CONFIRMATION OF SUBSURFACE GEOLOGIC CONDITIONS OF THE UC BERKELEY STANLEY HALL REPLACEMENT PROJECT BY CONSTRUCTION FIELD OBSERVATIONS

A field geologic mapping program is being implemented to confirm the presence of heterogeneous and faulted bedrock materials beneath the Stanley Hall Replacement Project on the campus of the University of California Berkeley, in Berkeley, California, USA. As part of a comprehensive seismic upgrade of campus facilities, a seven story biosciences building is under construction on a site adjacent to the Louderback Shear Zone, an ancestral fault structure of the nearby active Hayward Fault Zone. Sheared shale, graywacke sandstone, metagraywacke and other rocks of the Jurassic-Cretaceous Franciscan Assemblage were observed during a detailed geotechnical and geologic investigation program. The program consisted of deep borings utilizing undisturbed and drive sampling and diamond coring to depths of 160 feet, geophysics including spectral analysis of surface waves (SASW) and seismic refraction, as well as laboratory testing for strength and index properties. Geotechnical design criteria for shoring systems including permanent soil-nail walls, possible underpinning of a nearby structure, micropile foundation elements to resist seismic forces, and dewatering were provided based on analysis of the investigation results. Field mapping of the 75-foot deep excavation is important for several reasons; 1) identification of zones of potentially unstable rock associated with faulting, adverse bedding and joint planes, seepage and pervasive shearing. that could impact the soil nail system; 2) confirmation of the presence of the Louderback Shear Zone and previously mapped paleochannels that will build on the current geologic understanding of the Berkeley Hills; and 3) integration of geologic observation and construction of deep excavations will provide valuable information for future projects of this magnitude and complexity.