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Home My WebLink AboutCT 07-08; LA COSTA SPA & RESORT VILLAS; GEOTECHNICAL UPDATE; 2008-08-26. . (W Sladden Engineering 77-725 Enfield Lane, Suite 100, Palm Desert, CA 92211 (760) 772-3893 Fax (760) 772-3895 6782 Stanton Avenue, Suite A, Buena Park, CA 90621 (714) 523-0952 Fax (714) 523-1369 450 Egan Avenue, Beaumont, CA 92223 (951) 845-7743 Fax (951) 845-8863 August 29, 2008 Project No. 444-3161 08-08-467 La Costa Resort and Spa do KSL Development Corporation 2100 Costa Del Mar Road Carlsbad, California 92009 Subject: Geotechnical Update Project: Proposed Phase 5 Resort Villas La Costa Resort & Spa Costa Del Mar Road Carlsbad, California Ref: Geotechnical investigation Report prepared by Sladden Engineering dated November 11, 2004, Project No. 444-3161, Report No. 03-10-183. Geotechnical Update prepared by Sladden Engineering dated November 30, 2004; Project No 444-3161, Report No. 04-11-910 As requested, we have reviewed the above referenced Geotechnical Investigation report and update as they relate to the design and construction of the proposed Phase 5 Resort Villas (Buildings 9A and 9B). The site of the proposed Phase 5 Resort Villas is just south of Arenal Road and just east of Estrella De Mar Road within the La Costa Resort and Spa complex in the City of Carlsbad, California. The referenced Geotechnical Investigation report includes recommendations for the design and construction of resort/residential building foundations. Based upon our review of the referenced report and our previous site observations, it is our opinion that the recommendations included in the above referenced report remain applicable for the proposed Phase 5 Resort Villas. Footings should extend at least 18 inches beneath lowest adjacent grade. Isolated square or rectangular footings at least 2 feet square may be designed using an allowable bearing pressure of 2500 pounds per square foot. Continuous footings at least 15 inches wide may be designed using an allowable bearing pressure of 2000 pounds per square foot. Allowable increases of 200 psf for each additional 1 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. The allowable bearing pressures are for dead and frequently applied live loads and may be increased by 1/3 to resist wind, seismic or other transient loading. August 29, 2008 -2- Project No. 444-3161 08-08-467 The recommendations made in the preceding paragraph are based on the assumption that all footings will be supported by properly compacted soil. Prior to the placement of the reinforcing steel and concrete, we recommend that the footing excavations be inspected in order to verify that they extend into the firm compacted soil and are free of loose and disturbed materials. Settlements may result from the anticipated foundation loads. These estimated ultimate settlements are calculated to be a maximum of 1 inch when using the recommended bearing values. As a practical matter, differential settlements between footings can be assumed as one- half of the total settlement. These elastic settlements are expected to occur during construction. Resistance to lateral loads may 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 0.40 between soil and concrete may be used for dead load forces only. A passive earth pressure of 250 pounds per square foot, per foot of depth, may be used along the sides of footings that are placed against properly compacted native or approved import soil. Retaining walls may be required to accomplish the proposed construction. Cantilever retaining walls may be designed using "active" pressures. Active pressures may be estimated using an equivalent fluid weight of 40 pcf for native backfill soil with level free-draining backfill conditions. For walls that are restrained, "at rest" pressures should be utilized in design. At rest pressures may be estimated using an equivalent fluid weight of 60 pcf. Walls should be provided with adequate drainage. It is our opinion that the remedial grading recommended in the referenced report remains appropriate. The remedial grading necessary at this time should include overexcavation of the surface soil throughout the proposed building areas. The building pad areas should be cleared of any surface vegetation prior to grading. In order to provide for firm and uniform foundation support, we recommend overexcavation and recompaction. The building areas should be overexcavated to a depth of at least 3 feet below existing grade or 3 feet below pad grade, whichever is deeper. The exposed surface should then be scarified, moisture conditioned and compacted to a minimum of 90 percent relative compaction. The previously removed soil and fill material may then be placed in thin lifts and compacted to at least 90 percent relative compaction. It should be noted that the site is located within a seismically active area of Southern California and it is likely that the proposed structures will experience strong ground shaking as a result of an earthquake event along one of the faults in the region during the expected life of the development. As a minimum, structures should be designed based upon Seismic Zone 4 design criteria included in the 2007 California Building Code (UBC). The potential for liquefaction or other geologic/seismic hazards occurring at the site is considered to be negligible. Sladden Engineering S I August 29, 2008 -3- Project No. 444-3161 08-08-467 Based on our field observations and understanding of local geologic conditions, the soil profile type judged applicable to this site is SD, generally described as stiff soil. The site is located within UBC Seismic Zone 4. The following presents additional coefficients and factors relevant to seismic mitigation for new construction upon adoption of the 2007 California Building Code (CBC). 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 ½ second. This assumption should be verified by the project structural engineer. The 2007 CBC Seismic Design Parameters are summarized on the following page. Occupancy Category (Table 1604.5): II Site Class (Table 1613.5.5): D Ss (Figure 1613.5.1):1.183g Si (Figure 1613.5.1): 0.445g Fa (Table 1613.5.3(1)): 1.0 Fv (Table 1613.5.3(2)): 1.5 Sms (Equation 16-37 (Fa X Ssfl: 1.215g Smi (Equation 16-38 {Fv X Si)): 0.692g SDs (Equation 16-39 {2/3 X Sms}): 0.810g SD1 (Equation 16-40 12/3 X Srni}): 0.461g Seismic Design Category based on SDs (Table 1613.5.6(1)): D Seismic Design Category based on SD1 (Table 1613.5.6(2)): D We appreciate the opportunity to provide service to you on this project, if you have any questions regarding this letter or the referenced reports please contact the undersigned. Respectfully submitted, SLADDEN ENGINEERING ESSi5" NOp( II( Brett L. 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