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Home My WebLink AboutCT 2018-0004; THE SEAGLASS; GEOTECHNICAL MEMORANDUM; 2020-12-16Geotechnical 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 TECHNICAL M E M O R A N D U M DATE: December 16, 2020 W.O. 7544-C-SC TO: 2646 Sea Glass, LLC c/o Prophet Solutions 5845 Avenida Encinias, Suite 138 Carlsbad, California 92008 Attn: Mr. Rod Boone From: Robert G. Crisman, CEG 1934 David W. Skelly, RCE 47857 Subject: Review of Revised Plans, Including a New Retaining Wall Located Along the Southern Property Line at “The Sea Glass,” 2646 State Street, Carlsbad, California References: 1. “Structural Calculations Package, Retaining Wall Calculations, State Street Condominiums, 2646 State Street, Carlsbad, Ca. 92008, P.N. 17090087, dated October 6, 2020, by Patterson Engineering, Inc. 2. “Grading Plans for: The Sea Glass,” P.N. CT2018-0004, DWG 519-2, Latest Revision (retaining wall details) dated October 7, 2020, by Van Ryn Engineering 3. “Revised Report of Geotechnical Observation and Testing During Grading, “The Sea Glass,” 2646 State Street, Carlsbad, California,” W.O. 7544-B-SC, dated June 3, 2020, by GeoSoils, Inc. 4. “Geotechnical Update for “The Sea Glass,” 2646 State Street, Carlsbad, California 92008,” W.O. 7452-A-SC, Dated May 31, 2018, by GeoSoils, Inc. 5. “Geotechnical Evaluation, ‘The Wave,’ 2646 State Street, Carlsbad, San Diego County, California,” W.O. 6935-A-SC, dated November 3, 2015. In accordance with your authorization, GeoSoils, Inc. (GSI) has prepared this review regarding revisions to the site plans (see Reference No. 1) with respect to the addition of a new retaining wall along portions of the southern property line. The purpose of our review is to evaluate and comment on the planned design and construction of this wall for the intended use and for conformance with the intent of the referenced geotechnical reports. The scope of work included: a review of the revised plans prepared by Van Ryn Engineering, Inc. (Reference No. 1), a review of the wall calculations package, prepared by Patterson Engineering (Reference No. 2), a review of relevant geotechnical reports • GeoSoils, Inc.2646 Sea Glass, LLC W.O. 7544-C-SC 2646 State Street, Carlsbad December 16, 2020 File:e:\wp12\750\7544c.ror Page 2 prepared by this office, a review of unpublished comments from the City, engineering and geologic analysis, and preparation of this memorandum. Unless specifically superceded herein, the conclusions and recommendations presented in the referenced GSI documents remain valid and applicable. Based on our review, the following comments and additional recommendations are provided: Calculation Package (Reference No. 2) Review: 1. Based on the site soil conditions, soil design parameters applied in Reference No. 2 appear to be suitable for use in wall design/construction, from a geotechnical viewpoint. It should be noted that original retaining wall design and construction recommendations for this project are presented in Reference No. 5. As indicated previously, unless superceded herein, the recommendations presented in Reference No. 5 are considered valid and applicable. 2. City comments indicate that Reference No. 2 shall be “updated to latest 2019 CBC Code.” From a geotechnical viewpoint, any seismic design parameters necessary for the calculation package update may be derived from the following Table. Seismic Shaking Parameters Based on the site conditions, the following table summarizes the updated site-specific design criteria obtained from the 2019 edition of the California Building Code, Chapter 16 Structural Design, Section 1613, Earthquake Loads. The computer program “OSHPD Seismic design Maps,” provided by a joint effort between the Structural Engineers Association of California and the Office of Statewide Health Planning and Development ([OSHPD] SEAC/OSHPD, 2020) was utilized for design (http://seismicmaps.org). The short spectral response utilizes a period of 0.2 seconds. 2019 CBC SEISMIC DESIGN PARAMETERS PARAMETER VALUE 2019 CBC/ASCE REFERENCE Risk Category II Table 1604.5 Site Class (top 100 feet)C Section 1613.2.2/ Chap. 20 ASCE 7-16 (p. 203-204) sSpectral Response - (0.2 sec), S 1.081 g Section 1613.2.1 Figure 1613.2.1(1) 1Spectral Response - (1 sec), S 0.391 g Section 1613.2.1 Figure 1613.2.1(2) aSite Coefficient, F 1.2 Table 1613.2.3(1) vSite Coefficient, F 1.5 Table 1613.2.3(2) Maximum Considered Earthquake Spectral MSResponse Acceleration (0.2 sec), S 1.297 g Section 1613.2.3 (Eqn 16-36) I I I I GeoSoils, Inc. 2019 CBC SEISMIC DESIGN PARAMETERS PARAMETER VALUE 2019 CBC/ASCE REFERENCE 2646 Sea Glass, LLC W.O. 7544-C-SC 2646 State Street, Carlsbad December 16, 2020 File:e:\wp12\750\7544c.ror Page 3 Maximum Considered Earthquake Spectral M1Response Acceleration (1 sec), S 0.587 g Section 1613.2.3 (Eqn 16-37) 5% Damped Design Spectral Response DSAcceleration (0.2 sec), S 0.865 g Section 1613.2.4 (Eqn 16-38) 5% Damped Design Spectral Response D1Acceleration (1 sec), S 0.391 g Section 1613.2.4 (Eqn 16-39) MPGA - Probabilistic Vertical Ground Acceleration may be assumed as about 50% of these values. 0.573 g ASCE 7-16 (Eqn 11.8.1) Seismic Design Category D Section 1613.2.5/ASCE 7-16 (p. 85: Table 11.6-1 or 11.6-2) GENERAL SEISMIC DESIGN PARAMETERS PARAMETER VALUE Distance to Seismic Source (Newport-Inglewood fault) ±4.5 mi (7.3 km)(1) WUpper Bound Earthquake (Newport-Inglewood fault) M = 7.1(2) - From Blake (2000)(1) - Cao, et al. (2003)(2) Conformance to the criteria above for seismic design does not constitute any kind of guarantee or assurance that significant structural damage or ground failure will not occur in the event of a large earthquake. The primary goal of seismic design is to protect life, not to eliminate all damage, since such design may be economically prohibitive. Cumulative effects of seismic events are not addressed in the 2019 Edition of the CBC and regular wmaintenance and repair following locally significant seismic events (i.e., M 5.5) will likely be necessary, as is the case in all of southern California. Grading Plan (Reference No. 1) Review: Based on our review, the plans appear to be in conformance with the intent of the reference geotechnical reports and GSI recommendations, with the following comments. Details F, G, and H, shown on Sheet 4.1 of Reference No. 1 present the schematic relationships between the planned wall and the existing offsite structure. Detail H shows the planned wall in contact with the existing building wall, with the interface between the two structures filled with an “expansion joint filler,” while Details F and G show a gap between the two structures. I I I I I I I I GeoSoils, Inc.2646 Sea Glass, LLC W.O. 7544-C-SC 2646 State Street, Carlsbad December 16, 2020 File:e:\wp12\750\7544c.ror Page 4 Based on a review of Details F and G, it appears that a ½ inch pvc “weep hole” is added to allow water (storm water) collected within the gap shown on Details F and G to drain through the wall, and into the subject site. By convention, this is generally not allowed, as water would be draining into the retained area behind the wall. However, while not shown on the details, the retained material behind the wall in Details F and G is anticipated to consist of a free draining, open graded rock medium that is part of the planned pervious paver system (i.e. reservoir rock) within the projects driveway area. This paving system includes it own drainage system so that any water entering the site from the weep holes would be directed into the pervious pavement section and pavement drainage system. In order to ensure that this configuration functions adequately, it is recommended that any soil backfill behind the wall (if used) is placed no higher than the bottom of the weep holes, and that the soil subgrade surface along the base of the reservoir rock is sloped at least 1 percent down and away from the back of the wall. The need for water proofing of the exterior face of the existing offsite building should be evaluated by the project Architect. Weep hole spacing should be provided by the project Civil Engineer. The weep system will require periodic maintenance to keep from clogging and perform adequately. Closure The conclusions and recommendations presented herein 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. This report may be subject to review by the controlling authorities.