Evaluation of p-y curves attendant to lateral resistance of micropiles in Franciscan Assemblage sandstone and shale; North Anchorage Housing, Golden Gate Bridge, California

摘要

Since construction of the Golden Gate Bridge in 1937, seismic codes have changed requiring seismic design and retrofit of the original foundation and structures. The seismic retrofit program for the bridge was divided into three phases. The North Anchorage Housing (Phase III) retrofit program is currently in progress.In 2005, to evaluate the lateral resistance, as p-y curves, of the micropile anchors in the Franciscan rock, we employed computer program LPile. Subsequent to our initial analysis of the p-y curves, new input parameters for rock have been developed for LPile. In 2010, we used the methodology described in p-y Criterion for Rock Mass to develop p-y curve data facilitated with p-y Rock, a special computer code employing generalized Hoek-Brown rock strength criterion. Required rock input includes: intact rock strength, unit weight, geologic strength index (GSI), deformation modulus and Poisson's ratio. The results demonstrate little difference between the original and new p-y curves for the weak poor rock. However, for stronger, better quality rock, the p-y curves diverge because the rock displays higher resistance to lateral pressure. The p-y curves are sensitive to the GSI and deformation modulus of the rock mass. The results demonstrate new LPile input parameters for rock sockets give the designer a more realistic estimate of lateral resistance in rock sockets.