An investigation on effects of countermeasures against liquefaction of sand deposits with structures

通过离心模型试验，研究了地下构造和地表构造对砂土液化的影响。对5类模型进行了模型试验；一种没有对策，四种有对策；具有或不具有排水能力的板桩墙，板桩墙顶部系杆和砾石排水管。本研究得出以下结论：对于具有地下结构的地基土，当结构下超孔隙压力达到一定阈值时，地基土会发生向上运动。为了防止孔隙向上运动，应尽量使超孔隙压力低于该阈值。结构的加速度响应在很大程度上取决于地基土中产生的超孔隙压力。在所有情况下，输入运动的早期阶段的加速度响应是相似的，但随后的响应对于不同类型的对抗是不同的。在无排水情况下，结构的加速度随超孔隙压力的产生而减小。另一方面，在排水情况下，结构的加速度增加。油罐、路堤等地面构筑物的沉降有两个原因；下面的沙子由于固结而被压缩，另一个是沙子的横向运动。横向运动的增加引起结构总沉降的增加，抑制横向扩展是必要的。

Centrifuge model tests are carried out to study the effect of various countermeasures against liquefaction of sand deposits with an undergrond structure and a structure on surface. Model tests are conduced on five types of models ; one without any countermeasures and four with countermeasures ; sheet pile walls with or without drainage capability, sheet pile walls of which tops are tied with rods and gravel drains.Following conludsions are drawn from this study.1.For foundation soil with an underground structure, upward movements of it take place when excess pore pressure beneath the structure reaches a threshold value. In countermeasures to prevent the upward movement, an attempt should be made to keep the excess pore pressure lower than this threshold.2.Responses of acceleration of structures depend very much on the excess pore pressures generated in foundation soil. The acceleration responses at the very early stages of input motons are similar for all the cases, but the subsequcnt responsese differ for different types of countermeasure. For the cases without drainage, the acceliration of structure decreases with the generation of excess pore pressure. On the other hand, for the cases with drainage, the acceleration of structure increase.3.Settlements of structures on a ground surface like oil tank and embankment arise from two reasons ; the compression of sand beneath due to consolidation and the other the lateral movement of hte sand. Increase of lateral movement gives rise to an increase in total settlements of the structure, suppression of lateral spreading is necessary.