The URL can be used to link to this page

Home My WebLink AboutCDP 2020-0026; BEGONIA COURT RETAINING WALL; GEOTECHNICAL ADDENDUM; 2020-09-10/JOVPN:,ED GEOTECHI\ICAL SOLlJTlONS, INC. 485 Corporate Drive, Suite B Escondido, Ca 92029 Telephone: (619) 867-0487 FUSION ENGINEERING & TECHNOLOGY 423 I Balboa Avenue, Suite 619 RFCE.-VED SEP 11 2020 CITY Of-\JARLSBAD September I 0, 2020 P/W 1907-03 Report No. 1907-03-8-4 San Diego, CA 921 I 7 Attention: John Rivera, PE PLANl'-JII\JG DIVISIO'.'-J Subject: Geotechnical Addendum, Response to City of Carlsbad Engineering Review Comments, Lichtman Residence, 939 Begonia Court, City of Carlsbad, California. References: Appendix Gentlemen: In accordance with your request and authorization, Advanced Geotechnical Solutions, Inc., has prepared this response to Engineering Review Comments provided by the City of Carlsbad Community Development Department regarding the existing Mechanically Stabilized Earth (MS£) retaining walls in the rear yard of the Lichtman Residence located at 939 Begonia Court, City of Carlsbad, California. More specifically, this letter has been prepared in response to Engineering review comments 1 a through I g from the I st Review for CDP 2020-0026N 2020-0004 (DEV 2020-0134) -Begonia Court Retaining Wall dated June 29, 2020 and provided to AGS on September 9, 2020. Unless superseded in the text of this addendum report, the conclusions and recommendations presented in referenced geotechnical report (AGS 2019) remain valid and applicable and should be properly implemented. In preparing this response to cycle review comments we have first presented the review comment followed by our response. City of Carlsbad-Submit supplemental geolechnical report to the report dated October 9, 20 I 9 by A GS expanding on analysis and recommendations of the third option chosen to reinforce the existing system. Include in the supplemental geotechnical report: la -Recommendations for anchor locations, lengths, spacing, etc. and specify which walls shall be anchored. AGS Response -It is our understanding that stabilization of the existing MSE retaining walls will be performed on a design-build basis. The design-build contractor will provide the locations, lengths, spacing, etc. of the soil nails/tie-backs and determine which walls will be anchored. Any MSE retaining walls not stabilized with a shotcrete and soil nail/tie-back system should be evaluated by AGS and may require reconstruction using the appropriate geogrid type, length, and spacing and the reinforced and retained soils compacted to a minimum of90 percent of the dry density per ASTM D- 1557. The shotcrete with soil nail/tie-back system should be designed by a licensed engineer familiar with these systems. The soil nail/tie-back capacity is dependent on the drilling and grouting methods and should be estimated by the design-build contractor. Testing should be conducted during construction. For preliminary estimating purposes, ultimate anchor capacities in the formational materials (sandstone) can be assumed to be 4,300 pounds per square foot (30 psi). Since the above friction capacities are considered ultimate, an appropriate factor of safety should be incorporated into the design. Soils nails should be embedded a minimum of IO feet into competent formational ORANGE AND L.A. COUNTIES (714) 786-5661 INLAND EMPIRE (619) 708-1649 SAN DIEGO AND IMPERJAL COUNTIES (6 19) 867-0487 1 Page 2 Report 1907-03-8-4 September I 0, 2020 P/W 1907-03 materials. The soil nail/tie-back reinforcement system should be designed to support an active pressure corresponding to an equivalent fluid weight of 40 pcf for level backfill and 60 pcf for sloping backfill, and should also consider the surcharges of the tiered walls. When a design is available, it should be reviewed by AGS and a global stability analysis performed. 1 b -Installation methods and procedures. AGS Response -Installation methods and procedures should be provided by the design-build contractor. Typically, this type of reinforcement may first include coring through the MSE wall blocks at predetermined locations. Hand drills would be used to advance an inclined hole to the des ign length. The soil nail would be placed in the hole and possibly tubes for primary and post grouting. Testing of selected soil nails would be completed after grouting. Drain boards may be installed on the outside of the MSE wall blocks and a reinforcement mat may be installed. Bearing plates would be affixed to the end of the nails and poss ibly tied to the reinforcement mat on the outside of the MSE wall. Shotcrete would then be applied to complete the wall. 1 c -Assess overall feasibility of the project. AGS Response -Stabilization of the existing MSE retaining wall system with soil nails/tie-back anchors is considered feasible from a geotechnical perspective. Plans for the stabilization of the existing retaining walls should be reviewed by AGS when they are available. 1 d -Location Map. AGS Response -Figure I-Site Location Plan is included herewith. 1 e -Describe impacts on adjacent properties/improvements as a result of site grading and construction. AGS Response -It is anticipated that the impacts on adjacent properties/improvements as a result of site grading and construction will be negligible to favorable. It should be noted that depending on the final design length of the soil nails/tie-backs, they may encroach into the superjacent parcel(s) and require permission from the adjacent property owner(s). lf -Reference applicable building/grading codes/ordinances. AGS Response -Applicable building/grading codes/ordinances should be provided by the design engineer and included on the project plans. 1 e -Recompaction requirements as the fill has not been recompacted to a minimum of 90% of relative compaction per the conclusions in Section 6. 0 of October 9, 2019 report. Is recompaction of slopes and level areas between wall required for this remediation option? Design engineer shall also estimate remediation quantities for recompaction in their grading quantity assessment. AGS Response -AGS is unaware of slopes between walls with the exception of the stairs. Provided that there are no structural or settlement sensitive improvements constructed in the project area and that some settlement of the retained soils is acceptable to the property owner, recompaction of the existing retained fill soils is not required. The recommended design active pressure for the ADVANCED GEOTECHNICAL SOLUTIONS, INC. Page 3 Report 1907-03-8-4 September I 0, 2020 P/W 1907-03 reinforcement system and the shear strengths provided in the referenced report that should be used for the global stability analysis have considered the current condition of the existing fill. Advanced Geotechnical Solutions, Inc. appreciates the opportunity to provide you with geotechnical consulting services and professional opinions. Should you have any questions, please contact the undersigned at (61 9) 867-0487. Respectfully Submitted, Advanced Geotechnical Solutions, Inc. Distribution: Anachments: VAN E 2790, Reg. Exp. 6-30 (3) Addressee References Figure I -Site Location Map PAUL J. DERJSI CEG 2536, Reg. Exp. 5-3 I ADVANCED GEOTECHNICAL SOLUTIONS, INC. 1 Page 4 Report 1907-03-8-4 REFERENCES September I 0, 2020 P/W 1907-03 Advanced Geotechnical Solutions, Inc. (20 I 0). "Geotechnical Evaluation of Existing Mechanically Stabilized Earth Walls, 939 Begonia Court, City of Carlsbad, California," dated October 9, 2019, Report No. 1907-03-8-3. Fusion Engineering and Technology, Preliminary Site Plan for Lichtman Residence, 939 Begonia Court, City of Carlsbad, California, Map I of I, I 0-Scale, undated. Kennedy, M.P., and Tan, S.S., 2007, Geologic Map of the Oceanside 30' x 60' Quadrangle, Cali fornia Geological Survey: Scale 1: 100,000. ADVANCED GEOTECHNICAL SOLUTIONS, INC. N i SCALE 1:48000 33 SITE LOCATION MAP 939 BEGONIA COURT, CARLSBAD, CALIFORNIA P/W 1907-03 Batiquitos Lagoon FIGURE 1 SOURCE MAP-U.S.G.S. TOPOGRAPHIC MAP OF THE ENCINITAS 7.5 MINUTE QUADRANGLE, ~~Gs ADVANCED GEOTECHJ'<ICA.L SOLUTIONS, INC. 485 Corporate Drive, Suite B Escondido, CA 92029 SAN DIEGO COUNTY, CALIFORNIA (2018) Telephone: (619) 867-0487 Fax: (714) 409-3287