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Home My WebLink AboutCT 02-28; LA COSTA CONDOMINIUMS; LANDSIDE STABILIZATION; 2008-04-29American GeotechnicaUnc SOIL, FOUNDATION AND GEOLOGIC STUDIES April 29, 2008 File No. 23080-01R City of Carlsbad - Public Works 1635 Faraday Avenue Carlsbad, CA 92008 Attention: Mr. Steve Bobbett Subject: RESPONSE TO THIRD-PARTY REVIEW LANDSLIDE STABILIZATION Banich, Powers, and Calso Landslide Carlsbad, California Reference: THIRD-PARTY REVIEW OF CONSTRUCTION REVISION By: Bureau Veritas North America, Inc. Dated: Apirl 9, 2008 Dear Mr. Bobbett: We are in receipt ofthe third-party review ofthe landslide stabilization forthe Banich, Powers, and Calso Landslide, Carlsbad, California. In Appendix A, we have reproduced the third-party review by Bureau Veritas North America, Inc. In response to their comment, we have reproduced our gross slope stability analyses in Appendix B. This gross slope stability analyses is reproduced from Appendix C of our report dated March 27, 2007. As our gross slope stability analyses shows, we assumed that the upper part of the slope would be re- built to approximately pre-failure conditions. We utilized an upper slope inclination of 37 degrees, which is essentially a 1.3:1.0 (horizontahvertical) slope ratio. Please also note that the gross slope stability analyses indicates a factor of safety of 1.612 (Bishop Method) and this factor of safety does not include the stabilizing effect ofthe three, upper tie back walls and the proposed geogrid in the upper part of the slope. Hence, we have used a conservative gross slope stability analyses by not including the stabilizing effect of the upper tie back walls and the presence of geogrid, and yet the gross factor of safety is still in excess of 1.5. Thus, it is our opinion that the final constructed condition ofthe re-built slope, which includes the tieback walls and geogrid, will have a gross factor of safety in excess of 1.5. 22725 Old Canal Road, Yorba Linda, CA 92887 • (714) 685-3900 • FAX (714) 685-3909 5600 Spring Mountain Road, Suite 201, Las Vegas, NV 89146 • (702) 562-5046 • FAX (702) 562-2457 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 File No. 23080-01R April 29, 2008 Page 2 liAmerican Geotechnical, Inc. We appreciate the opportunity to be of service. If you should have any questions or concerns, please do not hesitate to contact our office. Respectfully submitted, AMERICAN GEOTECHNICAL, INC. igory/W. Axten PTssident/CEO G.E. 103 GWA: dd Enclosures: Appendix A - Third Party Review Appendix B - Gross Slope Stability Analyses Distribution: 3 - Mr. John Strohminger (Overnight) O'Day Consultants, 2710 Loker Ave. West, Carlsbad, CA 92010 1 - Mr. Bob Day (Regular Mail & Email: davb@amqt.com) American Geotechnical, Inc. wpdata/20000/23080-01R.gwa,dd.april.2008.ResponsetoThird-PartyReview File No. 23080-01R liAnTierican Geotechnical, Inc. April 29, 2008 APPENDIX A Third Party Review Apr-18-2008 14:38 Froni-O'DAY CONSULTANTS 7609318680 T-986 P.002/003 F-777 BUREAU VERITAS April 9, 2008 Contract No.: 148589 Mr. Steve Bobbett City cf Carlsbad-Publio Works 1635 Faraday Avenue Carlsbad, CA 92008 Subject: Third-Party Review of Construction Revision Landslide Stabilization Banich, Powers, Calso Landslide 2416 Sacada Circle Carisbad, California Dear Mr. Bobbett: introduction As requested, Bureau Veritas North America, Inc. has perfomned a third-party geotechnical review of the constmction revision for the subject project. The purpose of our review was to provide an opinion on whether the geotechnical aspects of the construction revision have been identified and appropriately addressed In the project geotechnical documents. This letter presents the results of our third-party review. Our review is based on geotechnical data presented in the project geotechnical documents and our professional judgment. We have not performed a subsurface investigation, laboratory testing or Independent geotechnical analysis for the project. The following project documents were provided for our review: 1. "Interim Repair Recommendations, Landslide Stabilization, Banich, Powers, Calso Landslides, 2416 Sacada Circle, Carisbad, Califomia," prepared by American Geotechnical, Inc., File No. 23080-02, dated February 19,2008. 2. "Landslide Stabilization Recommendations, Banich Powers, Calso Landslides, 2416 Sacada Circle, Carisbad, Califomia 92009," prepared by American Geotechnical, Inc., File No. 23080.02, dated March 27 2007. 3. "Project Plans for Banich, Powers, Calso Landslide Stabilization," Sheets 1 to 6, prepared by American Geotechnical, inc., dated March 27,2007. Testing Engineers San Diego A Bvrmw Veritas Company ^^^^.^ gjg 7,5 jg^Q 7R95 Convoy Court. Suite 18 Pa^,. 7,3 55, Q ^tin Oi^ec CA 92111 w>^w.uS.burvauyeriu«.com Apr-18-2008 14:39 Froni-O'DAY CONSULTANTS 7609318680 CHy of Cartebad Banich, Powers, Calso Landslide T-986 P.003/003 F-777 Contract No.: 148569 Results of Review Based on our geotechnical engineering review it is our opinion that the following comment should be addressed by the project geotechnical engineer of record: 1. In reviewing Interim Repair Recommendations (see reference no. 1), American Geotechnical, Inc. states in the third paragraph of Issue No 2 that "In terms of gross stability, the factor of safety Is unchanged for the upper part of the slope due to the support provided by the three tieback walls and additional soil reinforcement." Since the slope ratio will change from 1 51 (horizontal to vertical) to 1.2:1, It Is unlikely that the factor of safety for the gross slope stability will remain unchanged. In any case, the geotechnical engineer of record should provide global slope stability analyses showing that the factor of safety is greater than 1.5 and 1.1 for the static and seismic conditions, respectively. The opportunity to be of service on this project is appreciated. If you have any questions regarding our review, please contact our office. Respectfully submitted, Testing Engineers - San Diego, Inc. A Bureau Veritas Company Nick Tracy, EIT Staff Engineer ^an Olin, PE, GE Principal Geotechnica lene CiKttenborder, CEG Senior Engineering Geologist NT/GCA/0:cs Distribution: (4) Addressee File No. 23080-01R April 29, 2008 liAmerican Geotechnical, Inc. APPENDIX 8 Gross Slope Stability Analyses 150 — 120 — 90 - Description: Banich Comments: Slide Removal with Buttress and groundwater contr File Name: Banich - 4.slp Last Saved Date: 9/21/06 Last Saved Time: 12:40:18 PM Analysis Method: Bishop Direction of Slip Movement: Right to LeJ Slip Surface Option: Grid and Radiuj P.W.P. Option: Piezometric Line^^u Soil; 1 Description: Fill Soil Model: Mohr-CoulomJ Unit Weight: 125 Cohesion; 250 Gescnption. Sandst^e Phi- 33 ^^'^^i Mchr-Coulomb Unit Weight: 125 Cohesion: 1000 Phf- 40 - 150 i = 60 (D r Soil: 3 Description: Buttress Soil Model: Mohr-Coulomb Unit Weight; 125 Cohesion: 100 Phi: 33 30 'rr- Horizontal Scale (feet)