LASS-III, Computer Program for Seismic Response and Liquefaction of Layered Ground Under Multi-Directional Shaking

摘要

A new method of analysis is described for evaluation of seismic response and liquefaction of horizontally layered ground subjected to three components of earthquake base acceleration. Heretofore, only one component--the horizontal one with highest peak accleration--was chosen for analysis. However, it is generally agreed that the potential for liquefaction under the simultaneous action of both horizontal earthquake components is often higher than the liquefaction potential under the strongest horizontal component of earthquake base acceleration. Accordingly, saturated sand below the water table was modeled as a two-phase medium, with the porous granular solid and pore water as constituent materials. A new material model was introduced for the behavior of sand under cyclic bi-axial shear stresses. Results of analyses indicate the following: (1) the vertical component of base acceleration has minimal influence on the development and pattern of liquefaction, (2) interaction between the two horizontal components of shaking significantly influences the development and pattern of liquefaction, (3) increasing the amplitude of base acceleration in a one-directional analysis does not completely reproduce the major effects present in a two-dimensional analysis, and (4) interaction between the two horizontal components of shaking produces surface response spectra somewhat different from that of one-dimensional analysis.