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

为了采取适当的措施减轻因土壤液化引起的地震破坏，对地基可能发生的变形进行精确的评估是十分必要的。因此，建立一种较好的预测土壤液化变形的方法是迫切需要的。对土在液化后的变形特性进行了试验研究。后液化状态通过两种方式形成：一种是冲击瞬时液化，另一种是循环振动液化。通过观察土粒的运动来监测土骨架的变形，并探讨土粒的运动对土骨架变形的影响。为阐明液化土的强度特性，还进行了扭剪试验。所得结果如下：1)水平地基时，土体骨架被瞬时液化完全破坏。因此，土壤颗粒在液化后处于悬浮状态。其悬浮状态的持续时间取决于土粒下移直至土骨架重建所需的时间。(2)当地面横向边界可移动时，水与悬浮土颗粒的混合物可根据边界运动进行横向移动。在这种情况下，土壤颗粒的运动比水的运动延迟，因为土壤颗粒的质量比水的质量大。这种延迟引起骨架结构的重建，因此容易触发剪胀引起的超孔隙水压力的降低。(3)循环震动液化时，由于剪应力方向逆转和地面变形的双重作用，超孔隙水压力循环上升下降。(4)在孔压保持较高的情况下，地基液化导致路堤沉降。结果表明，将液化层视为黏性液体，可以分析路基的沉降过程。在循环液化状态下，孔隙水压力升高时，在短时间内引起沉降。而总结算金额是每次结算的累加。5)对于沉降时程，采用该算法计算的路堤与振动台试验结果吻合较好。综上所述，液化后的地面即使在有限的时间内也表现出液态。同时也说明了液体状态的持续时间一直持续到骨架结构重建。骨架结构的重建是由土壤颗粒的沉降或水与土壤颗粒的混合物的运动来完成的。这意味着在分析液化后土体变形时，需要引入固液混合物的动力学。少

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