Study on Ground Displacement in Liquefiable soil by Shaking Table Tests

摘要

Liquefaction is one of the important reasons in earthquake damages. The response and damage for the foundations and underground structures are dominated by soil deformation in general and in this case, displacements in liquefiable soil layer play more important role than acceleration. Generally, liquefaction displacement can be divided into two types. One is permanent displacements including the lateral spreading and the vertical settlements, and the other is the dynamic cyclic displacements related with the displacement spectra. Many research is performed for the former problem and for the later problem, however, rare study is conducted. The shaking table test on effect of liquefaction on the cyclic displacement of the soil layer is performed. Taking the dry sand model tests as a datum, the relationship between the pore water pressure and the ground accelerations as well as the relationship between the pore water pressure and the ground displacement for the liquefiable saturated sand model are attained. The testing results indicate that the liquefaction flits the high frequency parts of the incident waves and reduce the ground acceleration amplitude. Meanwhile, the liquefaction enlarges the cyclic displacement and strain in the liquefied soil layer. For the cyclic deformation, the strain in the liquefied soil layer already reaches 1%-5%, i.e., the large deformation scope, and much larger that in the dry sand layer. During the water pressure range of 0.4-0.8, the cyclic displacement of the liquefiable soils increases significantly and reaches the maximum when pore pressure is about 0.8 other than 1.0. When the liquefaction occurs, the strain in the deep parts of the soil layer is larger than that in shallow parts. As a result, the liquefied soils reduce the rigid superstructures while amplify the cyclic displacements greatly which easily cause the damages of foundations and underground structures, especially for the interface parts between the liquefied soil layer and the below non-liquefied soil layer.