Seismic Response Analyses for the Silicon Valley Rapid Transit Project

This study presents results from one-dimensional seismic ground response analyses, performed for the Silicon Valley Rapid Transit (SVRT) project. Due to the large amplitude of the design input motion, large levels of shear strain are calculated in the soil column that are highly sensitive to modeling details. Critical issues affecting the results include: (1) the use of an innovative stress-strain (backbone) curve that captures expected behavior at small strains from empirical modulus reduction models along with expected large strain behavior as represented by material-specific rate-adjusted shear strengths; (2) assessment of velocity variability and randomness from variable stratigraphy (conditional on depth and soil type) on the computed response; (3) comparison of results computed from equivalent-linear and nonlinear codes; and (4) use of empirical amplification factors to help identify potential limitations of the results obtained from ground response analysis. Consideration of these issues indicates that our results are generally reasonable to use as input to subsequent soil-structure interaction analyses.