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Home My WebLink About4.1 SupplementalCOTTON, SHIRES AND ASSOCIATES, INC. CONSULTING ENGINEERS AND GEOLOGISTS TO: Brian Froelich Associate Planner TOWN OF LOS ALTOS HILLS 26379 Fremont Road Los Altos Hills, California 94022 SUPPLEMENT AGENDA ITEM # 14A Distributed: 2-1 August 13, 2013 L5233 SUBJECT: Geotechnical Peer Review RE: ISCA Assets, LLC, Maior Additional and Remodel 251-13-SD-GD-ZP 27640 Sherlock Road At your request, we have completed a geotechnical peer review of the Site Development application for proposed site improvements using: • Geotechnical Investigation (report) prepared by Murray Engineers, Inc., dated June 12, 2013; • 'Architectural Plans _(18 sheets) prepared by Bekom Design, dated June 31, 2013; and- • Site Grading and Drainage Plans (7sheets, various scales) prepared by Lea & Braze Engineering, dated June 19, 2013. In addition, we completed a recent site reconnaissance and reviewed pertinent technical documents from our office files (L1019). DISCUSSION The applicant proposes to remodel and construct additions to the existing residence at the subject property including a second story element. The Project Geotechnical Consultant has recommended that portions of the existing residence that are supported by spread footings be upgraded with a drilled pier foundation. Impacted portions of the existing residence may need to be temporarily moved or rebuilt to allow replacement of supporting foundations. We understand that proposed improvements also include a replacement septic leachfield system, a swimming pool, and expansion of the existing driveway. The plans also call for a drainage retention system and drainage dissipater.. Provided estimates of project earthwork quantities includes 150 cubic yards of cut and 40 cubic yards of fill placement. Northern California Office 330 Village Lane Los Gatos, CA 95030-7218 (408) 354-5542 • Fax (408) 354-1852 Central California Office 6417 Dogtown Road San Andreas, CA 95249-9610 (209) 736-4252 • Fax (209) 736-1212 www rnftnn chiroc �nm Southern California Office 550 St. Charles Drive, Suite 108 Thousand Oaks, CA 91360-3995 (805) 497-7999 • Fax (805)497-7933 Brian Froelich Page 2 SITE CONDITIONS August 13, 2013 L5233 The existing house site is located along the relatively narrow crest of a ridge flanked by steep slopes. The southwestern portion of the residence extends over steep slopes, and we understand that this portion of the residence is supported on a pier foundation. The house site is underlain by relatively shallow greenstone bedrock of the Franciscan Complex. Flanking slopes to the west are mantled by sliver artificial fills and shallow colluvial soils that are potentially expansive. The mapped potentially active Berrocal Fault is located approximately 1,600 feet north of the subject property. CONCLUSIONS AND RECOMMENDED ACTION Proposed site construction is constrained by potentially expansive surficial soils, relatively minor existing artificial fill materials, and very strong seismic ground shaking. The Project Geotechnical Consultant has completed a site investigation and recommended geotechnical design criteria that are in general conformance with prevailing standards of geotechnical practice. Due to the steep flanking slopes, it is important that the Project Geotechnical Consultant carefully evaluate geotechnical design aspects of drainage retention and dissipater structures. We recommend that the following conditions be attached to geotechnical approval of the site development permit: 1. Geotechnical Plan Review - The applicant's geotechnical consultant should review and approve all geotechnical aspects of the project building and grading plans (i.e., site preparation and grading, site drainage improvements and design parameters for foundations, retaining walls and driveway) to ensure that their recommendations have been properly incorporated. The consultant should evaluate proposed placement and geotechnical design aspects of the drainage retention and dissipater structures. We suggest that multiple drainage dissipaters be considered at this site in strategic locations. The results of the plan review should be summarized by the geotechnical consultant in a letter and submitted to the Town Engineer for review along with other documents for building permit plan -check. 2. Geotechnical Construction Inspections - The geotechnical consultant should inspect, test (as needed), and approve all geotechnical aspects of the project construction. The inspections should include, but not necessarily be limited to: site preparation and grading, site surface and subsurface drainage improvements, and excavations for foundations and retaining walls prior to the placement of steel and concrete. The consultant should complete COTTON. SHTRES AND ASSOCTATES. INI Brian Froelich August 13, 2013 Page 3 L5233 an inspection of final site drainage improvements for conformance with geotechnical recommendations. The results of these inspections and the as -built conditions of the project should be described by the geotechnical consultant in a letter and submitted to the Town Engineer for review prior to final (as -built) project approval. LIMITATIONS This geotechnical peer review has been performed to provide technical advice to assist the Town with its discretionary permit decisions. Our services have been limited to-revie- of 4he ocLm_ *t ;previousl z i€lentified;- and a vt% review of...the.property.. Our opinions and conclusions are made in accordance with generally accepted principles and practices of the geotechnical profession. This warranty is in lieu of all other warranties, either expressed or implied. TS:DTS:kd Respectfully submitted, COTTON, SHIRES AND ASSOCIATES, INC. TOWN GEOTECHNICAL CONSULTANT Ted Sayre Principal Engineering Geologist CEG 1795 '19.I I I -� David T. Schrier Principal Geotechnical Engineer GE 2,334 COTTON- SUMPS ANn AS.SCK'IATRS. INE