Earthquake-induced nonlinear ground deformation analyses.
详细信息
文摘
The work in this dissertation investigates practical nonlinear computer analysis methods to evaluate earthquake induced permanent ground deformations, caused by soft soil behavior or liquefaction in cohesionless soil layers. Two existing computer programs (DESRA and TENSI) for dynamic site response analysis were modified and further developed. The new program DESRA-MUSC is applicable to a level ground site, while the program new TENSI-MUSC can be applied to a site with irregular surface and subsurface geometry, and/or with both horizontal and vertical input motions. Both programs were developed to allow response to be evaluated in total or effective stress modes. A loosely coupled pore pressure generation model enabled the evaluation of liquefaction potential of cohesionless soil layers and its consequences. Soil nonlinear behavior is simulated by a multiple-yielding-surface constitutive model and implemented by an explicit finite difference method. Transmitting base boundary conditions allow earthquake input motion be to applied at an appropriate firm soil interface at depth. A total Lagrangian algorithm was incorporated in the program TENSI-MUSC to model large deformations induced by strong earthquake shaking or liquefaction.;Several case studies are used to illustrate applications of the programs. These studies include both one-dimensional and two-dimensional examples. One-dimensional examples include comparisons between DESRA-MUSC and more conventional 'equivalent linear' SHAKE analyses. These analyses clearly indicated that SHAKE analyses should not be used for soft soil sites under strong earthquake shaking.;Two-dimensional examples include an idealized bridge embankment constructed on a liquefiable foundation soil, an idealized basin configuration, a complex bridge site and a typical hillside fill. Examples illustrate the influence of irregular subsurface soil stratigraphy, thickness of liquefiable layers, as well as initial static stress state on both ground response and permanent ground deformations. Liquefaction induced ground deformations are compared to the results from conventional Newmark deformation analysis. Differential ground motions across the sites and the resulting differential ground deformations are investigated for two-dimensional irregular soil configurations, and clearly show the importance of two-dimensional response in generating spatial incoherence of ground motion. Comparisons of one-dimensional and two-dimensional results suggest that two-dimensional models may be necessary for irregular soil geometry at important bridge sites.