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HomeMy WebLinkAboutJFK SENIOR APARTMENTS - Filed GR-GEOTECHNICAL REPORT/SOILS REPORT -GEOTECHNICAL ENGINEERING REPORT JFK SENIOR APARTMENTS JFK AND TROUTMAN PARKWAYS FORT COLLINS, COLORADO TERRACON PROJECT NO.20985182 October 23, 1998 Prepared for. KAUFMAN AND BROAD MULTIHOUSING GROUP INC. 320 GOLDEN SHORE, SUITE 200 LONG BEACH, CALIFORNIA 90802-4217 ATTN: MR. MIKE MARINI, P.E. Prepared by: Terracon 301 North Howes Street Fort Collins, Colorado 80521 Irerracon October 23, 1998 Kaufman and Broad Multihousing Group Inc. 320 Golden Shore, Suite 200 Long Beach, California 90802-4217 Atth- Mr. Mike Marini, P.E. Re: Geotechnical Engineering Report JFK Senior Apartments JFK and Troutman Parkways Fort Collins, Colorado Terracon Project No, 20985182 limiliii HIM Ilerracan 301 N. Howes • P.O. Box 503 Fort Collins, Colorado 80521-0503 970)484-0359 Fax: (970) 484-0454 Terracon has completed a geotechnical engineering exploration for the proposed senior apartment complex to be located on JFK and Troutman Parkways in Fort Collins, Colorado. This study was performed in general accordance with our proposal number 02098220 dated September 29, 1998. 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 subsurface soils at the site consist of sandy lean clay with gravel fill and topsoil underlain by sandy lean clay and clayey sand. Bedrock was encountered at a depth of 19 feet or greater, and groundwater was encountered at approximate depths of 8 to 14 feet below the surface. The results of field exploration and laboratory testing completed for this study indicate that the soils at the site have low to moderate expansive potential. The soils at anticipated foundation bearing depth have moderate load bearing capability. Based on the subsurface conditions encountered and the type of construction, we recommend that the proposed structures be supported by conventional -type spread footing and/or grade beam foundation system. A feasible foundation alternate would be to support the structures by post -tensioned slab -on -ground foundations. If conventional slab -on - grade construction is utilized, differential movement of the floor slab on grade may occur should the expansive soils become elevated in moisture content. Use of structural floor Arizona a Arkansas M Colorado ® Idaho M Illinois ® Iowa M Kansas M Minnesota M Missouri ® Montana Nebraska M Nevada M New Mexico ® North Dakota ® Oklahoma ® Tennessee ® Texas M Utah M Wisconsin ® Wyoming Quality Engineering Since 19.65 Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Terracon Project No. 20985182 systems structurally supported independent of the subgrade soils is a positive means of eliminating potentially detrimental effects of floor movement. Other design and construction recommendations, based upon geotechnical conditions, are presented in the report. We appreciate being of service to you in the geotechnical engineering phase of this project, and are prepared to assist you during the construction phases as well. If you have any questions concerning this report or any of our testing, inspection, design and consulting services, please do not hesitate to contact us. Sincerely, TERRACON N N S1 i11il0iliililj ved y: 'p,00 RFol'''i,. i® 9Q ro v -O a is J. Attwooll, P.E.: c e 829 ManagerAL Copies to: Addressee (2) JR Engineering Ltd. - Mr. Dave Klockman (2) Geotechnical Engineering Report Terracon Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 I TABLE OF CONTENTS Page No. ILetter of Transmittal .............. ................................... :............................................................. i INTRODUCTION....................:.............................................................................................1 PROPOSEDCONSTRUCTION.............................................................................:..:.:.:.......1 SITEEXPLORATION....................................................................................................:......2 FieldExploration .............................................. ........................................................... :2 LaboratoryTesting...........................:....:................................................ - .:..............3 SITECONDITIONS ............................ :........................................................... :.::..................... 3 SUBSURFACECONDITIONS ................................................ ...................................... :....:..4 Geology............. :......................................................... ................................................ 4 Soil and Bedrock Conditions •. ••..4 Field and Laboratory Test Results.. ...........................5 Groundwater Conditions........................................................... ....., .............5 ENGINEERING ANALYSES AND RECOMMENDATIONS...................................................5 Geotechnical Considerations 5 Foundation Systems .:. ........ ........................... ........ ;.......: 6 Post -Tensioned Slab Foundation Systems (Expansive Case) ........ 7 Lateral Earth Pressures.........................:......................_.............................................8 RetainingWall Drainage...._ ....:........................................9 SeismicConsiderations ................................. :..:.................................................. 9 Floor Slab Design and Construction., .................................... 9 Pavement Design and Construction ..................... ............................ 11 Earthwork...................................:....................................,......................... 14 GeneralConsiderations ........... ...................................... .................................. 14 SitePreparation..............................................._.......................:.... 14 SubgradePreparation.............................................................. 15 FillMaterials and Placement .................................. ....;:..................................... 15 Shrinkage ......................... :......................................... 16 Excavation and Trench Construction ..........................._ 17 Additional Design and Construction Considerations...................................................17 Exterior Slab Design and Construction.:...........................;...............................17 Underground Utility Systems....................................,.:................................18 CorrosionProtection ................................................. .......................................: 18 Geotechnical Engineering Report Terracon LKaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 Surface Drainage .......................... ........ .19 Swimming Pool Design and Construction.....................................................19 L A GENERAL COMMENTS ....................... 20 Figure No. SITEPLAN.............................:....:....:....:....:....:..:.....................:...........................................1 APPENDIX A Logs of Borings APPENDIX B Laboratory Test Results APPENDIX C General Notes APPENDIX D Pavement Notes iv L I j_ Terracon GEOTECHNICAL ENGINEERING REPORT JFK SENIOR APARTMENTS JFK AND TROUTMAN PARKWAYS FORT COLLINS, COLORADO TERRACON PROJECT NO. 20985182 OCTOBER 23, 1998 INTRODUCTION This report contains the results of our geotechnical engineering exploration for the proposed apartment complex to be located at the southeast corner of JFK and Troutman Parkways, Fort Collins, Colorado. The site is located in the Southwest 1/4 of Section 36, 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 floor slab design and construction pavement design and construction earthwork drainage The 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 by Kaufman and Broad, five apartment buildings, a recreation building, pool and spa and parking and drive areas are proposed for the complex located at the southeast comer of Troutman and JFK Parkways. It is anticipated the buildings will be two- to three-story slab -on -grade structures. Final site grading plans were Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 not available at the time of preparation of this report, however, ground floor levels are anticipated at or slightly above existing grade. SITE EXPLORATION The scope of the services performed for this project included a site reconnaissance by an engineering geologist, a subsurface exploration program, laboratory testing and engineering analyses. Field Exploration A total of 11 test borings were drilled on October 14, 1998. The borings were drilled to approximate depths of 10 to 20 feet at the locations shown on the Site Plan, Figure 1. Nine borings were drilled within the footprints of the proposed buildings and pool to depths of 20 feet. Two borings were drilled in the area of the proposed parking to depths of 10 feet. The borings were advanced with a truck -mounted drilling rig, utilizing 4-inch diameter solid stem augers. The borings were located in the field by pacing from existing property lines and/or existing site features. Ground surface elevations at each boring location were obtained 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 methods used to determine each. 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 means of pushing thin -walled Shelby tubes, or by driving split -spoon samplers. Bulk samples of subsurface materials were obtained from borings in pavement areas. 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 in estimating the consistency, relative density or hardness of the materials encountered. Groundwater conditions were evaluated in each boring at the time of site exploration, and one day after drilling. 2 Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 Laboratory Testing 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. Laboratory tests were conducted on selected soil samples and are presented in Appendix B. The test results were used for the geotechnical engineering analyses, and the development of foundation and earthwork recommendations. All laboratory tests were performed in general accordance with the applicable ASTM, local or other accepted standards. Selected soil and bedrock samples were tested for the following engineering properties: Water Content Dry Density Consolidation Compressive Strength SITE CONDITIONS Expansion Plasticity Index Water Soluble Sulfate Content The site consists of a vacant tract of land that is currently vegetated with native grass and weeds. The property is relatively flat, slopes toward the east and has positive drainage in this direction. A soil stockpile approximately 5 feet high is located in the southern portion of the property. The site is bordered by Troutman Parkway to the north, JFK Parkway to the west, existing apartments to the east and vacant land to the south. 3 Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 SUBSURFACE CONDITIONS Geology I 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 Pierre7] Formation. Sandstone of the Pierre Formation was encountered in a portion of the site at a depth of 19 feet. It is estimated the bedrock underlies the remainder of the site at depths of 20 to 30 feet. The bedrock is overlain by alluvial sands and clays 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 colluvium (surficial units). Soil and Bedrock Conditions Two (2) to 4%z feet of fill material was encountered in portions of the site. The fill consists of sandy lean clay with gravel. It is not known whether the fill has been uniformly or properly compacted. A 6-inch layer of silty topsoil penetrated by root growth and organic matter underlies the remainder of the site. The topsoil and fill are underlain by sandy lean. clay and clayey sand which extends to the depths explored and/or the bedrock below. Sandstone bedrock was encountered in Boring 5 at a depth of 19 feet. The clays are medium to hard and moist to wet, and the sands are moist to wet and loose to medium dense. J'Hart, Stephen S., 1972, Potentially Swelling Soil and Rock in the Front Range Urban Corridor, Colorado, Colorado Geological Survey, Environmental Geology No. 7. 4 J Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 Field and Laboratory Test Results Field and laboratory test results indicate that the clay soils and clayey sands .exhibit to moderate swell potential and moderate bearing characteristics. Groundwater Conditions Groundwater was encountered in all but Borings 7, 10 and 11 at approximate depths of 9 to 20 feet at the time of field exploration. When checked one day after drilling, groundwater was measured in all borings at approximate depths of 8Y2 to 14 feet; These observations represent groundwater conditions at the time of the field exploration, 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 (2Hillier, et al, 1983), regional groundwater beneath the project area predominates in colluvial or windblown materials, or in fractured weathered consolidated sedimentary bedrock located at a depth near ground surface. Seasonal variations in groundwater conditions are expected since the aquifer materials may not be perennially saturated. Groundwater is generally encountered at depths ranging from 5 to 20 feet below ground surface; depth to seasonal groundwater is generally 10 feet or less. The possibility of groundwater fluctuations should be considered when developing design and construction plans for the project. 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. ENGINEERING ANALYSES AND RECOMMENDATIONS Geotechnical Considerations The site appears suitable for the proposed construction from a geotechnical engineering point of view. Existing fill, potentially expansive soils and the depth to groundwater will require particular attention in the design and construction. 2 Hillier, 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. 5 Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 The following foundation systems were evaluated for use on the site: spread footings and/or grade beams bearing on undisturbed soils; spread footings and/or grade beams bearing on engineered fill; post -tensioned slabs -on -ground bearing on undisturbed soils; and, post -tensioned slabs -on -ground bearing on engineered fill. Design criteria for alternative foundation systems is subsequently outlined.: Differential movement of floor slab -on -grade could result should expansive soils become elevated in moisture content. Differential slab movement on the order of one inch or more is possible. Use of structural floor systems, structurally supported independent of the subgrade soils, is a positive means of eliminating the potentially detrimental effects of floor movement. Foundation Systems Due to the presence of moderate -swelling soils on the site, spread footing foundations bearing upon undisturbed subsoils and/or engineered fill are recommended for support for the proposed structures. The footings may be designed for a maximum bearing pressure of 2,500 psf. In addition, the footings should be sized to maintain a minimum dead -load pressure of 750 psf. The design bearing pressure applies to dead loads plus 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. This may require removal of up to 4Y2 feet of existing material. Exterior footings should be placed a minimum of 30 inches below finished grade for frost protection and to provide confinement for the bearing. soils. Finished grade is the lowest adjacent grade for perimeter footings. Footings should be proportioned to reduce differential foundation movement. Proportioning on the basis of equal total movement is recommended; however, proportioning to relative constant dead -load pressure will also reduce differential movement between adjacent 6 i L Terracon Geotechnical Engineering Report Kaufman and Broad Multi housing Group, Inc. Terracon Project No. 20985182 footings. Total movement resulting from the assumed structural loads is estimated to be on the order of 3/4 inch or less. Differential movement should be on the order of 1/2 to 3/4 of the estimated total movement. Additional foundation movements could occur if water from any source infiltrates the foundation soils; therefore, proper drainage should be provided in the final design and during construction. Foundations and masonry walls should be reinforced as necessary to reduce the potential for distress caused by differential foundation movement. The use of joints at openings or other discontinuities in masonry walls is recommended. Foundation excavations should be observed by the geotechnical engineer. If the soil conditions encountered differ significantly from those presented in this report, supplemental recommendations will be required. Post -Tensioned Slab Foundation Systems (Expansive Case) Post -tensioned slab construction can be considered as an alternate foundation system for the project. Post -tensioned slabs should be designed using criteria outlined by the Post - Tensioning Institute based on the following: Maximum Allowable Bearing Pressure.................................1,500 psf Edge Moisture Variation Distance, em Center Lift Condition....................................................5.5 feet Edge Lift Condition .... .................................................. 2.5 feet Differential Soil Movement, ym 6 Center Lift Condition.......:.:...::..................................::2,.b inches Edge Lift Condition..................................................0.6 inches Slab-Subgrade friction coefficient, µ on polyethylene sheeting..................................................0.75 on cohesionless soils.......................................................1.00 oncohesive soils..............................................................2.00 3Design and Construction of Post -Tensioned Slabs -on -Ground, Post -Tensioning Institute, First Edition. 7 Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 Post -tensioned slabs, thickened or tum-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. Lateral Earth Pressures For soils above any free water surface, recommended equivalent fluid pressures for unrestrained foundation elements are: Active: Cohesive soil backfill (on -site clay and clayey sand) .............45 psf/ft Passive: Cohesive soil backfill (on -site clay and clayey sand) ...........300 psf/ft a Coefficient of base friction...........................................................0.35 0 Adhesion at base of footing ... :;........ :.... ........... :.....I.................... 500 psf Where the design includes restrained elements, the following equivalent fluid pressures are recommended: At rest: Cohesive soil backfill (on -site clay and clayey sand) .............60 psf/ft The lateral earth pressures herein do not include any factor of safety and are not applicable for submerged soils/hydrostatic loading. Additional recommendations may be necessary if submerged 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. E= Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 Retaining Wall Drainage To reduce hydrostatic loading on retaining walls, a subsurface drain system should be placed behind the wall. The drain system should consist of free -draining granular soils containing less than five percent fines (by weight) passing a No. 200 sieve placed adjacent to the wall. The free -draining granular material should be graded to prevent the intrusion of fines or encapsulated in a suitable filter fabric. 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. As an alternative, a prefabricated drainage structure, such as geocomposite, may be used as a substitute for the granular backfill adjacent to the wall. 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 1997 Uniform Building Code. Based upon the nature of the subsurface materials, a soil profile type S, should be used for the design of structures for the proposed project (1997 Uniform Building Code, Table No. 16-J). Floor Slab Design and Construction Differential movement of floor slab -on -grade could result should expansive soils become. elevated in moisture content. Differential slab movement on the order of one inch or more is t possible. Use of structural floor systems, structurally supported independent of the subgrade soils, is a positive means of eliminating the potentially detrimental effects of floor movement. If slab -on -grade is utilized, the subgrade soils should be prepared as outlined in the earthwork section of this report. A common practice to reduce potential slab heave involves overexcavation of the expansive soils and replacing these materials with moisture - conditioned on -site soil or non -expansive imported fill. This alternative will not eliminate the possibility of slab heave; but movements should be reduced and tend to be more uniform. We would recommend a minimum 3 foot overexcavation below conventional slabs on grade. 0 Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 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 compacted soils at the site. Additional floor slab design and construction recommendations are as follows: Positive separations and/or isolation joints should be provided between slabs and all foundations, columns or utility lines to allow independent movement. Control joints should be provided in slabs to control the location and extent of cracking. A minimum 2-inch void space should be constructed above, or below non - bearing partition walls placed on the floor slab. Special framing details should be provided at door jambs and frames within partition walls to avoid potential distortion. Partition walls should be isolated from suspended ceilings. Interior trench backfill placed beneath slabs should be compacted in accordance with recommended 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. 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. 10 Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 Pavement Design and Construction The required total thickness for the pavement structure is dependent primarily upon the foundation soil or subgrade and upon traffic conditions. Based on the soil conditions encountered at the site, the anticipated type and volume of traffic and using a group index of 5 as the criterion for pavement design, the following minimum pavement thicknesses are recommended: Recommended f'avernent Thicknesses (Inches) Traffic Area Alterhative Asphalt pggregafe Plant INl xed Portland concrete Base Bituminous Cement Surface Course` Base Concrete': Total Automobile A 3 4 7 Parking B 2 2'/2 4'/ C 5 5 Main Traffic A 3 7 10 Corridors B 2 3'/2 5'/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 recommended at the location of dumpsters where trash trucks park and load. 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 11 i i Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 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. 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 .............................................. ............................... 4 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 12 Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 inch. All joints should be sealed to prevent entry of foreign material and dowelled where necessary for load transfer. 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 by minimizing excess moisture which can reach the subgrade soils. The following recommendations should be considered at minimum: Site grading at a m.in.imu. m 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 through 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. 13 Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 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. Earthwork C General Considerations The following presents recommendations for site preparation, excavation, subgrade preparation and placement of engineered fills on the project. All earthwork on the project should be observed and evaluated by Terracon. The evaluation of earthwork should include observation and testing of engineered fill, subgrade preparation, foundation bearing soils, and other geotechnical conditions exposed during the construction of the project. Site Preparation Strip and remove existing fill, 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. 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. All exposed areas which will receive fill; once properly cleared and benched where necessary, should be scarified to a minimum depth of eight inches, conditioned to near optimum moisture content, and compacted. 14 a Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 It is anticipated that excavations for the proposed construction can be accomplished With conventional earthmoving equipment. 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. Based upon the subsurface conditions determined from the geotechnical exploration, subgrade soils exposed during construction are anticipated to be relatively stable. However, the stability of the subgrade may be affected by precipitation, repetitive construction traffic or other factors. If unstable conditions develop, workability may be improved by scarifying.and drying. Overexcavation of wet zones and replacement with granular materials may be necessary. Use of lime, fly ash, kiln dust, cement or geotextiles could also be considered as a stabilization technique. Laboratory evaluation is recommended to determine the effect of chemical stabilization on subgrade soils prior to construction. Lightweight excavation equipment may be required to reduce subgrade pumping. Subgrade Preparation Subgrade soils beneath interior and exterior slabs, and beneath pavements should be scarified, moisture conditioned and compacted to a minimum depth of ten inches. The moisture content and compaction of subgrade soils should be maintained until slab or pavement construction. Fill Materials and Placement Clean on -site soils or approved imported materials may be used as fill material. Imported soils (if required) should conform to the following: Gradation Percent fines by weight ASTM C136) 611 ........................................................................... ............................100 3"....................................................................................................70-100 No. 4 Sieve ............................ :.... .................................................... 50-100 15 Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 No. 200 Sieve..............................................................................65 (max) Liquid Limit ............................................. ..:................. ....... 35 (max) Plasticity Index......................................................... ..... :..15 (max) Engineered fill should be placed and compacted in horizontal lifts, using equipment and procedures that will produce recommended moisture contents and densities throughout the lift. Recommended compaction criteria for engineered fill materials are as follows: Material Minimum Percent ASTM. D6981 Scarified subgrade soils.........................................................................95 On -site and imported fill soils: Beneath foundations •.•.............••••••95 Beneath slabs ..... :.:..:....:....................................................... :....95 Beneath pavements y Miscellaneous backfill (non-structural areas)..::.....................................90 i On -site or imported clay soils should be compacted within a moisture content range of 2 percent below, to 2 percent above optimum. Imported granular soils should be compacted within a moisture range of 3 percent below to 3 percent above optimum unless modified by the project geotechnical engineer. r 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 and clayey sands ........................... ....... :.....:...... -15 to -20% 16 L i Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 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 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. 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 17 Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 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 reduced, consideration should be given to: Constructing slabs with a stem or key -edge, a minimum of 6 inches in width and at least 12 inches below grade; or providing structural exterior slabs supported on foundations similar to the building. 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 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. Corrosion Protection Results of soluble sulfate testing indicate that ASTM Type I Portland cement is suitable for all concrete on and below grade. However, if there is no, or minimal cost differential, use of ASTM Type II Portland cement is recommended for additional sulfate resistance of construction concrete. Foundation concrete should be designed in accordance with the provisions of the ACI Design Manual, Section 318, Chapter 4. 18 Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 Surface Drainage Positive drainage should be provided during construction and maintained throughout the life of the proposed project. Infiltration of water into ufility or foundation excavations must be prevented during construction. Planters and other surface features which could retain water in areas adjacent to the building or pavements should be sealed or eliminated. In areas where sidewalks or paving do not immediately adjoin the structure, we recommend that protective slopes be provided with a minimum grade of approximately 5 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. Downspouts, roof drains or scuppers should discharge into splash blocks or extensions when the ground surface beneath such features is not protected by exterior slabs or paving. Sprinkler systems should not be installed within 5 feet of foundation walls. Landscaped irrigation adjacent to the foundation system should be minimized or eliminated. Swimming Pool Design and Construction As currently planned, the proposed project will include construction of a- swimming pool. The construction and performance of the pool may be highly affected by the presence of groundwater encountered at 8% feet. Excavation of the pool area by conventional rubber=tired equipment may encounter soft soils and/or severe pumping when nearing groundwater level. It may be necessary to excavate the deep portion of the pool with a backhoe or power shovel. To reduce impact of groundwater and/or soft soils, pool construction below a depth of 6 feet below existing grade is not recommended. Consideration should be given to the use of reinforced gunite concrete for pool construction. This material can normally withstand relatively large soil movements without cracking. However, because the bottom of the full -depth pool will extend into expansive clays, care'should be taken during construction to waterproof the pool so that leakage will not occur. 19 Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 A drainage system should be provided beneath the pool. The drain should consist of a minimum six inch layer of clean gravel (minimum 3/4-inch size) beneath the pool. The gravel layer beneath the pool should be sloped so that it will drain into perforated drain pipe. The layout of the perforated pipe should include at least one pipe running down the center of the pool lengthwise. The center pipe should be sloped to a sump located in the equipment room, permitting pump discharge. Pressure relieve valves should be provided in the base of the pool to prevent excessive uplift pressures from developing in the event of failure of the drain system. The soils that will support pool deck slabs around the pool could expand with increasing moisture content. To reduce possible damage that could be caused by expansive soils, we recommend: deck 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 deck slabs and adjoining structural elements Fill, backfill, and surface drainage in the pool area should be placed in accordance with the recommendations in the "Earthwork" section of this report: Grading should be provided for diversion of deck surface runoff away from the pool area. In no case should water be allowed to pond around the slab perimeter. GENERAL COMMENTS Terracon should be retained to review the final design plans and specifications so comments can be made regarding interpretation and implementation of our geotechnical recommendations in the design and specifications. Terracon also should be retained to provide testing and observation during excavation, grading, foundation and construction phases of the project. The .analysis and recommendations presented in this report are based upon the data obtained from the borings performed at the indicated locations and from other information 20 Terracon Geotechnical Engineering Report Kaufman and Broad Multihousing Group, Inc. Terracon Project No. 20985182 discussed in this report. This report does not reflect variations which may occur between borings or across the site. The nature and extent of such variations may not become evident until construction. If variations appear, it will be necessary to reevaluate the recommendations of this report. The scope of services for this project does not include 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. This report has been prepared for the exclusive use of our client for specific application to the project discussed and has., been prepared in accordance with generally accepted geotechnical engineering practices. No warranties, either express or implied, are intended or made. In the event that changes in the nature, design, or location of the project as outlined in this report, are planned, the conclusions and recommendations contained in this report shall not be considered valid unless Terracon reviews the changes, and either verifies or modifies the conclusions of this report in writing. 21 0. r 2 I c5 I z z N cs 2 I zm m I 2 I i I o 2 2 W Vjqjflogjl 1 1 9 N c U O W O u m 1 W e—I F LO 1nn Wz BOO 6ONO z E W o E— 0Om Z a 0 z p'ZOO D coE-0 04Qr,' w EA