3.2 - Laserfiche WebLink

Home Browse Search

Suzanne Davisz July 8, 1998 Page 2 L3118 SITE CONDITIONS The lot has been previously graded and is characterized by cut and fill areas forming the building pad for the existing fire damaged residence, driveway, and swimming pool on the western half of the lot. A moderately steep (18 percent inclination), east-facing slope is present on the eastern half of the lot. Steep (47 percent inclination), cut and fill slopes are located in the vicinity of the existing residence. Site drainage is characterized by sheetflow to the east, with some runoff collected into a small swale along the southern property boundary. The existing flatwork (concrete driveway and walkways), retaining walls, and foundation of the existing residence do not show signs of significant distress. The Town Geologic Map indicates that the house site is underlain, at depth, by bedrock materials of the Santa Clara Formation (conglomerate, sandstone, siltstone, and claystone). The bedrock is in turn overlain by clayey sand to silty clay (potentially expansive soil,colluvium, alluvium, and artificial fill). No direct exposure of bedrock was observed on the subject property.The mapped traces of the potentially active Monta Vista fault and the active San Andreas fault are 2,000 feet northeast and 3.5 miles southwest, respectively,from the subject property. CONCLUSIONS AND RECOMMENDED ACTION The proposed development is constrained by potential soil creep, expansive soils, and the susceptibility of the site to strong seismic ground shaking. It appears that moderate grading operations will be performed to construct the new residence. We understand that site drainage design will be addressed to the satisfaction of the Town Engineer. The basic site development plan appears geotechnically feasible and we have no geotechnical objections to the proposed development plan. Prior to issuance of permits for construction,the Project Geotechnical Consultant should review all geotechnical aspects of building plans including specific evaluation of the design and placement of the proposed swimming pool, foundation, cut and fill, and drainage alterations. Consequently, we recommend geotechnical approval of permits for project construction with the following conditions: 1. Geotechnical Plan Review - The applicant's geotechnical consultant should characterize anticipated peak and repeatable seismic ground motion in percent gravity for consideration by the project structural engineer. The current standard-of-care design for foundation piers within the Town with similar soil conditions is a minimum 16-inch diameter pier reinforced with a minimum of four#5 vertical rebars. These standards should be considered by the consultant. The applicant's geotechnical consultant shall review and approve all geotechnical aspects of the development plans (i.e., site preparation and grading, site drainage improvements and design parameters for the foundation, retaining walls, and swimming pool) to ensure that their recommendations have been properly incorporated. COTTON, SHIRES & ASSOCIATES, INC.