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Home My WebLink AboutPD 2020-0007; FUKUDA ADDITION; GEOTECHNICAL UPDATE REPORT AND GRADING PLAN REVIEW; 2020-08-03iecordCj 10116126)0 COAST GEOTECHNICAL CONSULTING ENGINEERING GEOLOGISTS August 3, 2020 Lane Fukuda 2726 Morning Glory Lane Carlsbad, California 92008 W.O. 707419 fukt4L)1q 4oDtri0J S'D200 -000 1 e; S2- 2A C2o2O -x'' Subject: GEOTECHNICAL UPDATE REPORT AND GRADING PLAN REVIEW Proposed Second Story Addition and Basement 2726 Morning Glory Lane Carlsbad, California References: THIRD PARTY GEOTECHNICAL REVIEW (FIRST) Proposed Second Story Addition and Basement 2726 Morning Glory Lane Carlsbad, California Project ID: PD2020-0007 Prepared by Hetherington Engineering, Inc. Dated June 19, 2020 GRADING PLAN Fukuda Addition 2726 Morning Glory Lane Prepared by Rancho Coastal Engineering & Surveying, Inc. Dated May 20, 2020 and July 17, 2020 Scale: 1=5', Sheets 1, 3 and 4 PRELIMINARY GEOTECHNICAL INVESTIGATION Proposed Second Story Addition and Basement 2726 Morning Glory Lane Carlsbad, California Prepared by Coast Geotechnical Dated June 18, 2019 Dear Mr. Fukuda: At the time of our Preliminary Geotechnical Investigation Report, site plans, topographic surveys and grading plans were unavailable for review. This report presents an Update to our Preliminary Geotechnical Investigation Report, a Grading Plan Review and our response to the referenced third party review comments. P.O. BOX 230163 • ENCINITAS, CALIFORNIA 92023 (858) 755-8622 Coast Geotechnical August 3, 2020 W.O. P-707419 Page 2 of 8 GEOTECHNICAL UPDATE A review of the current grading plans prepared by Rancho Coastal Engineering and Surveying suggests that the development of the site is in substantial conformance with the design concepts anticipated in the Preliminary Geotechnical Investigation Report. Proposed Grading The grading recommendations including temporary slopes and alternate slot cuts remain applicable and should be implemented during the grading and construction phases. Temporary slopes and slot cuts should be observed by an Engineering Geologist. Additional recommendations may be necessary based on actual conditions revealed during grading. Foundations The foundation recommendations presented in the Preliminary Geotechnical Investigation Report remain applicable and should be implemented during the design and construction phases. Retaining Walls Retaining wall design parameters remain applicable and should be implemented in the design phase. Special consideration should be given to waterproofing, as indicated in the Preliminary Geotechnical Investigation Report. Dynamic (Seismic) Lateral Earth Pressures Potential seismic loading has been revised based on California Building Code (2019) and ASCE 7-16. For proposed restrained walls (non-yielding), potential seismic loading should be considered. For smooth rigid walls, Wood (1973) expressed the dynamic thrust in the following form: APe = khYH2 (nonyielding) P.O. BOX 230163 • ENCINITAS, CALIFORNIA 92023 (858) 755-8622 Coast Geotechnical August 3, 2020 W.O. P-707419 Page 3 of 8 where kb is /2 peak ground acceleration equal to 50 percent of the design spectral response acceleration coefficient (Sds) divided by 2.5 per C.B.C. (2007), Y is equal to the unit weight of backfill, and H is equal to the height of the wail. The pressure diagram for this dynamic component can be approximated as an inverted trapezoid with stress decreasing with depth. The point of application of the dynamic thrust is at a height of 0.6 above the base of the wall. The magnitude of the resultant is: .Pe = 18.8 H2 (nonyielding) This dynamic component should be added to the at-rest static pressure for seismic loading conditions. For cantilever walls (yielding), Seed and Whitman (1970) developed the dynamic thrust as: iPe = 3/8 kYH2 (yielding) - The pressure diagram for this dynamic component can be approximated as an inverted trapezoid with stress decreasing with depth and the resultant at a height of 0.6 above the base of the wall. The magnitude of the resultant is: APe = 7.1 H2 (yielding) This dynamic component should be added to the static pressure for seismic loading conditions. P.O. BOX 230163 • ENCINITAS, CALIFORNIA 92023 (858) 755-8622 Coast Geotechnical August 3, 2020 W.O. P-707419 Page 4 of 8 Seismic Considerations Although the likelihood of ground rupture on the site is remote, the property will be exposed to moderate to high levels of ground motion resulting from the release of energy should an earthquake occur along the numerous known and unknown faults in the region. The Newport/Inglewood Fault Zone located approximately 5.2 miles west of the property is the nearest known active fault, and is considered the design fault for the site. In addition to the Newport-Inglewood Fault, several other active faults may affect the subject site. Seismic design parameters were evaluated as part of this investigation in accordance with the 2019 California Building Code (CBC) and ASCE 7-16 Standard using the web-based United States Geological Survey (USGS) Seismic Design Tool. The generated results for the parameters are presented on Table 2. Table 2: Seismic Design Parameters Factors Values Site Class D Seismic Design Category 1/Il/ifi Site Coefficient, Fa 1.084 Site Coefficient, F N/A Mapped Short Period Spectral Acceleration, Ss 1.041 Mapped One-Period Spectral Acceleration, S1 0.378 Short Period Spectral Acceleration Adjusted for Site Class, SMS 1.128 One-Second Period Spectral Acceleration Adjusted for Site, SMI N/A Design Short Period Spectral Acceleration, SDS 0.752 Design One-Second Period Spectral Acceleration, SDI N/A P.O. BOX 230163' ENCINITAS, CALIFORNIA 92023 (858) 755-8622 Coast Geotechnical August 3, 2020 W.O. P-707419 Page 5 of 8 Site Classification For Seismic Design Site soils are classified based on the upper 100 feet maximum of site subsoil profile. In the absence of sufficient or specific site data, appropriate soil properties are permitted to be estimated by the project geotechnical consultant based on known geotechnical conditions, and Site Class D is typically used as a "default", unless otherwise noted. Site Classes A and B shall not be assigned to a site, if there is more than 10 feet of soil (or fill) between the top of the underlying rock surface and bottom of the foundation. Site Classes A and B are most commonly supported by shear wave velocity determination (Us, ft/s). Site Class F, which may require a site response analysis, consists of liquefiable or collapsible soils and highly sensitive clayey soil profile. Site Classes C, D, and E soils may be classified using an average field Standard Penetration Resistance (f) method for soil layers based on Section 20.4.2 of ASCE 7-16. Where refusal is met for a rock layer (blow counts of 50 or greater for 6 inches or less penetration), Ni is taken as 100 blows per foot. Site Classification is then established based on Table 20.3-1 of ASCE 7-16. Requirements provided below are also applicable and should be incorporated in the project designs where appropriate: I. Site specific hazard analysis is required (see Section 11.4.8) in accordance with Chapter 21.2 of ASCE 7-16 for structures on Site Class E sites with values of Ss greater than or equal to 1.0g, and structures on Site Class D and E sites with values of Si greater than or equal to 0.2g. However, the following 3 exceptions are permitted for Equivalent Lateral Force design (ELF) using conservative values of seismic design parameters in lieu of performing a site specific ground motion analysis: P.O. BOX 230163 • ENCINITAS, CALIFORNIA 92023 (858) 755-8622 Coast Geotechnical August 3, 2020 W.O. P-707419 Page 6 of 8 * Structures on Site Class E sites with Ss greater than or equal to 1.0, provided the site coefficient Fa is taken as equal to that of Site Class C. * For structures on Site Class D sites with Si greater than or equal to 0.2, a long period coefficient (Fv) of 1.7 may be utilized for calculation of Ts, provided that the value of Seismic Response Coefficient (Cs) is determined by Equation (12.8-2) for values of the fundamental period of the building (1) less than or equal to 1.5Ts, and taken as 1.5 times the value computed in accordance with either Equation 12.8-3 for T greater than 1.5 Is and less than or equal to TL or Equation 12.8-4 for T greater than U. * Structures on Site Class E sites with Si greater than or equal to 0.2, provided that T is less than or equal to Ts and the equivalent static force procedure is used for the design. Where Site Class B is recommended, and a site specific measurement is not provided, the site coefficients Fa, Fv, and FPGA shall be taken as unity (1.0) in accordance to Section 11.4.3 of ASCE 7-16. Where Site Class D is selected as the "default" site class per Section 11.4.3 of ASCE 7-16, the value of Fa shall not be less than 1.2. Where the simplified procedure of Section 12.4 is used, the value of Fa shall be determined in accordance with Section 12.14.8.1, and the values of Fv, SMS and SMI need not to be determined. At the project property massive dense and competent Pleistocene Very Old Paralic Deposits occur at very shallow depths on the order of 1.0 foot maximum below the existing ground surface (BGS), and based on our past experience with similar deposits, Site Class D (Stiff Soil), can be conservatively considered for the project site subsoil profile, unless otherwise noted. P.O. BOX 230163 • ENCINITAS, CALIFORNIA 92023 (858) 755-8622 Coast Geotechnical August 3, 2020 W.O. P-707419 Page 7 of 8 RESPONSE TO THIRD PARTY REVIEW Plans, grading, foundations and other pertinent data are addressed in this Updated Geotechnical Report and are consistent with the 2019 C.B.C. The current grading plans have been reviewed and are in general conformance with the recommendations of the Preliminary Geotechnical Investigation Report and this Updated Geotechnical Report. Geotechnical conditions, boring/test pit locations and other pertinent data are plotted on the enclosed Geotechnical Map which is based on the current grading plan. Revised Cross Sections A-A' and B-B', based on the current grading plan, depicting general subsurface conditions and slot cuts are included in this report. Our previous ABC Slot Cuts Excavation Detail, Figure 7, remains applicable and is included in this report. Seismic design parameters and seismic loading for retaining walls have been updated, based on ASCE 7-16. The following list of geotecimical observations/testing is recommended during the grading and construction phases. Observation of temporary cut slopes and slot cuts Observation of basement excavation Observation of wall backdrainage Density testing and observation during placement of wall baekfill Laboratory testing for Maximum Dry Density and Optimum Moisture Content for each soil type used as fill Observation of footing excavations prior to placement of steel Utility trench observation and testing P.O. BOX 230163 • ENCINITAS, CALIFORNIA 92023 (858) 755-8622 Coast Geotechnical August 3, 2020 W.O. P-707419 Page 8 of 8 6) The site location map is included on Page 6 of the Preliminary Geotechnical Investigation Report and is designated as Figure 1. LIMITATIONS All of the recommendations in the Preliminary Geotechnical Investigation Report which are not superceded by this report remain applicable and should be implemented during the design and construction phases. If you have any questions, please do not hesitate to contact us at (858) 755-8622. This opportunity to be of service is appreciated. Respectfully submitted, COAST GEOTECHNICAL 4u;oc Mau Kevin McFarland Project Geologist 9WA&~ Mark Burwell, C.E.G. Engineering Geologist FIGURES M"Lj-0,61 Vithayk Singhanet, P.E. Geotechnical Engineer f. ;Nov sc~l Figure 2: Geotechnical Map Figure 3: Geological Cross Section A-A' Figure 4: Geological Cross Section B-B' Figure 7: ABC Slot Cuts Excavation Detail P.O. BOX 230163 • ENCINITAS, CALIFORNIA 92023 (858) 755-8622 FIGURES I I Proposed Addition I • Existing Residence .1 Existing Grade O Test Pit Location Approximated D Boring Location Approximated L ' Qs Fill /Topsoil Very Old Paralic Deposits A' CROSS - SECTION A-A' 2726 MORNING GLORY LANE, CARLSBAD, CA I I --d SCALE: 1,1= 10' 0' 10' 20' A 170 - 165 - 160 - 155 - 150 - 145 - 140 135 130 - - I Existing GarageGarage Proposed Addition Existing 2.5 Existing Driveway Retaining Wall Ne T TP 2 \O Proposed af I Qs (Fill / Topsoil) - S, SIP Basement Cuts Qvop (Very Old Paralic Deposits) B-i T.D.13ft COAST GEOTECHNICAL 5931 Sea Lion Place, Suite 109 Project Number: 707419 Carlsbad. CA 92010 Figure Number: 3 Existing Covered Patio Existing Lawn af/ Qs (Fill 7.-Topsoil). . . . •: : • QvopVery 014 Paa1icDeposits) • •.•. • -. .: •.•.• :.•• . T.D.13ft 165 160 155 150 145 140 135 PL 2.5' Wall I Proposed Addition JI Proposed 5' Slot . Basement Cuts }I°t' CROSS -SECTION B-B' 2726 MORNING GLORY LANE, CARLSBAD, CA SCALE: 1"=lo' 1 1 I 0' 10' 20' Legend II Proposed Addition I Existing Residence .1 Existing Grade • Test Pit Location Approximated D Boring Location Approximated af I Qs J Fill /Topsoil I Very Old Paralic Deposits ®COAST GEOTECHNICAL 5931 Sea Lion Place. Suite 109 Project Number: 707419 Carlsbad, CA 92010 Figure Number: 4 PLAN VIEW Existing Covered Patio '1 Column Pad I N CROSS SECTION Existing Covered Patio Existing Column Pad \Temporary 1:1 Slope \ Slot Ct B\ I:1 NO SCALE Excavate Slot Cuts A and C, 5 feet wide not to exceed 6 feet. Construct wall in Slot Cuts A and C prior to Excavating Slot Cut B. ABC SLOT CUTS EXCAVATION DETAIL . COAST GEOTECHNICAL S931 Sea Lion Place. Suite log Carlsbad, CA92010 Project Number: 707419 Figure Number. 7