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HomeMy WebLinkAboutCDP 2020-0027; MATTHEW RESIDENCE; RESPONSE TO THIRD-PARTY GEOTECHNICAL REVIEW FOR PROPOSED TWO-STORY, SINGLE FAMILY RESIDENCE, 5511 LOS ROBLES DRIVE, CARLSBAD, CA 92008; 2021-07-27EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. 10925 HARTLEY ROAD, SUITE "I" SANTEE, CALIFORNIA 92071 TEL. 619-258-7901 Arvin & Sepideh Matthew 215 Montclair Drive Danville, California 94526 July 27, 2021 Project No. 20-l 126G3 Subject: Response to Third-Party Geotechnical Review for Proposed Two-Story, Single-Family Residence 5511 Los Robles Drive Carlsbad, CA 92008 References: 1. Third Party Geotechnical Review (First), 5511 Los Robles Drive, Carlsbad, California, PD 2020-0027, by Hetherington Engineering Inc, dated May 25, 2021 . 2. "Geotechnical Investigation for Proposed Two-Story, Single-Family Residence, 5511 Los Robles Drive, Carlsbad, California 92008", Project No. 20-1126G3, Prepared by East County Soil Consultation and Engineering, Inc., Dated February 10, 2020. Dear Mr. & Mrs. Matthew: In accordance with your request, we have prepared this letter in response to the subject third- party geotechnical review by Hetherington Engineering, Inc. Comment No. 1 We have reviewed the grading plan prepared by John P. Strohminger and the foundation plans for the proposed two-story single-family residence and associated improvements at the subject site. The grading and foundation plans were found to be in accordance with the recommendations presented in the referenced geotechnical report (Reference No. 2). Comment No. 2 Please see attached figures showing an updated geotechnical map/plot plan (Figure 2) and geologic cross sections (Figure 3). Comment No. 3 Based on a review of our geotechnical report (Reference No. 2), site grading will consist of the removal and recompaction of the upper 2 feet of existing topsoil and terrace deposits for support Response to Third-Party Geotechnical Review for Proposed Two-Story, Single- Family Residence 5511 Los Robles Drive Carlsbad, California 92008 Page 2 July 27, 2021 Project No. 20-1126G3 of the proposed residence. The proposed two-story, single-family residence will be founded in properly compacted fill or medium dense terrace deposits. The foundations will consist of continuous footings, 18 inches deep and 15 inches wide and reinforced with four #4 bars, two near the top and two near the bottom. Floor slabs will be 5 inches thick and reinforced with #4 bars at 18 inches on centers in both directions. Floor slabs will be underlain by 2 inches of clean sand over a 10-mil visqueen moisture barrier over 2 inches of clean sand. Comment No. 4 From published geologic maps, the site is underlain at depth by sedimentary terrace deposits. There are no known geologic hazards such as landslides, liquefaction-prone areas, or earthquake faults at the site. However, the proposed building is subject to ground shaking and possible damage from earthquakes on nearby, or more distant, active faults. There are no mapped earthquake faults at the site. The closest major active fault is the offshore Newport-Inglewood Fault Zone located about 2 miles to the southwest. Comment No. 5 Please find the attached Figure 3 for current seismic design criteria based on ASCE 7-16 and the 2019 California Building Code. Comment No. 6 Based on the relatively high elevation of the property (El. 60), it is our opinion that the potential for tsunami damage is low. In addition, due the medium dense to dense consistency of the underlying terrace deposits, it our opinion that the potential for liquefaction is very low. Comment No. 7 Based on the dense consistency of the terrace deposits underlying the site at shallow depths and the minor depth of surface soil removal, it is our opinion that the proposed site grading and construction will not impact adjacent properties and existing improvements. Comment No. 8 Driveway and other exterior slabs may be supported on the extstmg soils provided they are scarified to a depth of 6 to 8 inches, moisture conditioned to near optimum moisture content and compacted to at least 90 percent relative compaction. Driveway and other exterior concrete slabs should be at least 5 inches thick and reinforced with No. 4 rebars spaced at 18 inches on centers in two directions and placed at mid-height in the slab. Driveway and other exterior slabs should be provided with construction joints spaced no more than 10 feet apart to minimize shrinkage cracking. Slab concrete should have a minimum compressive strength of 3,000 psi and maximum EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Response to Third-Party Geotechnical Review for Proposed Two-Story, Single- Family Residence 5511 Los Robles Drive Carlsbad, California 92008 PageJ July 27, 2021 Project No. 20-1126G3 water-cement ratio of 0.5 to minimize shrinkage cracking. No special testing of concrete is necessary. Some shrinkage cracking is still possible. Comment No. 9 Base on a review of the grading plans, low retaining walls will be constructed as part of site improvements. The retaining wall footings should be founded in either properly compacted fill or the medium dense to dense terrace deposits. Comment No. 10 Iotal and differential settlements of½ inch may be assumed for the proposed residence. Comment No. 11 Corrosivity tests were performed on a representative sample of the onsite soils. The attached test results (Figure 4) indicate a low degree of corrosivity. Accordingly, we recommend Type I/II Portland Cement for foundation construction. Comment No. 12 This comment has been addressed in our response in Comment No. 8. Comment No. 13 During site grading and construction, geotechnical observations and testing should consist of verification of the bottom of surface soil removals down to medium dense to dense terrace deposits, compaction testing verifying at least 90 percent relative compaction has been achieved, and observation of foundation excavations prior to the placement of reinforcing steel. These observations should be performed on an as needed basis. Comment No. 14 Please find attached Figure No. 5, listing codes, published maps and reports used m the preparation of the referenced geotechnical report (Reference No. 2). EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Response to Third-Party Geotechnical Review for Proposed Two-Story, Single- Family Residence 5511 Los Robles Drive Carlsbad, California 92008 Page 4 July 27, 2021 Project No. 20-1126G3 This opportunity to be of service is appreciated. If you have any questions, or we can be of further service, please do not hesitate to call or contact us. Respectfully Submitted, Martin R. Owen, PE, GE Geotechnical Engineer Attachments: Figures 1 through 5 EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Response to Third-Party Geotechnical Review for Proposed Two-Story, Single- Family Residence Pages July 23, 2021 Project No. 20-l 126G3 5511 Los Robles Drive Carlsbad, California 92008 58 FIGURE 1 GEOTECHNICAL MAP/PLOT PLAN 62 \ \ \ \ ' ~~ \ '~ ~V'~ APN 210-1!4-I! '~. ' \ \ ' \ \ // ' \ / A/ 62 / ' / /'/ /' g~ ~,(/M,4/c LL;c-4TJCW CF 7c:.7T ~wt:, 4)t, ~CG .b5!DS/TS ----LIA?/T.s OF G~//V~ EAST COUNTY SOIL CONSU LTATION AND ENGINEERING, INC. Response to Third-Party Geotechnical Review for Proposed Two-Story, Single- Family Residence 5511 Los Robles Drive Carlsbad, California 92008 FIGURE2 GEOLOGIC CROSS-SECTIONS Page 6 July 23, 2021 Project No. 20-1126G3 I I I • \(/}\III li,<i I / I ~ I ~\~ ~' !_ J -~--,g!ZF-! i H c> ~~i;;.!4~ (rt Ir -I ~!= ~ ~ C/VS.S-5i::C770N .;f--A ' ~ /~3:l?/ f '~t-/{j2:_~ --- 1E14=2 qt '~r~qt ~" ?,eo..55-~C/7t7AI 8-B / ~//b30/ EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Response to Third-Party Geotechnical Review for Proposed Two-Story, Single- Family Residence Page 7 July 27, 2021 Project No. 20-1126G3 5511 Los Robles Drive Carlsbad, California 92008 FIGUREJ SEISMIC DESIGN VALUES 5511 Los Robles Dr, Carlsbad, CA 92008, USA lo,l Date Design Code Reference Document Risk Category Site Class Type Value Ss 1.124 s, 0.404 s ,! 1.181 s...,, null • See Section 11.4.8 S:is 0.787 S:n null -See Section 114.8 Type Value soc null -See Section 1L4.8 F. 1.05 F. null -See Section 11.4.8 Description Description 7/19/2021. 1:54:10 PM ASCE7-16 II D · Stiff Soil MCE, ground motion. (for 0.2 second period) MCEq_ ground motion. (for 1.0s period) Site-modified spectral acceleration value Site-modified spectral acceleration value Numeric seismic design value at 0.2 second SA Numeric seismic design value at 1.0 second SA Seismic design category Site amplification factor at 0.2 second Site amplification factor at 1.0 second EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Response to Third-Party Geotechnical Review for Proposed Two-Story, Single- Family Residence 5511 Los Robles Drive Carlsbad, California 92008 FIGURE 4 CORROSIVITY TEST RES UL TS L A B O R A T O R Y R E P O R T Page 8 July 23, 2021 Project No. 20-1126G3 Telephone (619) 425-1993 Fax 425-7917 Established 1928 CLARKSON LABORATORY AND SUPPLY INC. 350 Trousdale Dr. Chula Vista, Ca. 91910 www .clarksonlab.com A N A L Y T I C A L A N D C O N S U L T I N G C H E M I S T S Date: July 12, 2021 Purchase Order Number: MATTHEW#l Sales Order Number: 52351 Account Number : EASCS To: *-------------------------------------------------* East County Soil Consultation and Engineering Inc . 10925 Hartley Road Suite I Santee, Ca 92071 Attention : Michael Duncan Laboratory Number : SO8301 Customers Phone: 258-7901 Fax: 258-7902 Sample Designation: *-------------------------------------------------* One soil sample received on 07/07/21 at 8:20am, taken from Matthew Los Robles Carlsbad. Analysis By California Test 643, 1999, Department of Transportation Division of Construction, Method for Estimating the Service Life of Steel Culverts. pH 8.2 Water Added (ml) 66 86 119 152 186 10 5 5 5 5 5 5 years years years years years to to to to to Water Soluble Water Sol.ubl.e RMB/arr perforation for a perforation for a perforation for a perforation for a perforation for a Sulfate Calif. Chl.oride Cal.if. 16 gauge 14 gauge 12 gauge 10 gauge 8 gauge Test 417 Test 422 metal metal metal metal metal Resistivity (ohm-cm) 9800 9400 7500 6700 6600 6900 7200 culvert. culvert. culvert. culvert. culvert. <0.003% 0.006% EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC. Response to Third-Party Geotecbnical Review for Proposed Two-Story, Single- Family Residence 5511 Los Robles Drive Carlsbad, California 92008 FIGURE 5 REFERENCES Page9 July 27, 2021 Project No. 20-1126G3 1. "2019 California Building Code, California Code of Regulations, Title 24, Part 2, Volume 2 of 2", Published by International Code Council. 2. "Geologic Map of the San Diego 30' x 60' Quadrangle, California", by Michael P. Kennedy and Siang S. Tan, 2008. 3. "Geotechnical and Foundation Engineering: Design and Construction", by Robert W. Day, 1999. 4. "Maps of Known Active Fault Near-Source Zones in California and Adjacent Portions of Nevada to be used with 1997 Uniform Building Code", Published by International Conference of Building Officials. 5. "Geologic Maps of the Northwestern Part of San Diego County, California", Department of Conservation, Division of Mines and Geology, by Siang S. Tan and Michael P. Kennedy, 1996. 6. "Bearing Capacity of Soils, Technical Engineering and Design Guides as Adapted from the US Army Corps of Engineers, No. 7", Published by ASCE Press, 1994. 7. "Foundations and Earth Structures, Design Manual 7.2", by Department of Navy Naval Facilities Engineering Command, May 1982, Revalidated by Change 1 September 1986. 8. "Ground Motions and Soil Liquefaction during Earthquakes", by H.B. Seed and I.M. Idriss, 1982. EAST COUNTY SOIL CONSULTATION AND ENGINEERING, INC.