The URL can be used to link to this page

Home My WebLink AboutCT 13-04; GOLDEN SURF; GEOTECHNICAL RESPONSE TO CITY OF CARLSBAD ENGINEERING DEPARTMENT COMMENTS; PUD 13-10, CDP 13-33; 2014-07-25SEP 1 2 2014 ,... ..... . Geotechnical • Geologic • Coastal • Environmental 5741 PalmerWay • Carlsbad, California 92010 • (760)438-3155 • FAX (760) 931-0915 • www,geosoilsinc.com July 25, 2014 W.O. 6309-A4-SC Golden Surf Holdings, Ltd 6798 Paseo Del Norte Carlsbad, California 92009 Attention: Mr. Farzan Demoubed Subject: 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 geotechnical response to December 6, 2013 plan check comments prepared by the City of Carlsbad Engineering Department (City of Carlsbad, 2013 [see the Appendix]). The services GSI performed for this study included a review of the referenced documents (Appendix), analysis of data, and the preparation ofthis response letter. Unless specifically superseded herein, the conclusions and recommendations contained in the project geotechnical report listed in the Appendix, are still considered valid and applicable, and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 (2013) Based on our review of City of Carlsbad (2013), GSI understand that we are required to respond to the geotechnical aspects of Engineering Department plan check Comments 1, 4, and 6. These plan check comments are repeated below in italic font, followed by GSI's response. City of Carlsbad Engineerinq Department Plan Check Comment No. 1 In order for the proposed development to be found subject to standard and not priority stormwater requirements, the private driveways are proposed to be constructed ofpen/ious pavers over permeable base. The on-site soil type is identified as Type D on the tentative map (low permeability). The preliminary geotechnical evaluation by GeoSoils dated November 30, 2011 states on page 41 that water should not be allowed to seep into the ground. Section E on page C-3 would seem to indicate that runoff collected in the permeable base would sheet flow over the flush curb prior to infiltration into the subgrade. Address these apparent conflicting issues in the preliminary geotechnical investigation. Include a discussion companng the storage volume of the permeable base below the top ofthe adjacent flush curb (considering the 3% driveway cross slope) and the infiltration rate of the subgrade material to the 100 year storm runoff volume. Consider the 3% cross slope and the 3% longitudinal slope of the driveway in the discussion. GSI Response to City of Carlsbad Engineerinq Department Plan Check Comment No. 1 The design of Low Impact Development Best Management Practices typically falls under the purview of the project civil engineer and/or designer. Therefore, it is our opinion that Spear and Associates, Inc., should respond to this issue. Infiltration within the influence of settlement-sensitive improvements (i.e., below a 1:1 [horizontal:vertical]) projection down from the settlement-sensitive improvements), will increase the potential for distress. However, if stormwater infiltration into the private driveway subgrade is necessary to comply with local. State, and Federal requirements, GSI recommends that Tencate/Mirafi HP570 geotextile be placed between the subgrade and the permeable base layer to reduce the potential for deformations of the saturated driveway subgrade to reflect at the surface. Concrete cut-off walls should also be provided along the perimeter ofthe private driveway where settlement-sensitive improvements are located adjacent to the driveway. The cut-off walls should be a minimum of 6 inches wide and should extend at least 12 inches below the driveway subgrade. It is our opinion that this mitigation would reduce the potential for distress, but not entirely eliminate it. Therefore, the developer should anticipate the need for increased maintenance/repair, or premature replacement of improvements located above and adjacent to areas where infiltration is planned. The potential for distress, increased maintenance/repair, or replacement should be disclosed to all interested/affected parties. Citv of Carlsbad Enq/neer/ng Department Plan Check Comment No. 4 Page 42 of the preliminary geotechnical evaluation states that downspouts if utilized should be drained into PVC collector pipes. Development projects are required to implement low impact design (LID) features. To meet this requirement, downspouts should discharge to vegetated swales. Please address this requirement in the preliminary geotechnical investigation. GSI Response to City of Carlsbad Engineering Department Plan Check Comment No. 4 Unlined infiltrations systems, including vegetated swales, should not be installed within ±8 feet of building foundations, underground utility trenches, walls, and other settlement- sensitive improvements, and/or a below 1:1 (h:v) projection (down and away) from the bottom, outside edges of these improvements. Alternatively, deepened foundations and/or Golden Surf Holdings, Ltd. W.O. 6309-A4-SC Parcel 1 of Parcel Map 6136, Carlsbad . July 25, 2014 File: e\wp12\6300\6309a4.grt GCOSoilS, IllC. Page 2 pile/pier supported improvements may be used where unlined infiltration systems are located within aforementioned zones from the proposed improvements. As another alternative, the use of lined bio-swales may also be considered. Impermeable liners for onsite stormwater treatment should consist of a 30-mil polyvinyl chloride (PVC) membrane that meets the following minimum specifications: Specific Gravity (ASTM D792): 120 (min.); Tensile (ASTM D882): 73 (Ib/in-width, min); Elongation at Break (ASTM D882: 380 (%min); Modulus (STM D882): 30 (Ib/in-width, min.); and Tear Resistance (ASTM D1004): 30 (lb/in, min). It is our opinion that roof gutter downspouts may discharge into lined bio-swales provided that the bottom of the swale is located above a 1:1 (horizontal:vertical) projection down from the bottom outside edge of any onsite or offsite settlement-sensitive improvements. Citv of Carlsbad Eng/neer/nq Department Plan Check Comment No. 6 Proposed retaining walls around the project perimeter are shown to be constructed within 0.08' of the property line. Please include a discussion in the preliminary geotechnical investigation of the proposed method of construction to insure cut slope stability from the top of the adjacent property to the bottom of the key trench. GSI Response to City of Carlsbad Engineering Department Plan Check Comment No. 6 GSI respectfully points out that the only area of the project where the condition described by the reviewer occurs is along portions of the westerly and southwesterly project boundaries. Other walls are shown to retain the project. In order to provide for cut slope stability, the developer may elect to construct the walls in alternating slot excavations or incorporate the use of shoring. Alternatively, the developer may obtain an agreement from the adjacent property owner to grade offsite and then restore the disturbed areas to their original condition following the backfill of the retaining walls. Another alternative would be to relocate these walls such that the temporary slope gradients recommended in GSI (2011) are maintained. LIMITATIONS The conclusions and recommendations are professional opinions. These opinions have been derived in accordance with current standards of practice, and no warranty, either express or implied, is given. Standards of practice are subject to change with time. GSI assumes no responsibility or liability for work or testing performed by others, or their inaction; or work performed when GSI is not requested to be onsite, to evaluate if our recommendations have been properly implemented. Use of this report constitutes an agreement and consent by the user to all the limitations outlined above, notwithstanding Golden Surf Holdings, Ltd. W.O. 6309-A4-SC Parcel 1 of Parcel Map 6136, Carlsbad ^ July 25,2014 File: e\wp12\6300\6309a4.grt GCOSoUS, ItlC. Page 3 any other agreements that may be in place. In addition, this report may be subject to review by the controlling authorities. Thus, this report brings to completion our scope of services for this portion of the project. 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 Ryan B. Boehmer Project Geologist RBB/JPF/DWS/jh Attachment: Appendix - References David W. Civil Engineer, RCE 47857 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 (via email) Golden Surf Holdings, Ltd. Parcel 1 of Parcel Map 6136, Carlsbad File: e\wp12\6300\6309a4.grt GeoSoils, Inc. W.O. 6309-A4-SC July 25, 2014 Page 4 APPENDIX REFERENCES City of Carlsbad Community and Economic Development, 2013, 1^' review for CT 13-04/PUD 13-10/CDP 13-33 - Golden Surf, dated December 6 GeoSoils, Inc., 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. mp is-fu Pim la-in mP la-aa i z o 3 liJ Q I It: DRAINAGE AREA DMA BREAKDOWN amtXMEU SURFXE SrUBOL SM. TYK DRMHMXAKA 'A' BUILDING ROOFTOP TYPE B 8,965 SO FT H4fiSCAPING/SIDEWALJ( TYPE B 918 SQ FT PARKING/DRIVE AISl£ (paimjs PAVERS) TYPE B 7,698 SO FT