A STUDY ON MOVEMENT OF SOIL PARTICLES AND DEFORMATION OF SOIL UNDER POST LIQUEFACTION STATE

点击翻译按钮获取中文摘要

In order to mitigate seismic damage due to soil liquefaction by proper measure, precise evaluation of possible deformation of ground is essential. So, it has been desired to establish a better method for predicting soil deformation due to soil liquefaction. Deformation characteristics of soil during post liquefaction state were investigated experimentally in this research. Post liquefaction state was made by two ways : one is instantaneous liquefaction by shock, and the other is by cyclic shaking. Deformation of soil skeleton was monitored by observing the movements of soil particles and the effects of these movements to soil deformation were examined. The torsional shear tests were also conducted to clarify the characteristics of strength of liquefied soil. The obtained results are as follows.1)In the case of horizontal ground, soil skeleton is completely destroyed by instantaneous liquefaction. So, the soil particle becomes suspended state after liquefaction. The continuing time of t … More his suspended state is governed by the necessary time for the soil particles move down until the soil skeleton is rebuild.2)When the lateral boundary of a ground is movable, mixture of water and suspended soil particles can move laterally in accord with boundary movement. In such a case, movement of soil particles is delayed than the movement of water, because the mass of a soil particle is larger than the one of water. This delay causes reconstruction of skeleton structure, so the reduction of excess pore water pressure due to the dilatancy is easily triggered.3)In case of the liquefaction by a cyclic shaking, the excess pore water pressure cyclically rises up and drops down, because of both reversing of shear stress direction and ground deformation.4)Settlement of an embankment due to the liquefaction of foundation ground progresses while the pore pressure is kept to be high. It was shown that the settlement process of such embankment can be analyzed by treating the liquefied layer as viscous liquid. In case the liquefied state is cyclically brought about, the settlement is brought about during the short periods while the pore water pressure is raised high. And the total settlement amount is an accumulation of each settlement.5)The calculated result of embankment by using this algorithm agrees well with results of shaking table tests even for the time history of settlement.Summarizing the above results, it is found that the liquefied ground behaves like liquid even though it keeps for limited time. It is also clarified that the duration of liquid-like state continued until the skeleton structure is reconstructed. And the reconstruction of skeleton structure is made by the sedimentation of soil particles or the movement of mixture of water and soil particles. This means that it is needed to introduce dynamics of the solid-liquid mixture in the analysis of soil deformation in post liquefaction state. Less