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10-1282 (CSCS) Geotechnical Investigationr r GEOTECHNICAL INVESTIGATION PROPOSED CHEVROLET / CADILLAC DEALERSHIP 79225 HIGHWAY 111 LA QUINTA, CALIFORNIA -Prepared By- Sladden Engineering 45090 Golf Center Parkway, Suite F Indio, California .92201 (760) 772-3893 Sladden Englneedng /' ':1. q (ft'Sladden Engineering 45090 Golf Center Parkway, Suite F, Indio, CA 92201 (760) 863-0713 Fax (760) 863-0847 6782 Stanton Avenue, Suite A, Buena Park, CA 90621 (714) 523-0952 Fax (714) 523-1.369 450 Egan Avenue, Beaumont, CA 92223 (951) Sas-7743 Fax (957) 84$.8863 800 E. Florida Avenue, Hemet, CA 92543 (951) 766-8777 Fax (951) 766-8778 August 20, 2010 Project No. 544-10113 10-08-190 Ken Garff Automotive Group 459 South Main Street, Suite 1190 Salt Lake City, Utah 84115 Subject: Geotechnical investigation Project: Proposed Chevrolet/Cadillac Dealership 79225 Highway 111 La Quinta, California Sladden Engineering is pleased to present the results of our geotechnical investigation for the proposed Chevrolet/Cadillac dealership renovation and additions to be constructed at 79225 Highway 111 in the City of La Quinta, California. Our services were completed in accordance with our proposal for geotechnical engineering services dates! July 12, 2010 and your authorisation to proceed with the work. The purpose of. our investigation was to explore the subsurface conditions at the site in order to provide recommendations for foundation design and site preparation. Evaluation of environmental issues and hazardous wastes was not included within the scope of services provided. The opinions, recommendations and design criteria presented in this report are based on our field exploration program, laboratory testing and engineering analyses. Based on the results of our investigation, it is our professional opinion that the proposed project is feasible provided the recommendations presented in this report are implemented in the design and carried out through construction. We appreciate the opportunity to provide service to you on this project. If you have any questions regarding this report, please contact the undersigned. Respectfully submitted, SLADDEN ENGINEERING Matthew). Cohn Brett L. Anderson Project Geologist Principal Engineer SER/mc Copies: 6/Addressee Sladden Engineering GEOTECHNICAL INVESTIGATION PROPOSED CHEVROLET/CADILLAC DEALERSHIP 79225 HIGHWAY 111 LA QUINTA, CALIFORNIA August 20, 2010 TABLE OF CONTENTS INTRODUCTION................................................................................................................................... 1 PROJECTDESCRIPTION..:.............................................................................................................I...... 1 SCOPEOF SERVICES............................................................................................................................. 2 SITECONDITIONS............................................................................................................................ 2 GEOLOGICSETTING ...................................,...,.......,........,................................... 3 SUBSURFACECONDITIONS................................................................................................................3 SEISMICITYAND FAULTING....................................:.........................................................................4 CBCDESIGN PARAMETERS.................................................................................................................5 GEOLOGICHAZARDS...........................................................................................................................5 CONCLUSIONS...................................................................................................................................... 7 EARTHWORK AND GRADING......................................................................... 8 f Stripping....................................................................................................................... ....... 8 ..,.. ..... .. Preparationof Building Areas........................................................................................................ 8 Compaction....................................................................................................................................... 8 Shrinkage and Subsidence.............................................................................................................. 9 FOUNDATIONS SPREAD FOOTINGS ... ..................................................................................... 9 SLABS -ON -GRADE ................. . ......................... . ......,.,....................10 PRELIMINARY PAVEMENT DESIGN................................................................................................10 SOLUBLESULFATES.............................................................................................................................11 UTILITYTRENCH BACKFILL ..........................................:...................................................................11 EXTERIOR CONCRETE FLATWORK.................................................................................................11 DRAINAGE.......................................................................:......................................................................11 LIMITATIONS........:................:...............................................................................................................12 ADDI'i'fONAL SERVICES ................................................. _................................................................... 12 REFERENCES..........................................................................................................................................13 FIGURES - Site Location Map Regional Geologic Map Borehole Location Plan APPENDIX A - Field Exploration APPENDIX B- Laboratory Testing , ' S/adden Engineering August 20, 2010 -1- .. Project No. 544-10113 10-08-190 INTRODUCTION This report presents the results of the geotechnical investigation performed by Sladden Engineering (Sladden) for the Chevrolet/Cadillac dealership located at 79225 Highway 1.11 in the City of La Quinta, California. The site is located on the SW '/4 of Section 29, Township 5 South, Range 7 East (SBBM) at approximately 33.70681 degrees north latitude and 116.28260 degrees west longitude. The approximate location of the site is indicated on the Site Location Map (Figure 1). Our investigation was conducted in order to evaluate the engineering properties of the subsurface materials, to evaluate their in-situ characteristics, and to provide engineering recommendations and design criteria for site preparation, foundation design and the design of various site improvements. This study also includes a review of published and unpublished geotechnical and geological literature regarding seismicity at and near the subject site. PROJECT DESCRIPTION Based on the provided Site Plan, and our preliminary conversations, it is our understanding that the proposed project will consist of constructing a new showroom, service bay expansion (addition) and showroom expansion (addition). Sladden anticipates that the proposed project will also include new concrete flatwork and various associated site improyements. For our analyses we expect that the new construction will consist of relatively lightweight wood -frame structures supported on conventional Grading plans and finished floor elevations were not available prior to the preparation of this report. However, based on the relatively level nature of the site and the anticipated scope of work, Sladden expects that grading will be limited to minor cuts and fills in order to accomplish the desired pad elevations and provide adequate gradients for site drainage. This does not include the removal and recompaction of foundation bearing soil within the building envelope. Upon completion of precise grading plans, Sladden should be retained in order to ensure that the recommendations presented within in this report are incorporated into the design of the proposed project. Structural foundation loads were not available at the time of this report. Based on our experience with relatively lightweight strictures,, we expect that isolated column loads will be less than 40 kips and continuous wall loads will •be less th4n 3.0 kips per linear foot. If these assumed loads vary significantly from the actual loads, we should be consulted=to verify the applicability of the recommendations provided. Sladden Engineering I August 20, 2010 .2. Project No. 544-101.13 10-08-190 SCOPE OF SERVICES The purpose of our investigation was to determine specific engineering characteristics of the surface and near surface soil in order to develop foundation design criteria and recommendations for site preparation. Exploration of the site was achieved by drilling four (4) exploratory boreholes to a maximum depth of approximately 51.5 feet below the existing ground surface (bgs). Specifically, our site characterisation consisted of the following tasks: • Site reconnaissance to assess the existing surface conditions on and adjacent to the site. • Advancing'four (4) exploratory boreholes to depths of up to 51.5 feet bgs in order to characterize the subsurface soil conditions. Representative samples of the soil were classified in the field and retained for laboratory testing and engineering analyses, • Performing laboratory testing on selected samples to evaluate their engineering characteristics. • Reviewing geologic literature and discussing geologic hazards. • Performing engineering analyses to develop recommendations for foundation design and site preparation. • The preparation of this report summarizing our work at the site. SITE CONDITIONS The site is located on the northwest comer of La Quinta Drive and Auto Center Drive in the City of La Quinta, California. The site consists of approximately 3.58 acres and is formally identified by the County of Riverside as APN 600-020-014. The site is occupied by an existing automobile dealership and paved parking areas. There are underground utilities within the nearby streets and servicing the existing facility. The site is bounded by Auto Center Drive to the south, La Quinta Drive to the east, Highway 111 to the north and developed commercial properties to the west. Based on our review of, the USGS (1980), the site is situated at an approximate elevation of 40 feet above mean sea level (AMSL). No natural ponding of water or surface seeps were observed at or near the site during our investigation conducted on August 1.4, 2010. Site drainage appears to be controlled via sheet flow and surface infiltration. Regional drainage is provided by the Whitewater River Channel that is located approximately 1/4 mile north of the site. Sladden Engineering August 20, 2010 .3 - GEOLOGIC SETTING Project No. 54.4.-1.0113 10-08-190 The project site is located within the Colorado Desert Physiographic Province (also referred to as the Salton Trough) that is characterized as a northwest -southeast trending structural depression extending from the Gulf of California to the Banning Pass. The Salton Trough is dominated by several northwest trending faults, most notably the San Andreas Fault system. The Salton Trough is bounded by the Santa Rosa — San Jacinto Mountains on the southwest, the San Bernardino Mountains on the north, the Little San Bernardino - Chocolate Orocopia Mountains on the east, and extends through the Tmperial Valley into the Gulf of California on the south. A relatively thick sequence (20,000 feet) of sediment have been deposited in the Coachella Valley portion of the Salton Trough from Miocene to present times. These sediments are predominately terrestrial in nature with some lacustrian (lake) and minor marine deposits. The major contributor of these sediments has been the Colorado River. The mountains surrounding the Coachella Valley are composed primarily of Precambrian metamorphic and Mesozoic "granitic' rock. The Salton Trough is an internally draining area with no readily available outlet to Gulf of California and with portions well below sea level (-253' msl). The region is intermittently blocked from the Gulf of California by the damming effects of the Colorado River delta (current elevation +3(Ymsl). Between about 300AD and 1600 AD (to 1700 ?) the Salton Trough has been inundated by the River's water, forming ancient Lake Cahuilla (max. elevation +58' msl). Since that time the floor of the Trough has been repeatedly flooded with other "fresh'Water lakes (1849, 1861, and 1891), the most recent and historically long lived being the current Salton Sea (1905). The sole outlet for these waters is evaporation, leaving behind vast amounts of terrestrial sediment materials and evaporite minerals. The site has been mapped by Rogers (1965) to be immediately underlain by undifferentiated Quaternary - age sand deposits (Qs). The regional geologic setting for the site vicinity is presented on the Regional Geologic Map (Figure 2). SUBSURFACE CONDITIONS The subsurface conditions at the site were investigated by drilling four (4) exploratory boreholes to a maximum depth of 51.5 feet bgs. The approximate locations of the boreholes are illustrated on the Borehole Location Plan (Figure'3). The boreholes were advanced using a truck -mounted Mobile B -6T drill rig equipped with 8 -inch outside diameter (O.D.) hollow stem augers. A representative of Sladden was on-site to log the materials encountered and retrieve samples for laboratory testing and engineering analysis. During our field investigation earth materials consisting of silty sand (SM) and sand (SP) were encountered. Granular materials appeared loose to medium dense, moist and fine-grained. Detailed descriptions of the subsurface materials encountered are included in Appendix A of this report. Groundwater was not encountered to a maximum explored depth of 51.5 feet bgs during our field investigation conducted cin' August 14, 2010. As such, it is our opinion that groundwater should not be a factor during construction of the proposed project. Sladden Engineering I August 20, 2010 .4- Project No. 544-10113 10-08-190 SEISMICITY AND FAULTING The southwestern United States is a tectonically active and structurally complex region, dominated by northwest trending dextral faults. The faults of the region are often part of complex fault systems, composed of numerous subparallel faults which splay or step from main fault traces. Strong seismic shaking could be produced by any of these faults during the design life of the proposed project. We consider the most significant geologic hazard to the project to be the potential for moderate to strong seismic shaking that is likely to occur during the design life of the project. The proposed project is located in the highly seismic Southern California region within the influence of several fault systems that are considered to be active or potentially active. An active fault is defined by the State of California as a "sufficiently active and well defined fault" that has exhibited surface displacement within the Holocene epoch (about the last 11,000 years). A p6tentially active fault is defined by the State as a fault with a history of movement within Pleistocene time (between 11,000 and 1..6 million years ago). As previously stated, the site has been subjected to strong seismic shaking related to active faults that traverse through the region. Some of the more significant seismic events near the subject site within recent times include: M6.0 North Palm Springs (1986), M6.1 Joshua Tree (1992), M7.3 Landers (1992), M6.2 Big Bear (1992) and M7.1 Hector Mine (1999). Table 1 lists the closest known potentially active faults that was generated in part using the EQFAULT computer program (Blake, 2000), as modified using the fault parameters from The Revised 2002 California Probabilistic Seismic Hazard Maps (Cao et al, 2003). This table does not identify the probability of reactivation or the on-site effects from earthquakes occurring on any of the other faults in the region. 'TABLE 1 CLOSEST KNOWN ACTIVE FAULTS Fault Name Distance Km Maximum Event San Andreas - Coachella 8.8 7.2 San Andreas - Southern 8.8 7.2 Burnt Mountain 27.9 6.5 San Andreas - San Bernardino 30.1 7.5 Eureka Peak 29.4 6.4 San Jacinto - Anza 34.1 7.2 San Jacinto - Coyote Creek 34.7 6.8 Pinto Mountain 48.4. 7.2 Sadden Engineering August 20, 2010 .5- Project No, 544-101.13 10-08-190 2007 CBC SEISMIC DESIGN PARAMETERS Sladden has reviewed the 2007 California Building Code (CBC) and summarized the current seismic design parameters for the proposed structure. The seismic design category for a structure may be determined in accordance with Section 1613 of the 2007 CBC or ASCE7. According to the 2007 CBC, Site Class D may be used to estimate design seismic loading for the proposed structures. The period of the structures should be less than 'it second. This assumption should be verified by the project structural engineer. The 2007 CBC Seismic Design Parameters are,summarized below. Occupancy Category (Table 1604.5):11 Site Class (Table 1613.5.5): D Ss (Figure 1613.5.1):1.500g S1 (Figure 16135.1): 0.600g' Fa (Table 1613.5.3(1));1.0 Fv (Table 1613.5.3(2)):1.5 Sins (Equation 16-37 (Fa X Sb)): 1.500g Sml (Equation 16-38 (1:v X Sl)): 0.900g SDS (Equation 16-39 12/3 X Smsl): 1.00Og $[X (Equation 16-90 (2/3 X Sm1)): 0.6008 Seismic Design Category: D . GEOLOGIC HAZARDS The subject site is located in an active seismic zone and will likely experience strong seismic shaking during the design life of the proposed project. In general, the intensity of ground shaking will depend on several factors including: the distance to the earthquake focus, the earthquake magnitude, the response characteristics of the underlying materials, and the quality and type of construction. Geologic hazards and their relationship to the site are discussed below, I. Surfam Rupture. Surface rupture is expected to occur along preexisting, known active fault traces. However, surface rupture could potentially splay or step from known active faults or rupture along unidentified traces. Based on our review of :Rogers (1965), Jennings (1994), Bart and Bryant (1997), and RCLIS (2010), no known faults arc currently mapped immediately adjacent to the site. In addition, no signs of active surface faulting were observed during our review of non -stereo digitized photographs of the site and site vicinity (Google, 2010; Terra Server 2002). Finally, no signs of active surface fault rupture or secondary seismic effects (lateral spreading, lurching etc.) were identified on-site during our field investigation. Therefore, it is our opinion that risks associated with primary surface ground rupture should be considered "low". 11. Ground Shaking. The site has been subjected to past ground shaking by faults that traverse through the region. Strong seismic shaking from nearby active faults is expected to produce strong seismic shaking during the design life of the proposed project. A probabilistic approach was employed to the estimate the peak ground acceleration (a.) that could be experienced at the site. Based on the USGS Probabilistic Hazard Curves (USGS, 2009) the site could be subjected to ground motions on the order of 0.56g. The peak ground acceleration at the site is judged to have a 475 year return period and a 10 percent chance of exceedence in 50 years. Sfadden Engineering August 20, 2010 - 6 - Project No. 544-10113 10-08-190 M. Liquefaction. Liquefaction is the process in which loose, saturated granular soil loses strength as a result of cyclic loading. The strength loss is a result of a decrease in granular sand volume and a positive increase in pore pressures. Generally, liquefaction can occur if all of the following conditions apply: liquefaction -susceptible soil, groundwater within a depth of 50 feet or less, and strong seismic shaking. According to the County of Riverside, the site is situated within a "Moderate" liquefaction potential zone (.RCLIS, 2010). Eased on our review of groundwater maps of the site vicinity (>50 feet bgs; Tyley, 1975), and our experience in the project vicinity, risks associated with liquefaction and liquefaction related hazards should be considered negligible. IV. Tsunamis_and_Seichcs. Because the site is situated at an inland location, and is not immediately adjacent to any impounded bodies of water, risk associated with tsunamis and seiches is considered negligible. V. Slope Failure. Landsliding. Rock Falls. No signs of slope instability in the form of landslides, rock falls, earthflows or slumps were observed at or near the subject site. The site is situated on relatively flat ground and not immediately adjacent to any slopes or hillsides. As such, risks associated with slope instability should be considered negligible. Vi. Expansive Soil. Generally, the site soil consists of silty sand (SM) and sand (SP). Based on the results of.our laboratory testing (131-1), the materials underlying the site are considered to have a "very low" expansive potential and risks of structural damage caused by volumetric changes in the subgrade soil is considered "negligible". VII. Settlement. Settlement resulting from the anticipated foundation loads should be tolerable provided that the recommendations included in this report are considered in foundation design and construction. The estimated ultimate settlement is calculated to be less that' approximately one inch when using the recommended bearing values. As a practical matter, differential settlement between footings - can be assumed as one-half of the total - settlement. VIII. Subsidence. The site situated within a. "Active" subsidence zone (RCLJS, 2010). Land subsidence can occur in valleys where aquifer systems have been subjected to extensive groundwater pumping, such that groundwater pumping exceeds groundwater recharge. Cenerally, pore water reduction can result in a rearrangement of skeletal grains and could result in elastic (recoverable) or inelastic (unrecoverable) deformation of an aquifer system. Recent published literature indicates that the Upper Coachella Valley region between 1996 and 2005 has been subjected to groundwater withdrawal related subsidence (USCS, 2007). Although recent investigations have documented significant subsidence within the La Quinta area (USGS, 2007), no fissures or other surficial evidence of subsidence were observed at the subject site. With the exception of isolated tension zones typically manifested on the ground surface as fissures and/or ground cracks, subsidence related to groundwater depletion is generally areal in nature with limited differential settlement over short distances such as across individual buildings. Sledden Engineering August 20, 2010 .77 Project No. 544-10113 10-08-190 "I7ie Coachella Valley Water District has publically acknowledged regional subsidence throughout the southern portion of the Coachella Valley and has indicated a commitment to groundwater replenishment programs that are intended to limit future subsidence. At this time, subsidence is considered a regional problem requiring regional mitigation not specific to the project vicinity. Locally, no fissures or other surficial evidence of subsidence were observed at or near the subject site. However, site specific effects resulting from long term regional subsidence is beyond the scope of our investigation, M Debris Flows. Debris flows are viscous flows consisting of poorly sorted mixtures of sediment and water and are generally initiated on slopes steeper than approximately six horizontal to one vertical (6H:1 V)(Boggs, 2001), Based on the flat nature of the site and the composition of the surface soil, we judge that risks associated with debris flows should be considered remote. X. Flooding and Erosion. No signs of flooding or erosion were observed during our field investigation conducted on August 14, 2010. Accordingly, risks associated with flooding and erosion should be considered low. CONCLUSIONS Based on the results of our investigation, it is our professional opinion that the project is feasible from a soil mechanic's standpoint provided the recommendations of this report are incorporated in the design and carried out through construction..The main geotechnical concern in the construction of the proposed project is the presence of potentially compressible surface soil. Some of the near surface soil underlying the site is considered loose, potentially compressible and not suitable for support of shallow foundations or concrete slabs in its existing condition. Because of the somewhat loose and potentially compressible condition of some of the near surface soil, remedial grading including overexcavation or recompaction is recommended for the proposed new building .and foundation areas. We recommend -that remedial grading within the proposed new building areas include overexcavation and recompaction of the foundation bearing soil. Specific recommendations for site preparation are presented in the Earthwork and Grading section of this report. Caving did occur to varying degrees within each of our exploratory bores and the surface soil may be susceptible to caving within deeper excavations. All excavations should be constructed in accordance with the normal CalOSHA excavation criteria. On the basis of our observations of the materials encountered, we anticipate that the subsoil will conform to that described by CalOSHA as Type B or C. Soil conditions should be verified in the field by a "Competent person" employed by the Contractor. The following recommendations present more detailed design criteria that have been developed on the basis of our, field and laboratory investigation. Sladden Engincedng August 20, 2010 - 8 - Project No. 544-10113 10-0!3-190 EARTHWQRK,AND GRADING All earthwork including excavation, backfill and preparation of the subgrade soil, should be performed in accordance with the geotechnical recommendations presented in this report and portions of the local regulatory requirements, as applicable. All earthwork should be performed under the observation and testing of a qualified soil engineer. The following geotechnical engineering recommendations for the proposed project are based on observations from the field investigation program, laboratory testing and geotechnical engineering analysis. i a, Strig�ing, Areas to be graded should be cleared of any existing pavement, utilities, vegetation, associated root systems, and debris,,All areas scheduled to receive fill should be cleared of old fills and any irreducible matter. The strippings should be removed off site, or stockpiled for later use in landscape areas. Voids left by removals should be properly backfilled in accordance with the compaction recommendations of this report. S b. Preparation of the Building Areas. In order to achieve a firm and unyielding bearing surface, we recommend overexcavation and recompaction throughout the building areas. All native low density near surface soil should be removed to a depth of at least 3 feet below existing grade or 3 feet below the bottom of the footings, whichever is deeper. Remedial grading should extend laterally, a minimum of five feet beyond the building perimeter where possible. The exposed surface should then be scarified, moisture conditioned to within two percent of optimum moisture, content, and compacted to at least 90 percent relative compaction. Testing of the native soil within the excavation bottoms should be performed during grading to verify adequacy. C. Compaction, Soil to be used as engineered fill should be free of organic material, debris, and other deleterious substances, and should not contain irreducible matter greater than three inches in maximum dimension. All fill materials should be placed in thin lifts, not exceeding six inches in their loose state. If import fill is required, the material should be of a low to non -expansive nature -and should meet the following criteria: Plastic Index Less than 12 Liquid Limit Less than 35 Percent Soil Passing 11200 Sieve Between 15% and 35% Maximum Aggregate Size 3 inches The subgrade and all fills should be compacted with acceptable compaction equipment, to at least 90 percent relative compaction. The bottom of the exposed subgrade should be observed by a representative of Sladde'n Engineering prior to fill placement, Compaction testing should be performed on all lifts in order to ensure proper,placement of the fill materials. Table 2 provides a summary of the excavation and compaction recommendations. Sladden Engineering August 20, 2010 .9. Project No. 544-10113 10-08-190 Table 2 SUMMARY OF RECOMMENDATIONS *Remedial Grading Excavation and recompaction within the building envelope and extending laterally for 5 feet beyond the building limits and to a minimum of 3 feet below existing grade or 3 feet below the bottom of the footin , whichever is deeper. Native / Import Engineered Fill Place in thin lifts not exceeding 6 inches in the loose state, compact to a minimum of 90 percent relative compaction within 2 percent of the optimum moisture content. Pavement Areas and Concrete Flatwork Compact the top 12 inches to at least 95 percent compaction within 2 percent of optimum moisture content. *Actual depth may vary and should be determined by a representative of Sladden Engineering in the field during construction. d. Shrinkage and Subsidence. Volumetric'shrinkage of the material that is excavated and replaced as controlled compacted fill should be anticipated. We estimate that this shrinkage could vary from 10 to 20 percent Subsidence of the surfaces that are scarified and compacted should be between 1 and 2 tenths of a foot. This will vary depending upon the type of equipment used, the moisture content of the soil at the time of grading and the actual degree of compaction attained. FOUNDATION CONVENTIONAL SPREAD FOOTINGS Load bearing walls may be supported on continuous spread footings and interior columns may be supported on isolated pad footings. All footings should be founded upon properly engineered fill and should have a minimum embedment depth of 12 inches measured from the lowest adjacent finished grade. Continuous and isolated footings should have a minimum width of 12 inches and 24 inches respectively. Continuous and isolated -footings placed on such materials may be designed using an _ allowable (net) bearing pressure of 1800 and 2000 pounds per square foot (psf) respectively. Allowable increases of 250 psf for each additional 1 foot in width and 250 psf for each additional 6 inches in depth may be utilized, if desired. The maximum allowable bearing pressure should be 2,500 psf. The maximum bearing value applies to combined dead and sustained live loads. The allowable bearing pressure may be increased by one-third when considering transient live loads, including seismic and wind forces. All footings should be reinforced in accordance with the project structural engineer's recommendations. Based on the allowable bearing pressures recommended above, total settlement of the shallow footings are anticipated to be less than one -inch, provided foundation preparations conform to the recommendations described in this report. Differential settlement is anticipated to be approximately half the total settlement for similarly loaded footings spaced up to approximately 40 feet apart. Lateral load resistance for the spread footings will be developed by passive soils pressure against the sides of the footings below grade and by friction acting at the base of the concrete footings bearing on compacted fill. An allowable passive pressure of 300' psf per foot of depth may be used for design purposes. Sladden Engineering August 20, 2010 _10- Project No. 544-10113 10-08-190 An allowable coefficient of friction 0.45 may be used for dead and sustained live loads to compute the frictional resistance of the footing placed directly on compacted fill. Under seismic and wind loading conditions, the passive pressure and frictional resistance may be increased by one-third. All footing excavations should be observed by a representative of the project geotechnical consultant to verify adequate embedment depths prior to placement of forms, steel reinforcement or concrete. The excavations should be trimmed neat, level and square. All loose, disturbed, sloughed or moisture - softened soils and/or any construction debris should be removed prior to concrete placement. Excavated soil generated from footing and/or utility trenches should not be stockpiled within the building envelope or in areas of exterior concrete flatwork, SLABS -ON -GRADE In order to reduce the risk of cracking and settlement, concrete stabs -on -grade must be placed on properly compacted fill as outlined in the previous sections. The slab subgrades should remain near optimum moisture content and should not be permitted to dry. Prior to concrete pour, all slab subgrades should be firm and unyielding. Disturbed soils should be removed and then replaced and compacted to a minimum of 90 percent relative compaction. Slab thickness and reinforcement should be determined by the structural engineer. We recommend a minimum slab thickness of 4.0 inches. All slab reinforcement should be supported on concrete chairs to ensure that reinforcement is placed at slab mid -height. Slabs with moisture sensitive surfaces should be underlain with a moisture vapor retarder consisting of a polyvinyl chloride membrane such as 10 -mil Visqueen, or equivalent. All laps within the membrane should be sealed and at least 2 inches of clean sand should be placed over the membrane to promote uniform curing of the concrete. To reduce the potential for punctures, the membrane should be placed on a pad surface that has been graded smooth without any sharp protrusions. If a smooth surface can not be achieved by grading, consideration should be given to placing a 1 -inch thick leveling course of sand across the pad surface prior to placement of the membrane. PRELIMINARY PAVEMENT DESIGN Asphalt concrete pavements should be designed in accordance with Topic 608 of the Caltrans Highway Design Manual based on R -Value and Traffic Index. Design R -Value is assumed to be 50. On-site and any imported soils should be tested for R -Value. Actual R -Value of subgrade soil should be consistent with the pavement design. For Pavement design, Traffic Indices (Tl) of 5.0 and 6.5 were used for the light duty and heavy duty pavements, respectively. We assumed Asphalt Concrete (AC) over Class IT Aggregate Base (AB). The preliminary flexible pavement layer thickness is as follows: RECOMMENDED ASPHALT PAVEMENT SECTION LAYER THICKNESS Pavement Material Recommended Thickness 71=5.0 TI -6.5 As halt Concrete Surface Course 3 inches 4 inches Class H Aggregate Base Course 4 inches 6 inches Com acted Subgrade Soil 12 inches 12 inches Sladden Englneedng v, August 20, 201.0 -11- Project No. 544-10113 10-08-190 Asphalt concrete should conform to Sections 203 and 302 of the latest edition of the Standard Specifications for Public Works Construction ("Greenbook"). Class II aggregate base should conform to Section 26 of the Caltrans Standard Specifications, latest edition. The aggregate base course should be compacted to at least 95 percent of the maximum dry density as determined by ASTM Method D 1557. SOLUBLE SULFATES Soluble sulfate concentrations were determined to be "negligible" (less than 1,000 ppm) based upon our laboratory testing. Based upon our preliminary testing the use of Type V and/or sulfate resistant mix design should not be necessary. However, the soil should to be retested for soluble sulfate concentration after grading and compaction work is completed. Soluble sulfate content of the surface soil should be reevaluated after grading and appropriate concrete mix designs should be established based upon post - grading test results. UTILITY TRENCH BACKFILL All utility trench backfill should be compacted to a minimum relative compaction of 90 percent. Trench backfill materials should be placed in lifts no greater than six inches in their loose state, moisture conditioned (or air-dried) as necessary to achieve near optimum moisture conditions, and then mechanically compacted in place to a minimum relative compaction of 90 percent. A representative of the project soil engineer should test the backfill to verify adequate compaction. EXTERIOR CONCRETE FLATWORK To minimize cracking of concrete flatwork, the subgrade soil below concrete flatwork areas should first be compacted to a minimum relative compaction of 90 percent. A representative of the project geotechnical consultant should observe and verify the density and moisture content of the soil prior to concrete placement. DRAINAGE All final grades should be provided with positive ..gradients away from foundations to provide rapid— removal of surface water runoff to an adequate discharge point. No water should be allowed to be pond on or immediately adjacent to foundation elements. In order to reduce water infiltration into the subgrade soil, surface water should be directed away from building foundations to an adequate discharge point. Subgrade drainage should be evaluated upon completion of the precise grading plans and in the field during grading. Sladden Engineering August 20, 2010 -12 - Project No. 544-10113 10-08-190 LIMITATIONS The findings and recommendations presented in this report are based upon an interpolation of the soil conditions between the exploratory boring locations and extrapolation of these conditions throughout the proposed building area. Should conditions encountered during grading appear different than those indicated in this report, this office should be notified. The use of this report by other parties or for other projects is not authorized. The recommendations of this report are contingent upon monitoring of the grading operation by a representative of Sladden Engineering. All recommendations are considered to be tentative pending our review of the grading operation and additional testing, if indicated. If others are employed to perform any soil testing, this office should be notified prior to such testing in order to coordinate any required site visits by our representative and to assure indemnification of Sladden Engineering. We recommend that a pre -job conference be held on the site prior to the initiation of site grading. The purpose of this meeting will be to assure a complete understanding of the recommendations presented in this repoit as they apply to the actual grading performed. ADDITIONAL SERVICES Once completed, final project plans and specifications should be reviewed by use prior to construction to confirm that the full intent of the recommendations presented herein have been applied to design and construction. Following review of plans and specifications, observation should be performed by the Soil Engineer during construction to document that foundation elements are founded on/or penetrate into the recommended soil, and that suitable backfill soil is placed upon competent materials and properly compacted at the recommended moisture content. Tests and observations should be performed during grading by the Soil Engineer or his representative in order to verify that the grading is being performed in accordance with the project specifications. Field density testing shall be performed in accordance with acceptable ASTM test methods. The minimum acceptable degree -of compaction should be 90 percent for subgrade soils and 95 -percent for Class lI aggregate base as obtained by the ASTM D1557-91 test method. Where testing indicates insufficient density, additional compactive effort shall be applied until retesting indicates satisfactory compaction. Sladden Engineering August 20, 2010 -13- Project No. 5.4.4-1.0113 10-08-190 REFERENCES Blake, T., 2000, EQFAULT and EQSEARCH, Computer Programs for Deterministic and Probabilistic Prediction of Peak Horizontal Acceleration from Digitised California Faults. Boggs, S. Jr., (2001), "Principles of Sedimentology and Stratigraphy", Prentice Hall, third edition California Building Code (CBC), (2007), California Building Standards Commission. Cao T., Bryant, W.A., Rowshandel B., Branum D., Wills C.J., (2003), "The Revised 2002 California Probabilistic Seismic Hazard Maps". GoogleEarth.com, 2010, Vertical Aerial Photograph for the La Quinta area, California, Undated, Variable Scale. Hart, E. W., and Bryant, W. A., Revised 1997, Fault -Rupture Hazard Zones in California, Mquist-Nolo Earthquake Fault Zoning'Act with Index to Earthquake Fault Zones Maps: State of California, Department of Conservation, Division of Mines and Geology Special Publication 42. 38 Pages. Supplements 1 and 2 were added on 1999. Jennings, Charles W. (Compiler), 1994, Fault Activity Map of California and Adjacent Areas, California Division of Mines and Geology, Geologic Data Map No. 6 Riverside County Land Information Systems (RCLIS),available at http://www.tlma.co.riverside.ca.us/gis/gisdevelop.htmi. Rogers T.H (compiler), Jenkins, O.P (edition) (1965), Geologic Map of California, Santa Ana Sheet, sixth printing 1992, California Division of Mines and Geology, 1: 250,000. TerraSever, Inc., 2002, Aerial Photographs and 'I'opographic Maps at Various Scales. Available at - - www.terraserve.com - - - - Tyley, S.J., (1974) Analog Model Study of the Ground -Water Basin of the Upper Coachella Valley, California, Geological Survey Water-Suppley Paper 2027. United States Geological Survey (USGS) (1980) La Quinta 7.5 Minute Quadrangle Map, 1:24000. United States Geological Survey (USGS) (2007), "Detection and Measurement of land Subsidence Using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, California, 1996-200Y, Scientific Investigations Report 2007-5251. United States Geological Survey (USGS) (2009), "Seismic Hazard Curves and Uniform Response Spectra, Version 5.0.9a", updated 10/21/2009. Sadden Engineering } FIGURES SITE I'.00ATION MAP REGIONAL GEOLOGIC MAP BOREHOLE LOCATION PLAN •r Siodden Engineering i } FIGURES SITE I'.00ATION MAP REGIONAL GEOLOGIC MAP BOREHOLE LOCATION PLAN •r Siodden Engineering 010r,0Z 4mgny � - va"vIS 061-9"T 1�N E1101 -M ZA"WnN Palma JVW NOLLVD01 MS ---'jn ---• - ,� 11 (0861) S��:aunos 9� :• I�-o�- -� ..-- aig Cot IteM Iii f \ ; 118* F . • �, , ,: ° • Y� 11,, M td MIIIJI • � -I • ... a' p � •�G • �i r 1�• rr lap pro . - L rb Xdd N.. ..�.--� �•y�� ti'"'}:" :.v�•� \ . 1 11 � I:� it i; � � ^ ^�� �r '�'� •1.:1:1:5•:::.•.,.. 1 � � •! 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AJC '....�- j a _ +d�c�3:�::.:.ii�..:._.1�m" 1��:_C•.:. ti�.'?'�P .�.,L I j � ;lei Il�I-' '�li�l_�; �--•--� 41 �� I!� � •-� `111!11:: __J I. • 11%3'1 SQ fT I- ..—. iliii 37 •� s —� L �- I W_ I ` 1wM M I� Wcon i l i i SJ. ITE PLAN " -- - --�� �_ �` •—�% r' i � oenre • ��-. �. SBjj..4 Approximate Borehole Location and Designation BOREHOLE LOCATION PLAN Pmiec* Numfmq- 1 544-10113 it FIGURE 3 r e NOJJ,V'601dXH a131d V XIQNBddV t r„ APPENDIX A FIELD EXPLORATION For our field investigation four (4) exploratory bores were excavated utilizing a truck mounted hollow stem auger rig (Mobile B-61). Continuous logs of the materials encountered were made by a representative of Sladden Engineering. Materials- encountered in the boreholes were classified in accordance with the Unified Soil Classification System which is presented in this appendix. Representative undisturbed samples were obtained within our borings by driving a thin-walled steel penetration sampler (California split spoon sampler) or a Standard Penetration Test (SPT) sampler with a 140 pound automatic -trip hammer dropping approximately 30 inches (ASTM D1586). The number of blows required to drive the samplers 18 inches was recorded in 6 -inch increments and blowcounts are indicated on the boring logs. The California samplers are 3.0 inches in diameter, carrying brass sample rings having inner diameters of 2.5 inches. The standard penetration samplers are 2.0 inches in diameter with an inner diameter of 1.5 inches. Undisturbed samples were removed from the sampler and placed in moisture sealed containers in order to preserve the natural soil moisture content. Bulk samples were obtained from the excavation spoils and samples were then transported to our laboratory for further observations and testing. . ;, , Sladden Engineering UNIFIED SOIL CLASSIFICATION SYSTEM MAJOR DIVISIONS TXPICAL NAMES [s7 CLEAN GRAVELS GW WELL GRADED GRAVEL -SAND MIXTURES GRAVELS WITH LITTLE OR NO v1 FINES, GP POORLY GRADED GRAVELS, GRAVET; SAND MIXTURES q° MORE THAN HALF FRACTION GM SILTY GRAVELS, POORLY -GRADED GRAVEL- z COARSE IS SAND -SILT MUCr ORES 0 x LARGER THAN No.4 SIEVE GRAVELS WITH OVER CLAYEY GRAVELS, POORLY GRADED GRAVEL• I" Ca x SIZE .12% FINES zGC SAND -CLAY MIXTURES cd SW WELL GRADED SANDS, GRAVELLY SANDS m w G_ SANDS CLEAN SANDS WITH LI7rLE OR NO FINES c� x SP POORLY GRADED SANDS, GRAVELLY SANDS SILTY SANDS, POORLY GRADED SAND -SILT FMORE THAN HALF w COARSE FRACTION IS SM MIXTURFS SMALLER THAN N%4 SANDS WITH OVER SIEVE SIZE 12% FINES Sc CLAYEY SANDS, POORLY GRADED SAND -CLAY MIXTURES INORGANIC SILTS & VERY FINE, SANDS, ROCK ML FLOUR, STL'1'Y OR CLAYEY FINE SANDS, OR CLAYEY SILTS WITH SLIGHT PLASTICITY F' SILTS AND CLAYS INORGANIC CLAYS OF LOW TO MEDIUM ,.� LIQUID LIMIT LESS THAN 5U CL PLASTICITY, GRAVELLY CLAYS, SANDY CLAYS SILTY CLAY$ CLEAN CI..AYS OL ORGANIC CLAYS AND ORGANIC SILTY CLAYS a ell OF LOW FLASTICITY M CA INORGANIC SILTS, MICACEOUS OR xc MH T)TATOMACIOUS FINE SANDY OR SILTY SOILS, z ELASTIC SILTS CH INORGANIC CLAYS OF HIGH PLASTICITY, FAT ru SILTS AND CLAYS: LIQUID L1MPr GREATER THAN 50 CT.AYS GH ORGANTC CT.AYS OF MEDIUM TO HIGH J O PLASTICITY, ORGANIC SILTS HIGHLY ORGANIC SOILS Pt PEAT AND OTHER HIGHLY ORGANIC SOILS EXPLANATION OF BORE LOG SYMBOLS -California Split -spoon Sample ®Unrecovered Sample Standard Penetration Test Sample Note: The stratification lines on the boretogs represent the approximate Groundwater depth boundaries between the soil types; the transitions may be gradational. A-1 BORE LOG SLADDIEN ENGINEERING Drill Pig: Mobil B-69 Date Drilled: 8/14/2010 Elevation: 68 Feet (MSL) Boring No: BH-1 It o� a o 6 Description Q. o in m t� � aQ C7 Silty'Sand (SM); light yellowish brown, moist, fine-grained (Fill). 2 ............ M14i:Y ' .......u.u.u...u.u.uu.u...u........u.uu....u.u.u.u.uu...........:.........u.u.u.u.u.u.u.u.u.u.........u.__.__.___.-.-_ 4 4/6%7 15.8 2.0 99.4 6 Silty Sand (SM); light yellowish brown, dry, loose, fine-grained (Qal), 8 3/3/3 2.8 2.4 10 Sand (SP); light yellowish brown, dry, loose, fine-grained (Qal), 1.2 418/8 t 42.2 10.1 95.1 16 E' Silty Sand (SM); light yellowish brown, moist, loose, fine-grained with clay (Qal). 18 7/8/10 \ 19.2 4.6 -::!::::::::Silty Sand (SM); light yellowish brown, moist medium dense, fine- 22 grained (Qal), 24 5/8/11 i 27.2 6.8 105.026 Silty Sand (SM); light yellowish browny moist, medium dense, fine- grained (Qal). 28 9/8/5 10.1 3.6 34) ::::: Sand (SP); light yellowish brown, moist medium dense, fine-grained 32 : with clay (Qal). 7/8/10 \ 28.2 5.5 � 95.136 34 " Silty Sand (SM); mottled light olive brown and light yellowish brown, moist, medium dense, fine-grained (Qal). 38 10/11/13 11.5 2.6 40— -::::::::::::.Sand Sand (SP); light yellowish brown, dry, medium dense, fine-grained 42 :; (Qal). 44 9/12/12 1 37,5 6.0 70.1,7 46 s ; Silty Sand (SM); light olive brown, moist, medium dense, fine-grained (Qal)- 48 5/5/4 1 60.8 1 14.7 5affffy—bILE ; 011Ve DAMKITUIsCs w Plasticity, (Qal). Completion Notes: PROPOSED CHEVROLET/CADILLAC DEALERSHIP 2.5"AC over 2.5" Base 79225 HIGHWAY 111, LA QUINTA, CALIFORNIA Terminated at 51.5 Feet bgs Project MY 544-10113 No Bedrock/Groundwater/Seepage Encountered. Page 7 Re rt No: 10-08-190 BORE LOC SLADDEN ENGINEERING Drill Rig: Mobil 13.61 Date Drilled: 8/14/2010 Elevation: 68 Feet (MSL) Boring No: BH -2 b .� g V Description LJ u5 G •o � .0 .E v� ca rra w aE aQ O . Silty Sand (SM); light yellowish brown, moist fine-grained (Fill). 2/3/4 i 14.3 3.0 4 6 • Silty Sand (SM); light yellowish brown, moist, loose, fine-grained 8 2/4/3 37.5 9.8 t0 ii -Silty Sand (SM); light yellowish brown, moist, loose, fine -trained 12 • (Qal)., 14 5/7/7 9.8 3.5 16 :: ::: Sand (SP); light yellowish brown, moist medium dense, fine•grained (Qal)• 18 20 Sand (SP); light yellowish brown, moist, medium dense, finagrained 3/5/7 9.0 4.9 (Qal) 22 24 Terminated at -21.5 Feet. No Bedrock Encountered. No Groundwater or Seepage Encountered. -28- 830343684024446.Y8Completion -30- -34- _36- -38- -40- -42- -44- 46:- -48- CompletionNotes: PROPOSED CHEVROLET/CADILLAC DEALERSHIP 2.5"AC over 3.0" Bose 79225 HIGHWAY 111, LA QI.IINPA, CALIFORNIA Project No: 544-10113 Page 2 Report No: 10-08-190 BORE LOG SLADDEN ENGINEERING Drill Rig: Mobil B-61 Date Drilled: 8/14/2010 Elevation: 68 Feet (MSI.) Boring No: BH -3 cn oy o $ o Description `vpi ao m a8 3$ Silty Sand (SM); light yellowish brown, moist, fine-grained (Fill). . 2 4. r.. — ------------------------------------- ------------------------------------- ....—.—......... .................� 4 5/7/8 1(� 15.6 3.2 106.7 :. Silty Sand (SM); light yellowish brown, moist, loose, fine-grained (tel) _ 8 3/3/3 9.5 1 10 :; Sand (SP); light yellowish brown moist, loose, fine-grained (Qal). 12 14 5/8/8 V 10.1 2.7 16 :':•:• Sand (SP); light yellowish brown, moist, loose, fine-grained (Qal). 1R 617/7 �� 26.4 3.7 20 . Silty Sand (SM); light yellowish brawn, moist, medium dense, firer 22 grained (Qal). j 24 5/5/7 AV 30.9 5.7 43.4 26 Silty Sand (SM); light yellowish brown, moist, louse, fine-grained, micaceous (Qal). 28 30 Silty Sand (SM); light yellowish brown, moist, medium dense, fine - 6/8/9 20.9 2.0 grained (Qal). 32 �4 Terminated at -•31.5 Feet. No Bedrock Encountered. 36 No Groundwater or Seepage Encountered. 38 40 42 44 46 48 50 Completion Note~: PROPOSED CHEVROLE /CADILLAC DEALERSHIP 5"AC over 5.0" Base 79225 HIGHWAY 111, LA QUINTA, CALIFORNIA Project No: 544-10113 Page $ Report No: 10-08-190 BORE LOG SLADDEN ENGINEERING Drill Rig, Mobil B-61 Date Drilled: 8/14/2010 Elevation: 68 Feet (MSI.) Boring No: BH -4 U 21 5 c Description 0/ E f c Silty,Sand (SM); light yellowish brown, moist, fine-grained (Fill). 2 - -----•--•--•-•---•--•- .................................................... 4 4/6/6 11.2 21 6 :;:;. Sand (SP); yellowish brown, dry, medium dense, fine-grained (Qal). A 3/5/5 10 10 No Recovery 12 ' 14 'Terminated at •-11.5 Feet. No Bedrock Encountered, 16 No Groundwater or Seepage Encountered. 18 20 22 24 26 28 30 34 36 40 42 44 46 48 50 Completion Notes: PROPOSED CT-TEVROLET/CADiLLAC DEALERSHIP 3"AC over 7.0" Base 79225 HIGHWAY 111, LA QUINTA, CALIFORNIA Project No: 544-10113 Page Report No: 10--190 APPENDIX B LABORATORY TESTING Sladden Engineering APPENDDC B LABORATORY TESTING Representative bulk and relatively undisturbed soil samples were obtained in the field and returned to our laboratory for additional observations and testing. Laboratory testing was generally performed in two phases. The first phase consisted of testing in order to determine the compaction of the existing natural soil and the general engineering classifications of the soils underlying the site. This testing was performed in order to estimate the engineering characteristics of the soil and to serve as a basis for selecting samples for the second phase of testing. The second phase consisted of soil mechanics testing. This testing including consolidation, shear strength and expansion testing was performed in order to provide a means of developing specific design recommendations based on the mechanical properties of the soil. CLASSIFICATION AND COMPACTION TESTING Unit Weight and Moisture Content Determinations: &ch undisturbed sample was weighed and measured in order to determine its unit weight. A small portion of each sample was then subjected to testing in order to determine its moisture content. This was used in order to determine the dry density of the soil in its natural condition. The results of this testing are shown on the Boring Logs. Maximum Density -Optimum Moisture Determinations: Representative soil types were selected for maximum density determinations. This testing was performed in accordance with the ASTM Standard D1557-91, Test Method A. The results of these tests are presented graphically in this appendix. The maximum densities are compared to the field densities of the soil in order to determine the existing relative compaction to the soil. Classification Testing. Soil samples were selected for classification testing. This testing consists of mechanical grain size analyses.:.This provides information for developing classifications for the soil in accordance with the Unified Soil Classification System which is presented in the preceding appendix. This classification system categorizes the soil into groups having similar engineering characteristics. The results of this testing is very useful in detecting variations in the soil and in selecting samples for further testing. SOIL MECHANIC'S TESTING Expansion Testing: One (x) bulk sample was selected for Expansion testing. Expansion testing was performed in accordance with the UBC Standard 18-2. This testing consists of remolding 4 -inch diameter by 1 -inch thick test specimens to a moisture content and dry density corresponding to approximately 54 percent saturation. The samples are subjected to a surcharge of 144 pounds per square foot and allowed to reach equilibrium. At that point the specimens are inundated with distilled water. The linear expansion is then measured until complete. Direct Shear Vests: One (1) bulk sample was selected for Direct'Shear Testing. This test measures the shear strength of the soil under various normal pressures and is used to develop parameters for foundation design and lateral design. Tests were performed using a recompacted test specimen that was saturated prior to tests. Tests were performed using a strain controlled test apparatus with normal pressures ranging from Boo to 2300 pounds per square foot. Siadden Engineering Consolidation Test: One (1) relatively undisturbed sample was selected for consolidation testing. For this test, a one -inch thick test specimen was subjected to vertical loads varying from 575 psf to 11.520 psf applied progressively. The consolidation at each load increment was recorded prior to placement of each subsequent load. The specimens were saturated at $75 psf or 720 psf load increment. ti