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HomeMy WebLinkAboutCT 13-04; Golden Surf; Tentative Map (CT)Geotechnical • Geologic • Coastal • Environmental 5741 Pal,,.„, .".ay • Carlsbad, California 92010 • (760)438-3155 • FAX (760) 931-0915 • www.geosoilsinc.com Revised December 10, 2014 W.O. 6309-A5-SC Golden Surf Holdings, Ltd 6798 Paseo Del Norte Carlsbad, California 92009 Attention: Mr. Farzan Demoubed Subject: Addendum and Geotechnical Response to City of Carlsbad Engineering Department Plan Check Comments, Parcel 1, Parcel Map 6136, 1000 Camino De Las Ondas, Carlsbad, San Diego County, California, CT 13-04, PUD 13-10, and CDP 13-33 Dear Mr. Demoubed: In accordance with your request and authorization, GeoSoils, Inc. (GSI) is providing this addendum and geotechnical response to October 27, 2014 plan check comments prepared by the City of Carlsbad Engineering Department (City of Carlsbad, 2014 [see the Appendix]). The sen/ices GSI performed for this study included a review of the referenced documents (Appendix), analysis of data, and the preparation of this addendum and response letter. Unless specifically superseded herein, the conclusions and recommendations contained in the project geotechnical reports listed in the Appendix, are still considered valid and applicable, and should be appropriately implemented during project design and construction. RESPONSE TO CITY OF CARLSBAD (2014) Based on our review of City of Carlsbad (2014), GSI understands that we are required to respond to the geotechnical aspects of Engineering Department Comment No. 3. This plan check comment is repeated below in /fa//c font, followed by GSI's response. Citv of Carlsbad Eng/neer/nq Department Plan Check Commenf No. 3 Based on GSI's response to first review comment #6, provide an addendum from the geotechnical consultant indicating the project's technical ability to be constructed as proposed. GSI Response to City of Carisbad Engineering Department Plan Check Comment No. 3 Based on our review of Spear and Associates (2014) and GSI (2011 and 2014), it is our opinion that the project is feasible from a geotechnical perspective. The most significant geotechnical issues with the proposed residential development shown on Spear and Associates (2014) are: 1) the potentially compressible nature of the near-surface soils (i.e., overburden soils); 2) expansive near-surface soil conditions within the northerly quadrant ofthe project; 3) the potential for corrosion to exposed buried metals if left in direct contact with the onsite soils; 4) limitations to remedial grading and support of planned improvements near property lines due to boundary/perimeter conditions; and 5) retaining wall construction along portions ofthe westerly and southwesterly project boundaries. GSI points out that remedial earthwork recommendations for the treatment of the potentially compressible soils were previously provided in GSI (2011). In addition, in GSI (2011), we provided recommendations for the design and construction of post-tension and mat foundation systems to mitigate the expansive onsite soils. As an alternative to the use of structural mitigation for expansive soils, the developer may elect to remove expansive soils from the site, and replace those soils with non-detrimental ly expansive soils (i.e., soils with an expansion index less than 21 and a plasticity index less than 15), or place them outside the influence of the residential structures. However, the latter could affect the long-term performance of any ancillary site improvement (i.e., walls, hardscape, pavements, etc.) constructed above or near expansive soils. We note that recommendations for walls and flatwork in consideration of expansive soils, are provided in GSI (2011). Recommendations to mitigate the corrosive effects ofthe onsite soils are also provided in GSI (2011). The project is bounded by private property on its westerly, easterly, and northerly sides, and by City of Carlsbad property (i.e., Camino De Las Ondas) on its southerly side. On page 17 of GSI (2011), we recommended that the removal and recompaction of potentially compressible soils be completed below a 1:1 (hohzontakvertical [h:v])projection down from the bottom outboard edge of any planned settlement-sensitive improvement and/or limits of new planned fills. Given the boundary conditions, it appears that remedial grading will be limited at the property lines. Thus, the developer should consider the use of deepened foundations for the support of the planned perimeter retaining walls. Geogrid, soil cement, and/or structural mitigation may be used for other settlement-sensitive improvements (i.e, hardscape and pavements) constructed abovea 1:1 (h:v) plane upfrom the bottom outboard edge ofthe remedial grading excavation. Alternatively, the developer may elect to not perform any mitigation within this zone. Should this be the case, the potential for settlement and associated distress, and a reduced serviceable life of improvements constructed within this zone cannot be precluded. Planned retaining wall construction along the westerly and southwesterly property lines appears to require temporary slopes that will exceed the recommendations provided on page 18 of GSI (2011), without the implementation of offsite grading. General recommendations, including the use of shoring structures, constructing the walls in Golden Surf Holdings, Ltd. W.O. 630g-A5-SC Parcel 1 of Parcel Map 6136, Carlsbad , Revised December 10, 2014 File: e\wp12\6300\6309a5.rgrt GCOSoilS, IlIC. Page 2 alternating slot excavations, or relocating these walls were provided in GSI (2014). The developer may perform a value engineering study centered on quality, speed of construction, and cost, prior to the selection ofthe engineered solution. Based on limited space, gravel backfill wrapped in filter fabric may be necessary behind these particular walls. In summary, recommendations have been provided by GSI for the project to be constructed as proposed, from a geotechnical viewpoint. If you have any questions or comments regarding this letter, please do not hesitate to contact the undersigned. Respectfully submitted, GeoSoils, Inc. 'John P. Franklin Engineering Geologist, CEG 1340 nowiH \A/ i David W Civil Engineer, yan B. Boehmer Project Geologist RBB/JPF/DWS/jh Attachment: Appendix - References Distribution: (2) Addressee (via email and US mail) (1) Spear and Associates, Inc., Attention: Mr. Josh Ziegler (via email) (1) Karnak Planning and Design, Attention: Mr. Robert Richardson (viaemail) Golden Surf Holdings, Ltd. Parcel 1 of Parcel Map 6136, Carlsbad File: e\wp12\6300\6309a5.rgrt GeoSoils, Inc. W.O. 6309-A5-SC Revised December 10, 2014 Page 3 APPENDIX REFERENCES City of Carlsbad Community and Economic Development, 2014, 2"" review for CT 13-04/PUD 13-10/CDP 13-33 - Golden Surf, dated October 27. GeoSoils, Inc., 2014, Geotechnical response to City of Carlsbad Engineering Department plan check comments. Parcel 1, Parcel Map 6136, 1000 Camino De Las Ondas, Carlsbad, San Diego County, California, CT 13-04, PUD 13-10, and CDP 13-33, W.O. 6309-A4-SC, dated July 25. , 2011, Preliminary geotechnical evaluation, Paseo Point Minor Subdivision, 6798 Paseo Del Norte, City of Carlsbad, San Diego County, California, W.O. 6309-A-SC, dated November 30. Spear and Associates, Inc., 2014, Conceptual grading plans for: Parcel 1, P.M. 6136, 1000 Camino De Las Ondas, Sheets 2 and 3 of 3, Drawing Nos, C-2 and C-3, 20-scale, dated July 10. GeoSoils, Inc.