Centrifuge Modeling Studies of Site Response in Soft Clay over Wide Strain Range

摘要

Centrifuge models of soft-clay deposits were shaken with suites of earthquake ground motions to study site response over a wide strain range. The models were constructed in an innovative hinged-plate container to effectively reproduce one-dimensional ground-response boundary conditions. Dense sensor arrays facilitate back-calculation of modulus-reduction and damping values that show modest misfits from empirical models. Low-amplitude base motions produced nearly elastic response in which ground motions were amplified through the soil column, and the fundamental site period was approximately 1.0 s. High-intensity base motions produced shear strains higher than 10％, mobilizing shear failure in clay at stresses larger than the undrained monotonic shear strength. The authors attribute these high mobilized stresses to rate effects, which should be considered in strength-parameter selection for nonlinear analysis. This nonlinear response deamplified short-period spectral accelerations and lengthened the site period to 3.0 s. The nonlinearity in spectral amplification is parameterized in a form used for site terms in ground-motion prediction equations to provide empirical constraint unavailable from ground-motion databases.