Loading...
HomeMy WebLinkAboutCT 02-28; La Costa Condominiums; Second Responses to Third Party Review; 2008-05-13American Geotechnical, Inc. SOIL, FOUNDATION AND GEOLOGIC STUDIES May 13, 2008 File No. 23280.01 Mr. Frank Jimeno, P.E. CITY OF CARLSBAD PUBLIC WORKS - ENGINEERING DIVISION 1635 Faraday Avenue Carlsbad, California 92008 Subject: SECOND RESPONSES TO THE THIRD PARTY REVIEW PROPOSED LA COSTA CONDOMINIUMS, LOT 185 La Costa Avenue South - Unit 1 Carlsbad Tract No. 02-28 Carlsbad, California Reference: "First Review of Responses to Third-Party Review of Geotechnical Reports, Proposed La Costa Condominiums, Carlsbad, California", prepared by Testing Engineers - San Diego, Inc., dated April 9, 2008. "Revised Update Geotechnical Report, Proposed La Costa Condominiums, Lot 185, La Costa Avenue South - Unit 1, Carlsbad Tract No. 02-28, Carlsbad, California", prepared by American Geotechnical, dated February 14, 2008. Dear Mr. Jimeno: American Geotechnical is pleased to present the second phase of responses to the Third-Party Review referenced above. We appreciate the opportunity to be of service. If you should have any questions, please do not hesitate to contact us. Sincerely, AMERICAN GEOTECHNICAL Edred T. Marsh Principal Engineer G.E.2387 ETM: kb Distribution: Mr. Frank Jimeno, P.E. - (2)Via Mail Only 22725 Old Canal Road, Yorba Linda, CA 92887 - (714) 685-3900 - FAX (714) 685-3909 5764 Pacific Center Blvd., Suite 112, San Diego, CA 92121 (858) 450-4040 - FAX (858) 457-0814 712 Fifth Street, Suite B, Davis, CA 95616 - (530) 758-2088 - FAX (530) 758-3288 5600 Spring Mountain Road, Suite 201, Las Vegas, NV 89146 - (702) 562-5046 - FAX (702) 562-2457 HAmerican Geotechnical, Inc. File No. 23280.01 May 13,2008 Page 1 RESPONSES I. The geologic contacts have been corrected and are depicted on the attached plates. 6. We agree that the Benton As-Graded reports were not reviewed. 9. The fill material was investigated by Leighton & Associates. We believe that the laboratory test data provided in the Leighton report supports that the deeper fill has a low potential for settlement. Recommendations for treatment of other fill areas are given in Sections 6.2.3 and 6.2.4 of the referenced report. All existing fill material located within the sheet-graded building pads should be removed and replaced with properly compacted fill to a minimum depth of five feet below proposed finish grade. 10. There are no present "active" landslides and only one "recent" landslide. The recent landslide is located along cross-section C-C' (attached) and is currently being repaired. I1. The shear strength parameters used in the analysis were obtained from both Leighton & Associates test results and test results performed by American Geotechnical. One residual direct shear test was performed that was obtained from the recent landslide. That was not included in the referenced report. We have included the test results as an attachment. 17. The queried surfaces have been removed from the cross-section (attached) 19. We believe the fill will not be undermined. This condition will be confirmed during grading. 22. The origin of the three samples were as follows: One clay sample from the large flat pad, one sandy sample from the recent slope failure and one sample was a mixture of the two. 25. All colluvium will be removed during remedial grading and replaced with compacted fill keyed and benched into the natural slope. 26. The limits of the proposed buttress have been shown on the attached cross-section L-L'. Only shallow removals are anticipated above the proposed buttress. 29. The off-site fill slopes will have some improvement including drainage being directed to new "V" ditches via tightlines instead of emptying directly over the slopes. 33. The sub-drains are being reflected by notes on the plans prepared by O'Day Consultants. HAmerican Geotechnical, Inc. File No. 23280.01 May 13, 2008 Page 2 34. The detail for the Detention Basin liner will be included on the plans prepared by O'Day Consultants. 39. Updated recommendations for foundations on expansive soils will be provided once grading is completed. For preliminary design purposes the following parameters can be used: MODERATE EXPANSION: Edge Lift: em= 5.0 feet, ym= 1.0 inch Center Lift: em= 5.0 feet, ym= 2.5 inches HIGH EXPANSION: Edge Lift: em= 5.0 feet, ym= 2.0 inches Center Lift: em= 5.0 feet, ym= 3.5 inches For both conditions it is recommended that the upper 2 feet of soil be pre-soaked to 1.5 times optimum moisture content. 48. The term "aerial" refers to a birds eye view of the building foot print. The limits should extend 5 feet "outside" of or "beyond" the proposed foundations. GENERAL COMMENT Based on our recent discussion the remedial "slot" grading planned for landslide removal will be increased from 3 slots to 6 slots (doubled) and currently a repair is being performed to remediate a recent landslide along cross-section C-C'. It is expected that additional information will be learned from the removals and re- grading in this area.