3A Public Hearing 2006 1204 - Laserfiche WebLink

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GEOTECNIA Project Number: 060805 2888 Darius Way, San Leandro October 27,2006 Page 7 Temporary Slopes, Shoring, and Underpinning Temporary cut slopes higher than 4 feet should be constructed in accordance with applicable codes and regulations. We recommend that the inclination of unsupported temporary cut slopes at the site be 1:1 in the bedrock and 1.5:1 in the clay soils, provided the work is done during the dry season, unless we change this recommendation during construction. If excavation occurs during the wet season, flatter temporary slopes or other measures may be required to support temporary slopes. The safe inclinations of unsupported cut slopes should be determined by a representative of our firm during construction. GEOTECNIA should continue to be retained to observe the earth materials exposed during excavation in order to observe the bedding planes, fracture and joint orientations, presence of clay lenses, and evaluate the stability of the exposed cut slopes. In bedrock areas where the orientation of the discontinuities is favorable relative to the orientation of the cut slope and the bedrock is not slickensided, a 1: 1 or even steeper slope may be used. In bedrock areas with weaker layers, excessive slickensides, adverse orientation of the discontinuities relative to the orientation of the cut slope, or where seepage is present, the slope may need to be laid back to flatter than 1: 1. If the height of the cut slope exceeds 10 feet vertically, an intermediate bench may be required or a debris fence may need to be installed along the base of the slope. In addition, all existing improvements at the site in the immediate vicinity of proposed excavations must be protected during construction. The proposed construction methods should provide for shoring and underpinning as required to protect the adjacent improvements. The stability of temporary slopes and the design of shoring or underpinning are the responsibility of the contractor. GEOTECNIA will continue to be available to assist the contractor or shoring designer as required. Foundations General The majority of the proposed structures at the site should be supported on drilled piers; however, the portions of the structures in level areas underlain by bedrock north of the access road may be supported on shallow spread and continuous footing foundations. Recommendations are presented below for both drilled piers and shallow footings. Drilled Piers Drilled piers should be used to support the majority ofthe proposed buildings and retaining walls at the site. The piers should be at least 18 inches in diameter and extend to a depth of at least 16 feet below the ground surface or below the bottom of the grade beam or penetrate at least 10 feet into the gabbro bedrock, whichever is deeocr. The actual depth should be determined in the field