Effect of multidirectional earthquake loadingon seismic compression of sand

Dynamic simple shear tests on different types of sand under multidirectional earthquake loading are simulated by means of the finite element method. The reduced order bounding surface model is employed and its parameters are determined based on the results obtained from laboratory dynamic simple shear tests. 148 groups of ground motions with multi-components from far and/or near fields of moderate and/or strong earthquake events at different site conditions are used as input motions for strain controlled and stress controlled dynamic simple shear tests. Effect of multidirectional earthquake loading on seismic compression of sand for different earthquake magnitudes site-to-source distances and properties of sand is studied. The results show that the ratio of vertical strain induced by multi-components of seismic loading and that induced by one component of seismic loading are greatly associated with earthquake magnitude, site-to-source distance and properties of sand, the ratio of vertical strain increases with the increasing earthquake magnitude and relative density of sand, and decreases with the increasing site-to-source distances. Great limitation exists in the method considering the effect of multidirectional earthquake loading on seismic compression proposed by Pyke et al (1975) due to its lack of considering the effect of characteristics of seismic loading and properties of sand. Also, the ratios obtained from stress controlled and strain controlled simple shear tests are greatly different and the mean ratios from the former are larger than those from the latter.