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Home My WebLink AboutSL08639-12 San Luis Ranch SER Update LetterGEO...� Boa—u-rior�:� June 12, 2018 SL08639-12 Client: Al Entitlement IV, LLC C/o Coastal Community Builders Mr. Dave Daniels Post Office Box 13 Pismo Beach California 93449 Project name: Tract 3096 San Luis Ranch San Luis Obispo California 220 High Street San Luis Obispo CA 93401 805.543.8539 1021 Tama Lane, Suite 105 Santa Maria, CA 93455 805.614.6333 PO Box 30159 Santa Barbara, CA 93105 805.966.2200 SOILS ENGINEERING REPORT UPDATE LETTER- 2016 CBC Dear Mr. Daniels: This letter has been prepared as an update to the project Soils Engineering Report for the proposed San Luis Ranch Development located east of Madonna Road, west of the 101 freeway and south of Dalidio Drive in San Luis Obispo, California. It is our understanding that the referenced Soils Engineering Report originally prepared by GeoSolutions, Inc. (GeoSolutions, Inc., 2013) was submitted to the building department for permitting of this project. Based on changes to the California Building Code since preparation of the original report, revised seismic design information is presented below in accordance with the 2016 California Building Code. The recommendations for site preparation, grading, foundations and lateral earth pressures are still valid for the subject property, and should be utilized in design of the proposed development. The following information should be considered as an addendum to the referenced Soils Engineering Report (GeoSolutions, Inc., 2013). SEISMIC DESIGN CONSIDERATIONS Estimating the design ground motions at the Site depends on many factors including the distance from the Site to known active faults; the expected magnitude and rate of recurrence of seismic events produced on such faults; the source -to -site ground motion attenuation characteristics; and the Site soil profile characteristics. According to section 1613 of the 2016 CBC (CBSC, 2016), all structures and portions of structures should be designed to resist the effects of seismic loadings caused by earthquake ground motions in accordance with the ASCE 7 2010 Minimum Design Loads for Buildings and Other Structures, hereafter referred to as ASCE7-10 (ASCE, 2013). The Site soil profile classification (Site Class) can be determined by the average soil properties in the upper 100 feet of the Site profile and the criteria provided in Table 20.3-1 of ASCE7-10. Spectral response accelerations, peak ground accelerations, and site coefficients provided in this report were obtained using the computer -based U.S. Seismic Design Map tool available from the United States Geological Survey website (USGS, 2013). This program utilizes the methods developed in the 1997, 2000, 2003, 2008 and 2013 errata editions of the NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures in conjunction with user -inputted Site latitude and longitude coordinates to calculate seismic design parameters and response spectra (both for period and displacement) for soil profile Site Classes A through E. Site coordinates of 35.25612 degrees north latitude and-120.643573 degrees west longitude were used in the web -based probabilistic seismic hazard analysis (USGS, 2013). Based on the results from the in -situ tests performed during the field investigation, the Site was defined as Site Class E, "Soft Soil' profile per ASCE7-10, Chapter 20. Relevant seismic design parameters obtained from the program area summarized in Table 1: Seismic Design Parameters. info@geosolutions.net sbinfo@geosolutions.net San Luis Ranch June 12 2018 Project SL08639-12 Table 1: Seismic Design Parameters Site Class E "Soft Soil' Seismic Design Category D 1-Second Period Design Spectral Response Acceleration, SD1 0.711 g Short -Period Design Spectral Response Acceleration, SDs 0.698 g Site Specific MCE Peak Ground Acceleration, PGAm 0.425 g LIQUEFACTION HAZARD ASSESSMENT As reported previously in the referenced Soils Engineering Report (GeoSolutions, Inc, 2015) the potential for seismic liquefaction of Site soils is high. Liquefaction was determined to likely occur in the sandy soil layers located between the depths of 13 to 50 feet below ground surface and seismically induced settlements were estimated to be on the order of 1.0 to 3.5 inches. Based on the depth to the potentially liquefiable sand layers and the scope of the proposed development, we anticipate that seismically induced settlements would likely be associated with general subsidence of land mass, with seismically induced differential vertical displacements of less than 1 inch over a horizontal distance of 30 feet. Total seismically induced vertical settlements are anticipated to be a maximum of 3.5 inches. As the Site is generally flat, seismically induced lateral displacement is anticipated to be negligible. According to Section 8.0, Mitigation of Liquefaction Hazards of the DMG Special Publication 117 (SCEC, 1999) and the County of Los Angeles Department of Public Works Manual for Preparation of Geotechnical Reports (County of Los Angeles, 2013), structural mitigation, without the use of ground improvement, for liquefiable sites is acceptable provided the following criteria are satisfied: (1) Seismically induced differential vertical displacements are less than 1 inch over a horizontal distance of 30 feet; (2) Total seismically induced vertical settlements are less than 4 inches; and (3) Seismically induced lateral displacements are less than 12 inches. As the results of our liquefaction analysis are within the limits set forth by SCEC and the County of Los Angeles, no special ground improvement is required for development of this project and the effects of liquefaction induced settlements may be mitigated with structural design elements. CLOSURE This report is issued with the understanding that it is the responsibility of the owner or his/her representative to ensure that the information and recommendations contained herein are brought to the attention of the architect and engineer for the project, and incorporated into the project plans and specifications. The owner or his/her representative is responsible to ensure that the necessary steps are taken to see that the contractor and subcontractors carry out such recommendations in the field. As of the present date, the findings of this letter are valid for the property studied. With the passage of time, changes in the conditions of a property can occur whether they are due to natural processes or to the works of man on this or adjacent properties. Therefore, this letter should not be relied upon after a period of 3 years without our review nor should it be used or is it applicable for any properties other than those 2 162e135alutions, tNE. Geotechnical, Geologic & Environmental Services San Luis Ranch June 12 2018 Project SL08639-12 studied. However many events such as floods, earthquakes, grading of the adjacent properties and building and municipal code changes could render sections of this report invalid in less than 3 years. Thank you for the opportunity to have been of service in preparing this report. If you have any questions or require additional assistance, please feel free to contact the undersigned at (805) 543-8539. Sincerely, GeoSolution t LLJ ry 61361 a Kraig R. Cro i Principal, C61 (pp�CIV1� ;" 'J - 2285 San Luis Drive SER Update Letter.doc References: Soils Engineering Report, 2285 San Luis Drive, APN: 001-082-016, San Luis Obispo California, by GeoSolutions, Inc., Project SL08618-1 (Revision 1), dated December 19, 2013. 3 GeoSolutions, INN. Geotechnical, Geologic & Environmental Services