration were returned to the laboratory for I 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. The field I 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. I Selected soil and bedrock samples were tested for the following engineering properties: I Water content Plasticity Index Dry density R-Value I Consolidation Water soluble sulfate content Compressive strength I Expansion Shear Strength I The significance and purpose of each laboratory test is described in Appendix C. Laboratory I 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 Iother accepted standards. One bore hole water sample was collected from Boring 24 and was transported under IStandard Terracon Consultants Western Chain-of-Custody procedures to Technology Laboratory, Inc. for chemical analysis. The hollow stem augers were cleaned prior to drilling Boring 24 where a bore hole sample was obtained to reduce the possibility of' cross- contamination. Volatile organics were analyzed in accordance with EPA Method 8260. The results of these tests are included in Appendix B. I 1 3 1 1 Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 SITE CONDITIONS The southern portion of the site is in an area adjacent to Buildings 2 and 6 which is landscaped with grass, trees and shrubs and is adjacent to a paved parking lot. A perimeter drive passes through the center portion of the site, with a cyclone fence located to the north 1 of the drive. The area north of the fence consists of a vacant tract which is fallow ground vegetated with mowed weeds. The entire area is relatively flat and has minor drainage to the north and east. An existing sewer line passes through the fallow area in the northern portion of the site. Other utilities parallel the existing fence located in the central portion of the site. 1 SUBSURFACE CONDITIONS Geology The site 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 Flains. 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. Bedrock is the Cretaceous Pierre Formation, which underlies the site at depths of 260,1 to 33 feet below the surface. The bedrock is overlain by alluvial sands and clays of Pleistocene and/or Recent Age. Mapping completed by the Colorado Geological Survey indicates the site in an area of Moderate Swell Potential". Potentially expansive materials mapped in this area include bedrock, weathered bedrock and colluvium (surficial units). Soil and Bedrock Conditions The following describes the characteristics of the primary soil strata in order of increasing depths: Existing Fill Material: A large portion of the area tested is overlain by a 1 to 111 foot layer of fill material. The fill consists of lean clay with sand and sandy lean clay with 1 4 1 Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 gravel. The clay is moist and medium to very stiff. Portions of the fill are overlain with a 6-inch layer of silty topsoil. Silty Topsoil: A 6-inch layer of siltytopsoil underlies the surface of Borings 1YP9 through 10, 19, 20, 21, 26, 30, 31 and 33. The topsoil has been penetrated by root growth and organic matter. Lean Clay with Sand: This stratum underlies the topsoil and fill in Borings 2, 4, 5, 7 through 10, 12, 14 through 16, 18, 19, 21, 23, and 26 and extends to depths of 1 to 4 feet below the surface. The lean clay with sand varies to a lean clay, is soft to hard in consistency and dry to moist. Sandy Lean Clay: This stratum underlies the topsoil, fill or upper clay stratum in all borings and extends to the depths explored and/or the granular stratum below. The sandy lean clay varies to include some gravel with depth, is dry to moist, and medium to hard in consistency. Silty Sand with Gravel and Cobbles: The granular stratum was encountered below the upper clays at depths of 19 to 27 feet below the surface in Borings 1, 3, 5, 7, 9, 11, 13, 15, 16, 19, 21, 23, 24, 26, and 28 and extends to the bedrock below. The silty sand with gravel contains cobbles at depths ranging in size up to 8 inches or more in diameter. One to 2 foot layers of densely cemented cobbles were encountered within the granular stratum in Borings 15, 16, 18, 21, 24, and 26 at depths of 27 to 28 feet. The sand is loose to very dense and wet in situ. iltstone-Cla stone Bedrock: The bedrock was encountered in Borings 1, 3 5, 7,S v9 9, 11, 13, 16, 18, 19, 21, 23, 24, 26, and 28 at depths of 261,2 to 33 feet below the surface or extends to greater depths. The upper 2 to 5 feet of the bedrock is highly weathered; however, the underlying interbedded siltstone and claystone are moderately hard to hard. Field and Laboratory Test Results Field and laboratory test results indicate the clay soils exhibit moderate bearing characteristics and low to moderate swell potential. The granular stratum exhibits low to 1 moderate bearing characteristics, and the bedrock exhibits high to very high bearing characteristics and high swell potential. 5 I Geotechnical Engineering Exploration I Hewlett Packard Real Estate Project No. 20955192 IGroundwater Conditions IGroundwater was encountered at approximate depths of 24 to 26 feet in Borings 1, 3, 5, 7, 9, 11, 13, 15, 16, 18, 19, 21, 23, 24, 26 and 28 at the time of field exploration. The I remaining borings were dry to the depths explored. When checked 1 to 3 days after drilling, groundwater was measured in each of the deep borings at approximate depths of 2111 to 26 feet below the surface. Borings that were initially dry remained when checked 1 to 7 days I 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. Based upon review of U.S. Geological Survey maps ('Hillier, et al, 1983), regional groundwater is expected to be encountered in unconsolidated alluvial deposits, at depths Iranging from 10 to 20 feet below the existing ground surface at the project site. 1 CONCLUSIONS AND RECOMMENDATIONS IGeotechnical Considerations I The site appears suitable for the proposed construction. Potentially expansive soils and bedrock will require particular attention in the design and construction. IThe following foundation systems were evaluated for use on the site: straight shaft piers and grade beams drilled into bedrock; I spread footings and/or grade beams bearing on undisturbed soils; and, spread footings and/or grade beams bearing on engineered fill. IDesign criteria for alternative foundation systems are subsequently outlined. Use of the alternative foundation systems outlined in this report should be determined prior to Iconstruction. Slab-on-grade construction is considered acceptable for use when subgrade soils consist of Ithe on-site clays, provided that design and construction recommendations are followed. It is 1Hillier, Donald E.; Schneider, Paul A., Jr.; and Hutchinson, E. Carter, 1983, Depth to Water Table (1979) in the Boulder-Fort Collins-Greeley Area, Front Range Urban Corridor, Colorado, United States Geological Survey, Map 1-855- I. I 6 I I I Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 1 recommended that slabs be underlain by a minimum of 2 feet of moisture-controlled on-site clays or imported granular material. IFoundation Systems Io Drilled Piers I In view of the concentrated loads and subsurface conditions encountered, a grade beam and drilled shaft foundation system is recommended to support the proposed structures. Straight shaft piers, drilled a minimum of 5 feet into firm or harder bedrock, with a minimum Ishaft lengths of 15 feet are recommended. For axial compression loads, piers extending up to 10 feet into the firm bedrock may be 1 designed for a maximum end-bearing pressure of 15,000 pounds per square foot (psf), and skin friction of 1,500 psf. For piers extended 10 feet or more into the firm to harder bedrock, I a maximum allowable bearing pressure of 20,000 pounds per square foot is recommended. Skin friction of 2,000 psf is recommended for that portion of the pier 10 feet or more in the firm or harder bedrock. IPiers should be considered to work in group action if the horizontal spacing is less than six pier diameters. A minimum practical horizontal spacing between piers of at least three Idiameters should be maintained, and adjacent piers should bear at about the same elevation. The capacity of individual piers must be reduced when considering the effects of group action. Capacity reduction is a function of pier spacing and the number of piers within Ia group. If group action analyses are necessary, capacity reduction factors can be provided for the analyses. IRequired pier penetration should be balanced against potential uplift forces due to expansion of the subsoils and bedrock on the site. For design purposes, the uplift force on Ieach pier can be determined on the basis of the following equation: Up =20xD 1 Where: Up upliftkips,the force in ki s, and ID = the pier diameter in feet Uplift forces on piers should be resisted by a combination of dead-load and skin friction from 1 pier penetration in the bearing strata. I7 1 I Geotechnical Engineering Exploration I Hewlett Packard Real Estate Project No. 20955192 IDrilled piers should be designed to resist all induced lateral forces. The ultimate passive resistance of the upper clay overburden materials above existing groundwater may be Icomputed using the equation Pp = 285Z + 600 psf. Below existing groundwater, the ultimate passive resistance of the overburden materials may be computed using the I equation Pp = 300Z psf. In both cases, Z is the depth below the top of the stratum. A factor of safety of 3 should be used in conjunction with the above equation. For design of piers, a coefficient of horizontal subgrade reaction k in pounds per cubic inch may be determined I using the equation of k = k/1.5b where b equals the width of the pier in feet. A value of 50 pounds per cubic inch may be utilized for k in the above equation for on-site clays. I When the lateral capacity of drilled piers is evaluated by the L-Pile (COM 624) computer program, we recommend that internally generated load-deformation (P-Y) curves be used. For the clayey soils, we recommend that the "stiff clay with no water" condition be used. The Ifollowing parameters may be used for the design of laterally loaded piers, using L-Pile (COM 624) computer program: IParameters Compacted Structural Fill Clayey Natural Soils Sand and Gravel Unit Weight of Soil (pcf) 130 115 125' I Cohesion(psf) 0 2,000 0 I Angle of Internal Friction, 35 0 35 0(degrees) Strain Corresponding to 0.015 Max. Principal Stress Difference Esc) INotes: 1) Use of 65 pcf below the Iwater table Drilling to design depth should be possible with conventional single flight power augers on I the majority of the site. However, specialized drilling equipment, such as a rock bit or core barrel and a large-sized caisson drilling rig may be required to penetrate the densely cemented cobbles. Groundwater conditions indicate that temporary steel casing will be Irequired to properly drill and clean piers prior to concrete placement. Groundwater should be removed from each pier hole prior to concrete placement. Pier concrete should be placed immediately after completion of drilling and cleaning. If pier concrete cannot be I 8 Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 1 placed in dry conditions or in 3 inches or less of water, a tremie should be used for concrete placement. Due to potential sloughing and raveling, foundation concrete quantities may exceed calculated geometric volumes. If casing is used for pier construction, it should be withdrawn in a slow continuous manner maintaining a sufficient head of concrete to prevent infiltration of water or the creation of voids in pier concrete. Pier concrete should have relatively high fluidity when placed in cased pier holes and/or through a tremie. Pier concrete with slump in the range of 5 to 7 inches is recommended. Free-fall concrete placement in piers will only be acceptable if provisions are taken to avoid striking the concrete on the sides of the hole or reinforcing steel. The use of a bottom-dump hopper, or an elephant's trunk discharging near the bottom of the hole where concrete segregation will be minimized, is recommended. To provide increased resistance to potential uplift forces, the sides of each pier should be mechanically roughened in the bearing strata below. This should be accomplished by a roughening tooth placed on the auger. Pier bearing surfaces must be cleaned prior to concrete placement. A representative of the geotechnical engineer should inspect the bearing surface and pier configuration. Conventional-Type Spread Footings Lightly loaded structures outside the main structural system may be supported on spread footing foundations bearing upon undisturbed soils and/or engineered fill. The footings may be designed for a maximum bearing pressure of 1,500 psf. In addition, due to the presence of low- to moderately swelling subsoils on the site, the footings should be sized to maintain a minimum dead-load pressure of 500 psf. The design bearing pressure applies to dead loads plus 1/2 of design live load conditions. The design bearing pressure may be increased by one-third when considering total loads that include wind or seismic conditions. Existing fill on the site should not be used for support of foundations without removal and recompaction. Any additional fill should be placed prior to foundation construction to allow for some consolidation of the subsoils from the added weight of the new fill. IExterior footings should be placed a minimum of 30 inches below finished grade for frost protection. Finished grade is the lowest adjacent grade for perimeter footings. Footings should be proportioned to minimize differential foundation movement. Proportioning on the basis of equal total settlement is recommended; however, proportioning to relative constant dead-load pressure will also reduce differential settlement between 9 1 Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 adjacent footings. Total settlement resulting from the assumed structural loads is estimated to be on the order of 3/4 inch. Proper drainage should be provided in the final design and during construction to reduce the settlement potential. 1 Basement Construction Groundwater was encountered on the site at depth of 21 to 36 feet below existing grade. Full-depth basement construction is considered feasible on the site provided that basement subgrade is 5 feet above existing groundwater. To reduce the potential for groundwater to enter the basement of the structure, installation of a dewatering system is recommended. The dewatering system should, at a minimum, include an underslab gravel drainage layer sloped to a perimeter drainage system. The drainage system should be constructed around the exterior perimeter of the basement foundation and should consist of a properly sized perforated pipe, embedded in free- draining gravel, placed in a trench at least 12 inches in width. The gravel should extend a minimum of 3-inches beneath the bottom of the pipe and at least 1 foot above the bottom of the foundation wall. The gravel should be covered with drainage fabric prior to placement of foundation backfill. The drainage system should slope at least .percent and should empty into a suitable outlet, such as a sump and pump system. The underslab drainage layer should consist of a minimum 8-inch thickness of free-draining gravel meeting the specifications of ASTM C33, Size No. 57 or 67. The drainage pipe should be perforated, rigid wall and a minimum 4-inch diameter. Cross- connecting drainage pipes should be provided beneath the slab at h-points and should I discharge to the perimeter drainage system. Lateral Earth Pressures For soils above any free water surface, recommended equivalent fluid pressures for unrestrained foundation elements are: Active: Cohesive soil backfill (clay) 45 psf/ft Cohesionless soil backfill (silty sand with gravel) 35 psf/ft 10 1 Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 1 Passive: Cohesive soil backfill (clay)...... .......... .. . 360 psf/ft Cohesionless soil backfill (silty sand with gravel)..............., 420 psf/ft Coefficient of base friction (gravel) 0.35 Adhesion at base of footing 500 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 with gravel) 50 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 should not be used as backfill against retaining walls. Compaction of each lift adjacent to walls should be accomplished with hand- operated tampers or other lightweight compactors. Overcompaction may cause excessive lateral earth pressures which could result in wall movement. 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). Floor Slab Design and Constructionig Low to moderate expansive soils or engineered fill will support the slabs on grade. Some differential movement of a slab-on-grade floor system is possible should the subgrade soils increase in moisture content. Such movements are considered within general tolerance for normal slab-on-grade construction. To reduce potential slab movements, we recommend that slabs on grade be underlain by a minimum of 2 feet of moisture-controlled soil. Based on proposed grades, it appears that the majority of the site will require fill. Where grades do not allow for 2 feet of fill below slabs, the subgrade should be overexcavated to the required depth to allow for 2 feet of moisture-controlled fill. 11 t Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 1 Additional floor slab design and construction recommendations are as follows: Positive separations, and/or isolation joints should be provided between slabs and all 1 foundations columns or utility lines to allow independent movement. Contraction joints should be provided in slabs to control the location and extent of cracking. Maximum joint spacing of 15 to 20 feet in each direction is recommended. Joints should be a minimum of 25% of slab thickness plus inch. Interior trench backfill placed beneath slabs should be compacted in accordance with irecommended specifications outlined below. In areas subjected to normal loading, a minimum 4-inch layer of clean-graded gravel should be placed beneath interior slabs. For heavy loading, reevaluation of slab and/or base course thickness may be required. A minimum 8-inch layer of free-draining gravel should be placed beneath basement floor slabs in conjunction with the underslab drainage system. If moisture sensitive floor coverings are used on interior slabs, consideration should be given to the use of barriers to minimize potential vapor rise through the slab. Floor slabs should not be constructed on frozen subgrade. Other design and construction considerations, as outlined in the ACI Design Manual, Section 302.1 R are recommended. For structural design of concrete slabs-on-grade, a modulus of subgrade reaction of 100 pounds per cubic inch (pci) may be used for floors supported on existing or engineered fill consisting of on-site soils. A modulus of 200 pci may be used for floors supported on imported granular fill meeting the specifications outlined below. Pavement Design and Construction Design 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, and 7 for driveways and truck loading areas. 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 12 1 1 1 Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 The AASHTO criteria suggests that these moisture conditions aremoistureconditions. S O gg 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 1 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 1 drainage coefficient of 1.0 when applying the AASHTO criteria for design. For flexible pavement design, a terminal serviceability index of 2.0 was utilized along with an inherent reliability of 70 and a design life of 20 years. Using the correlated design R- value of 5, 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 1 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 650 psi (working stress 488 psi) was used for pavement concrete. The rigid pavement thickness 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: 1 1 13 1 I Geotechnical Engineering Exploration Hewlett Packard Real Estate IProject No. 20955192 Traffic Area AlterE:i.aim.,; aii,':•i•Lf,tec,on.i.mendeit PiVeitientSeClioiittocknest,luriCiii0}MORIMO i native Asphalt Aggregate mSeleotm '1.1.ant,PiiiJted.: : Portland Total Concrete; Base Subbase Bituminous Cement Surface Course Base >` Concrete I Automobile A 3 7 10 Parking B 2 3-1/2 5=1/2 I C 5 5 Main Traffic A 3 10 13 Corridors IB 2 4-1/2 6-1/2 C 6 6 Each alternative should be investigated with respect to current material availability and economic conditions. Rigid concrete pavement, a minimum of 6 inches in thickness, is Irecommended at the location of dumpsters where trash trucks will park and load, driveways or parking areas supporting heavy trucks. I The pavement sections presented herein are based on design parameters selected by Terracon based on experience with similar projects and soils conditions. Design parameters I such as design life, terminal serviceability index, modulus of rupture of concrete and inherent reliability may vary with specific project. Variation of these parameters may change the thickness of the pavement sections presented. Terracon is prepared to discuss the details I of these parameters and their effects on pavement design and reevaluate pavement.design • as appropriate. 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 1 for base course. Aggregate base course and select subbase 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 I bituminous base and/or asphalt concrete should conform to approved mix designs stating the Marshall or Hveem properties, optimum asphalt content, job mix formula and 14 1 1 1 Geotechnical Engineering Exploration Hewlett Packard Real Estate 1 Project No. 20955192 I 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 I asphalt concrete. 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 Ibe placed in maximum 3-inch lifts and should be compacted to a minimum of 95% Hveem density (ASTM D1560). IWhere rigid pavements are used, the concrete should be obtained from an approved mix design with the following minimum properties: I Modulus of Rupture @ 28 days 650 psi minimum Strength Requirements ASTM C94 I Minimum Cement Content 6.5 sacks/cu. yd. Cement.Type Type I Portland 1 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 I Maximum Allowable Slump 4 inches 1 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 IColorado Department of Transportation should be followed. Longitudinal and transverse joints should be provided as needed in concrete pavements for I 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 doweled where I 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. 1 15 1 1 Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 Future performance of pavements constructed on the clay soils at this site will be dependent upon several factors, including: 1 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 by minimizing excess moisture which 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. 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. 1 16 1 Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 Earthwork 1 Site Clearingand Subgrade Preparation: 1. Strip and remove existing vegetation, debris, fill 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 or relocated 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. All materials derived from the demolition of existing structures, utilities and pavements should be removed from the site and not be allowed for use in any on-site fills. 5. The site should be initially graded to create a relatively level surface to receive 1 fill, and to provide for a relatively uniform thickness of fill beneath proposed building structures. t6. All exposed areas which will receive fill, floor slabs and/or pavement, once properly cleared, 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. 1 17 I 111 Geotechnical Engineering Exploration Hewlett Packard Real Estate 1 Project No. 20955192 I 2.Depending upon depth of excavation and seasonal conditions, groundwater may be encountered in deep excavations on the site. Pumping from sumps may be utilized to control water within these excavations. I3.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 Iand drying. Overexcavation of wet zones and replacement with granular materials may be necessary. Lightweight excavation equipment may be required to reduce Isubgrade pumping. Use of lime, fly ash, kiln dust, cement or geotextiles could also be considered as a stabilization technique. Laboratory evaluation is recommended to determine theIeffectofchemicalstabilizationonsubgradesoilspriortoconstruction. I Proof-rolling of the subgrade may be required to determine stability prior to paving. Fill Materials: I1.Clean on-site soils or approved imported materials may be used as fill material for the following: 1 general site grading exterior slab areas foundation areas pavement areas I interior floor slab areas foundation backfill 2.Select granular materials should be used as backfill behind retaining walls. 1 3.Frozen soils should not be used as fill or backfill. I 4.Imported soils (if required) should conform to the following or be approved by the Project Geotechnical Engineer: 1 Percent finer by weight Gradation ASTM C136) g° 100 3" 70-100 No. 4 Sieve 50-80 I No. 200 Sieve 50 (max) 18 1 Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 Liquid Limit 35 (max) Plasticity Index 15 (max) Minimum R-value 5 5. Aggregate base should conform to Colorado Department of Transportation Class 5 or 6 specifications. Placement and Compaction: II.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 Material (ASTM D698) Subgrade soils beneath fill and paved areas 95 On-site soils or approved imported fill: Beneath foundations 98 Beneath slabs 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. 1 19 1 Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 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. 7. The upper 2 feet of clay below slabs should be compacted with a moisture content range of optimum moisture to 3 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: Estimated Shrink(-) Swell (+) Material Based on ASTM D698 On-site soils: Clays 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) 3:1 1 20 1 Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 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. Excavation and Trench Construction Excavations into the on-site soils will encounter a variety of conditions. Excavations into the clays can be expected to stand on relatively steep temporary slopes during construction. However, caving soils and/or groundwater may also be encountered at depth. 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. Drainage Surface Drainage: 1.Positive drainage should be provided during construction and maintained throughout the life of the proposed facility. 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. drains or scuppers should discharge into3.Downspouts, roof pp splash blocks or9 extensions when the ground surface beneath such features is not protected by exterior slabs or paving. 11 21 I Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 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 Compacted subgrade or existing clay soils will expand with increasing moisture content; therefore, exterior concrete grade slabs may heave, resulting in cracking or vertical offsets. The potential for damage would be greatest where exterior slabs are constructed adjacent to the building or other structural elements. To reduce the potential for damage, we recommend: exterior slabs be supported on fill with no, or very low expansion potential strict moisture-density control during placement of subgrade fills placement of effective control joints on relatively close centers and isolation joints between slabs and other structural elements provision for adequate drainage in areas adjoining the slabs use of designs which allow vertical movement between the exterior slabs and adjoining structural elements In those locations where movement of exterior slabs cannot be tolerated or must be held to an absolute minimum, consideration should be given to: Constructing slabs with a stem or key-edge, a minimum of 6 inches in width and at least 12 inches below grade; 1 supporting keys or stems on drilled piers; or 22 I Geotechnical Engineering Exploration Hewlett Packard Real Estate Project No. 20955192 providing structural exterior slabs supported on foundations similar to the building. o 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 D42531beusedasbedding. Where utilities are excavated below groundwater, temporary dewatering will be required during excavation, pipe placement and backfilling 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. The pipe backfill should be compacted to a minimum of 95 percent of Standard Proctor Density ASTM D698.. e Corrosion Protection Results of soluble sulfate testing indicate that ASTM Type I-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. I 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 pier and/or footing 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 1 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. 23 I Geotechnical Engineering Exploration99p Hewlett Packard Real Estate IIProject No. 20955192 I 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 Inecessary to re-evaluate the recommendations of this report. Our professional services were performed using that degree of care and skill ordinarily I 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 Icontractor reviewing this report must draw his own conclusions regarding site conditions and specific construction techniques to be used on this project. 1 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, I either specifically or by implication, any environmental assessment of the site or identification of contaminated or hazardous materials or conditions. If the owner is concerned about the potential for such contamination, other studies should be undertaken. 1 1 I 1 1 1 1 1 1 24 1