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Home My WebLink AboutPD 2022-0024; 2780 JAMES DRIVE; GEOTECHNICAL RESPONSE TO COMMENTS; 2023-01-23Geotechnical C Geologic C Coastal C Environmental 5741 Palmer Way C Carlsbad, California 92010 C (760) 438-3155 C FAX (760) 931-0915 C www.geosoilsinc.com January 23, 2023 W.O. 8320-A1-SC A.C. Mattos, Inc. 3276 Highland Drive Carlsbad, California 92008 Attention:Ms. Ana Mattos Subject:Response to City of Carlsbad Review Comments, 2780 James Drive, Carlsbad, California 92008, Project Issues Report PRJ-1048739 References:1. “Geotechnical Evaluation, Proposed Single-Family Residential Development, 2780 James Drive. Carlsbad, San Diego County, California,” W.O. 8320-A, dated June 6, 2022, by GeoSoils, Inc. 2. “Geotechnical Report Review, Single-Family Residence, 2780 James Drive, Project ID PD 2022-0024, Grading Permit No. GR2022-0039,” dated October 5, 2022, by the City of Carlsbad Land Development Engineering. Dear Ms. Mattos: In accordance with your request, GeoSoils, Inc. (GSI) is providing this response to City of Carlsbad comments. The scope of our services has included a review of the referenced report (Reference 1), analysis of data, and preparation of this response. Unless specifically superceded herein, the conclusions and recommendations contained in the referenced report by GSI (see Reference No. 1) remain pertinent and applicable, and should be appropriately implemented during planning, design, and construction. GSI REVIEW RESPONSE For convenience, the reviewer’s comments are repeated below in italics, followed by GSI’s response. Comment Comment No. 1: Please review the most current grading plan for the project and provide any additional geotechnical recommendations or modifications to the geotechnical report as necessary. GeoSoils, Inc. Response to Comment No. 1: Acknowledged. No additional geotechnical recommendations or modifications are deemed necessary by the latest grading plan (GAC Engineering and Land Surveying, 5 sheets, 10-scale, latest revision dated 1-11-22). Comment No. 2: Please provide a statement addressing the potential impact of the proposed project on adjacent off-site properties from a geotechnical standpoint. Response to Comment No. 2: In GSI’s opinion, the proposed project will have no significant impact on adjacent off-site properties, provided the recommendations presented in the referenced report are incorporated into the design and construction of the proposed project. Comment No. 3: Please provide an updated “Test Pit Location Map” utilizing the most current version of the grading plan for the project as the base map and at a sufficiently large scale to clearly show (at a minimum): a) existing site topography, b) proposed structures and improvements, c) proposed finished grades, d) geologic units, e) limits of proposed remedial grading, and f) the limits of subsurface exploration. Response to Comment No. 3: The requested updated Test Pit Location Map is attached as Figure 1. Comment No. 4: Strength (direct shear) testing of the on-site soils is not provided in the reviewed report. Please provide the appropriate laboratory testing to substantiate the values for bearing capacity, passive pressure, coefficient of friction, and active pressure that are presented in the report. If presumptive values are being recommended by the consultant, please state the reference and use values consistent with the appropriate soil type in Tables 1806.2 and 1610.1 of the 2019 California Building Code. The reviewer notes that several of the geotechnical values presented for use in the report exceed soil Class 4 per Table 1806.2. If soil parameters other than soil class 5 in Table 1806.2 are provided, please justify the soil type by laboratory testing. Response to Comment No. 4: GSI performed a preliminary geotechnical investigation for the large residential tract just north of the subject site, including shear testing. The formational material is the same for both sites and, in our judgement, was reasonably applicable. However, we understand A.C. Mattos, Inc.W.O. 8320-A1-SC 2780 James Drive, Carlsbad January 23, 2023 File: e:\wp21\8300\8320a1.rtc Page 2 GeoSoils, Inc. only from the City (citing their guidelines) that shear test data from immediately adjacent sites may be applied. Our parameters were based on our experience and judgement. However, presumptive values have been applied to expedite report review. Accordingly, values from Table 1806.2 of the 2019 California Building Code are applied: an allowable bearing value of 2,000 psf (pounds per square foot), a friction value of 0.25 and a lateral resistance value of 150 pcf (pounds per square foot per foot) should be used for foundation design. Comment No. 5: Please clarify the recommendations for concrete design from a geotechnical standpoint, as it appears strength values of 2,500 psi (page 39) and 4,000 psi (page 36) are provided along with a w/c ratio of 0.50. Response to Comment No. 5: The strength value of 2,500 psi was provided for exterior concrete slab design. The 4,000 psi strength quoted is a typo, and GSI thanks the reviewer for pointing this out. The w/c ratio provided (page 25) is for reducing the potential for water vapor transmission through interior slabs. Comment No. 6: Please evaluate and discuss the potential for storm water infiltration at the subject site as part of the proposed development. Response to Comment No. 6: The site is classified by the USDA (United States Department of Agriculture website) Soil Conservation Service, as the Carlsbad Gravelly Loamy Sand. It is described as moderately well-drained, and classified as HSG “B,” (KSAT = 1.98 to 5.95 in/hi [high]). Although it appears the soil is potentially receptive to infiltration from storm water basins, there is a potential for seepage to perch on the denser formational or fill materials underlying the site and area, leading to mounding causing impaired performance of structural foundations and other hardscape features, both onsite and offsite. It is poor engineering judgement to recommend discharge of storm water adjacent to settlement-sensitive improvements, potentially causing distress, and a “no infiltration” category is recommended. Comment No. 7 Please add observation of temporary slopes to the list of geotechnical observations/testing services that should be provided during the construction of the proposed development. Response to Comment No. 7: This recommendation is already presented on Page 16 of the subject report. A.C. Mattos, Inc.W.O. 8320-A1-SC 2780 James Drive, Carlsbad January 23, 2023 File: e:\wp21\8300\8320a1.rtc Page 3 GeoSoils, Inc. The opportunity to be of service is sincerely appreciated. If you should have any questions, please do not hesitate to contact our office. Respectfully submitted, GeoSoils, Inc. Todd M. Page Stephen J. Coover Engineering Geologist, CEG 2083 Geotechnical Engineer, GE 2057 TMP/JPF/SJC/sh Attachment:Figure 1 - Test Pit Location Map Distribution:(1) Addressee (PDF via email) (1) Greg Caudill (PDF via email - gcaudill.gac@gmail.com) A.C. Mattos, Inc.W.O. 8320-A1-SC 2780 James Drive, Carlsbad January 23, 2023 File: e:\wp21\8300\8320a1.rtc Page 4 W.O.DATE:SCALE:8320-A1-SC 01/23 1" = 20' Figure 1 TEST PIT LOCATION MAP ALL LOCATIONS ARE APPROXIMATE This document or efile is not a part of the Construction Documents and should not be relied upon as being an accurate depiction of design. TP-4 TP-5 TP-3 TP-1 TP-2 N.A.P. N.A.P.N.A.P. N.A.P. Qop Afc Qop Afc Afc Qop TP-5 N.A.P. GSI LEGEND Afu Afc Qop Afu N