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04-5178 (SFD) Geotechnical ReportsSladden Engineering - 6782 Stanton Ave., Suite A, Buena Park, CA 90621 (714) 523.0952 Fax (714) 523-1369 39-725 Garand Ln., Sulte G, Palm Desert, CA 92211 (760) 772-3893 Fax (780) 772.3895 March 16, 2004 Dirkson & Associates 9461 Hughes Drive Corona, California 92083 Attention: Mr. Rick Dirkson Project: 52-948 Claret Cove Lot 36 — Tract 28867 Tradition Golf Club La Quinta, California Subject: Ceotechnical Update Project No, 544-4137 04.03.199 Ref: 1, Report of Observations and Testing During Hough Grading prepared by Sladden i Engineering dated July 30,1997, Project No. 522-6138-G1. 2. Geotechnical Update prepared by Sladden Engineering dated December 12, 1996, Project No. 544-6130. As requested, we have reviewed the geotechnical reports previously prepared for the Tradition development as they relate to the design and construction of the proposed residence. The project site is located at 52-948 Claret Cove within the Tradition Colf Club development in the City of La Quinta, California. It is our understanding that the pioposcd residential structure will consist of a relatively lightweight wood frame structure with a subterranean garage level. The propose residence will be supported upon conventional shallow spread footings and concrete slabs on grade. As described within the previous reports, the subject lot was previously graded during the initial rough grading of the Tradition project site. The rough grading included overexcavation of the native surface soils along with the placement of engineered fill material to construct the building pad. The site grading is summarized in the previous grading reports along with the compaction test results. The referenced reports include recommendations pertaining to the construction of residential structure foundations. Based upon our review of the referenced reports, it is our opinion that the structural values included in these reports remain applicable for the design and construction of the proposed residenhal structure foundations. March 16, 2004 -2- Project No, 544-4137 04-03-199 Allowable Bearing Pressures: The structural values recommended in the previous geotechnical reports remain applicable for use in foundation design. Conventional shallow spread footings should be bottomed into properly compacted fill material a minimum of 12 inches below lowest adjacent grade. Continuous footings should be at least 1.2 inches wide and isolated pad footings should be at least 2 feet wide. Continuous footings and isolated pad footings should be designed utilizing allowable bearing pressures of 1800 psf and 2000 psf, respectively. The recommended allowable bearing pressure may be increased by one-third when considering wind and seismic loading. Increases in allowable bearing pressures may be realized with increased footing size. Allowable increase of 200 psf for each additional l foot of width and 250 psf for each additional 6 inches of depth may be utilized, if desired. The maximum allowable bearing pressure should be 3000 psf. Resistance to lateral loads can be provided by a combination of friction acting at the base of the slabs or foundations and passive earth pressure along the sides of the foundations. A coefficient of friction of 0.48 between soil and concrete may be used with dead load forces only. A passive earth pressure of 300 pounds per square foot, per foot of depth, may be used for the sides of footings, which are placed against properly compacted native soils. Retaining basement walls will be required to accomplish the proposed subterranean parking level construction. Cantilever retaining walls may be designed using "active" pressures. Active pressures may be estimated using an equivalent fluid weight of 35 pcf for native backfill soils with level free -draining backfill conditions. The equivalent fluid weight should be increased to 55 pef when designing restrained walls such as the proposed basement walls: The bearing soils are non -expansive and fall within the "very low" expansion category. in accordance with Uniform Building Code (UBC) classification criteria. Pertinent 1997 UBC Seismic Design parameters are summarized on the attached data sheet. Because the lot has been previously graded, the remedial grading required at this time for the proposed residence should be minimal except for the basement area. Because the basement level may extend through the previously placed engineered fill material, additional overexcavation and/or compaction in-place is recommended for the subterranean garage level. The foundation bearing soils throughout the basement area should be properly compacted to a minimum depth of 2 feet below the bottom of the footings to insure that all foundations are bearing upon compacted fill material. The remainder of the building areas should be cleared of surface vegetation, scarified and moisture conditioned prior to precise grading. The exposed surface should be compacted so that a minimum of 90 percent relative compaction is attained prior to fill placement. Any fill material should be placed in thin lifts at near optimum moisture content and compacted to at least 90 percent relative compaction. Sladden Engineering March 16, 2004 .3 - if you have questions regarding this report, please contact the undersigned. Respectfully submitted, SLADDEN ENGINEERING Brett L. Andersoh Principal Engineer SER/pc Copies: 4/Dirkson 6r Associates Project No. 544-4137 04-03-199 Sladden Englneering March 16, 2004 -4- Project No. 544-4137 04-03-199 1997 UNIFORM BUILDING CODE INFORMATION The International Conference of Building Officials 1997 Uniform Building Code contains substantial revisions and additions to the earthquake engineering section in Chapter 16. Concepts contained in the code that will be relevant to construction of the proposed structure are summarized below. Ground shaking is expected to be the primary hazard most likely to affect the site, based upon proximity to significant faults capable of generating large earthquakes, Major fault zones considered to be most likely to create strong ground shaking at the site are listed below. Fault Zone Approximate Distance From Site Fault Type (1997 UBC) San Andreas 13 km A San Jacinto 30 km A Based on our field observations and understanding of local geologic conditions, the soil profile type judged applicable to this site is So, generally described as stiff or dense soil. The site is located within UBC Seismic Zone 4. The following table presents additional coefficients and factors relevant to seismic mitigation for new construction upon adoption of the 1997 code. Slodden Engineering Near -Source Near -Source Seismic Seismic Seismic Acceleration Velocity Coefficient Coefficient Source Factor, N, . Factor, N. C, C. San Andreas 1.0 1 1.1 1 0.44 N. 0.64 N,, San Jacinto 1.0 1 1..0 1 0.4.4. N. 0.64 Nv Slodden Engineering 1 - REPORT OF OBSERVATIONS AND TESTING DURING ROUGH GRADING TRADITION - TRACT 28470 LA QUINTA, CALIFORNIA — Prepared By — Slodden Engineering 6782 STANTON AVE. SUITS E BUENA PARK, CA 906211 (213) 864•.'121 (714) 523-0952 Siodden Engineering Sladden Engineer'i"ng. 6762 Stanton Ave., Suite B. Buena Park. CA 90621 (310) 864-4121 (714) 523-0952 Fax (714) 523-1369 39-725 Garand Ln., Suite G, Palm Desert, CA 92211 (619) 7712-3893 Fax (619) 772-3895 Jule 30, 1997 Project No. 522-6138-G1 Tradition Club Associates, LLC c/o Winchester Development Company 41-865 Boardwalk, Suite 101 Palm Desert, California 92211 Attention: Mr. Mike Rowe Project: Tradition - Tract 28470 La Quinta, California Subject: Report of Obseivations and Testing During Route Grading Ref: Geotechnical Update prepared by Sladden Engineering dated December 12, 1996; Project No. 4446130 Summarized in this report are our observations and the results of in-place density tests performed at the project site during rough grading. The rough grading..consisted of the grading of an eighteen hole golf course surrounded by residential building pads. As indicated in the previous geotechnical reports and; summarized in the referenced Geotechnical Update, portions of the project site including some of the building pads were previously graded in 1988 as part of the East La Quinta Flood' Control project. Due to the varying soils conditions on the site (including previously graded, building pads), the extent of the remedial grading, work performed during rough grading varied across the site. Observations -and field testing was performed during the rough grading operations from January 2,--.1997 to. April 4, 1997. Grading operations were performed by Nuevo Engineering using conventional heavy equipment. A representative of Sladden 1✓ngineeting was present on the site continuously during the grading of building pads and internLattandy during the grading of golf course areas. luiv 30, 1997(2) Project No. 52_-6138-G1 Field Tests: In' -place moisture/density tests were performed using a nuclear density gauge in accordance with test methods ASTM D 2922• and ASTM D-3017. A total of 1417 tests were performed during the initial rough grading. The approximate test locations are indicated on the grading plans includedwith this report and test results are summarized on the attached data sheets. Testing indicates that aminimum of 90 percent re!ative compaction was attained in the areas tested. The passing test results indicate compliance with the project specifications at the tested locations and depths but are no guarantee or warranty of the contractor's work. Laboratory Tests: The moisture -density relationships for the tested materials were determined in the laboratory in accordance with test method ASTM D. 1557-91. Laboratory test results are summarized on the attached data sheet. Discussion: As previously discussed, the remedial grading performed at the site varied with location and soils conditions. Prior to Brading, the building areas were stripped of weeds; brush and other surface vegetafion: "Clearing operations also included the removal of citrus trees and other trees from the lower (nor -them) portion of the site. In general, remedial grading throughout the southern portion of the site consisted of watering and compaction of the native soils in-place .along with the placement of engineered fill material to construct the building pads. Native soils were watered so that near optimum moisture content was attained to a minimum depth of three feet below original grade or four feet below pad grade; whichever was deeper. The exposed surface was compacted so that at least 90 percent relative compaction was attained to a depth of two feet below original grade or three feet below pad Grade, whichever was deeper. In most areas, fill material obtained from the adjacent golf course areas was placed to construct the building pads. Tne lots graded as described above included lots 150 through %_9 and 238 to 241. The maiority of the lots located within the middle portion of the site were previously rough graded. These lots were cleared of weeds and brush and watered prior to trading* in genera!, grading consisted primarily of some minor cuts and fills (some in excess of 10 feet) to achieve the plan elevations. In most cases; the building pads did not ex -tend laterally beyond the previously graded building pads. In areas where the pads were extended substantially (such as along the rear property lines of lots 81 through 84), the fills were initiated within firm native soils near the toe of the slopes. A keyway was established near the toe of the slope and fill soils were benched into the existing slope during placement. The previously graded lots that were regraded as described above include lou 27 through 36 and lou 76 through 150. Slodden Engineering July 30, 1997 (3) Project No. 522-6138-G1 The remedial grading performed throughout the northern portion of the site included overexcavation and recompaction within the building areas. In general; lots were overexcavated to a depth of at least three feet below original grade. The previously removed soils were replaced in. thin lifts and compacted along with fill soils obtained from the nearbv golf course areas to construct the building -pads. The lots that were overexcavated include lots I through 26 and 37 through 75, and the maintenance building \ariz�& , Some of the residential lots have been used for the storage of rock, trees, other construction materials and excess fill soils subsequent to grading. Although some of these lots may require additional cleaning or fine grading„ no degradation of the compacted fill material is expected. Fill material was stockpiled on lots 193 through 207 for use during ,the e g he futurrading of lots 230 through 236. The stockpiled material was not tested . because it will be removed at a later date. irrigation lines were encountered in the area of the existing pond and accessing the pond. The pond was removed during grading but some of the irrigation lines were left in place for future abandonment. These irrigation lines should be removed from building pads and roadway areas when abandonment is allowed. The resulting excavations should be properly bacic-filled and backnll material should be properly compacted. Recommendations: The allowable bearing pressures recommended in the original Geotechnical Engineering Reoort prepared by Buena Engineers, Inc. dated November 27, 1984 (B -14796-P1, 84-11-216) remain applicable. Conventional shallow spread footings should be bottomed in properly compacted fill material at least 12 inches below lowest adjacent glade. Continuous footings should be at least'12 inches wide and isolated pad footings should be at least two feet wide. Continuous footings and isolated pad footings may be designed utilizing an allowable bearing pressures of 1500' psf., .4n allowable increase of 200 psf for each additional six inches of depth may�e utilized if desired. The maximum allowable bearing pressure should be 3000 psf. The recommended allowable bearing pressures may be increased by one-third for wind and seismic loading. Lateral forces may be resisted by friction acting along the base of the foundations and Passive resistance along the sides of the footings. A friction coefficient of 0.45 times the normal dead -load forces is suggested for use in des* gn.• Passive resistance may be estimated using an equivalent fluid weight of 300 pcf. If used in combination, we suggest that either the frcitional resistance or the passive resistance be reduced by one-third. Slodden Engineering Juin 30, 1997 (4) Project No. 522-6138-G1 Cantiiever retaining walls should be designed using "active" pressures. Active pressures may be estimated using an equivalent fluid weight of 35 pcf Walls that are restrained should be designed using "at rest" pressures. At rest pressures may be estimated using an equivalent fluid weight of 55 pdf. The given design pressures are applicable for free - drained level back -fill conditions. The project site is located in a seismically active area and the potential for seismic activity should be considered in building design. In general; the Uniform Building Code requirements for Seismic Zone 4 should be addquate for the design of the planned residential structures. Because some of the site soils (primarily the silty sands and sandy silts encountered throughout the northern portion of the site) may be susceptible to settlements due to the introduction of excess moisture, care should be taken to minimize infiltration adjacent to building foundations. Positive drainage should be provided to direct water away from the structures. The ponding of water adjacent to .buildings or paved areas should not be allowed. Proper grading should be performed to direct stormwater runoff away from structures and landscape irrigation should be minimized Limitations: Sladden Engineering has prepared this report for the exclusive use of the client and it's authorized representatives. This report has been prepared in accordance with generally accepted geotechnicalengineering practices as of this date. No other warranties. either expressed or implied are made. if there are any questions regarding this report or the testing summarized herein, please contact the undersigned. Respectfully submitted, SLADDEN ENGMERING Hogan R. Wright ProjectEngineer Copies: 2_ Brett L. Anders, Principal Engine Tradition Club Associates, LLC Winchester Development Company Siodden Engineering 17, 2 'A T Jul v -10.1 (5) roject No -�22t613&Gl' Nt rqi - 1 1'260, ratory Test Results 1� "Y 7 4;d 4t, "L 41 Gray brown"fine to coarse grained'sand with gravel(SP).-.;.:. i-3 A W Ma)dmum Dry, Density. 127.8 -f /.,Optimum Moisture 70/ -PI, Content -.'8.7/o, 44� Brown'silty fine to coarse grained sand -with grave "I' Iq :(SM) X Maximum Dry. Densityu' a.. 123. 5: pcf im''um' Moisture Content--% pt 7 9 'q Brown slightly silty fine to,coarse grained sand with i�ravel',,(SP) -,,rt Maximum Dry D�nsity;"-"l30;7'pc;f Optimum'Mois=e Conterit 8.7% Y 1 f Brown silty fine ed sand. (SK grain Maximum Dy Density -116.2 Pcf Optimum Moisture, Concent Brown very silty fine gained sand (SM) Maximum Dry Density - I 10. 0 pcf /Optimum I urn Moisture Content - 11.7% Brown silty fine to medium gained sand (SM) Maximum Dry Density - 120.0 Pcf / Optimum Moisture C6 ntent - 8.9% Slodden Engineering