15 ATTACHMENT 9 - Laserfiche WebLink

Project No. 9929.G Geotechnical Investigation/Vineyard Avenue, Pleasanton 8 August 2003 57. Retaining walls or sound walls may either be founded on a spread footing or a pier foundation. A spread footing foundation may only be used where there is a minimum of 10 feet of cover between the slope surface and the front face of the footing at foundation level. Spread footings should have a minimum depth of 18 inches below the lowest adjacent pad grade (i.e. trenching depth). Design bearing pressures for footings should not exceed 2,200 p.s.f. due to dead plus sustained live loads and maybe increased by 113 due to all loads which include wind or seismic. To accommodate lateral building loads, the passive resistance of the foundation soil can be utilized. The passive soil pressures can be assumed to act against the front face of the footing below a depth of one foot below the ground surface or driveway subgrade. It is recommended that a passive pressure equivalent to that of a fluid weighing 275 p.c.f. be used. In addition, an allowable friction coefficient of 0.30 can be assumed at the base of the spread footings. 58. Piers should be designed on the basis of skin friction acting between the soil and that portion of the pier that extends below a depth of two feet below finished grade. For the soils at the site, an allowable skin friction value of 400 p.s.f. can be used for combined dead and live loads. This value can be increased by one-third for total loads which include wind or seismic forces. Spacing should be determined as required by the load distribution, but minimum spacing should not be less than 3 pier diameters, center to center. Maximum spacing and the minimum depth of piers is to be determined by the Structural Engineer. 59. To resist lateral loads, the passive resistance of the soil can be used. The soil passive pressures can be assumed to act against the lateral projected area of the pier described by the vertical dimension of twice the pier diameter. It is recommended that a passive pressure equivalent of that of a fluid weighing 275 p.c.f. be used below one foot. 60. It is important that care be exercised to ensure that any concrete spills during the concrete pour must be removed and no "mushrooming" effects are allowed to remain around the top of the pier. TERRASEARCH, inc. Page 27 of 53