Mechanism of cyclic softening of non-plastic silt and its countermeasures

横向流动是在地震期间和地震后由于液化而发生的大规模横向地面运动。推断出横向流动。在地震灾害中对建筑物的基础和生命线造成最大的破坏。为了明确淤泥的液化脆弱性，我们需要一种根据地面液化预测变形的方法。本研究提出了粉质土液化变形的预测方法，并提出了减少粉质土液化后变形破坏的对策。研究结果总结如下：1)循环后三轴试验结果表明，随着超孔隙水压力的升高，淤泥的刚度逐渐减小。然而，当超过超孔隙水压力的0.8时，该刚度迅速下降。采用砂石排水作为对策，将超孔隙水压力控制在0.8以下，可显著减小地震后地面变形。2)采用超孔隙水压力模型预测液化后变形模量的变化。在模型试验中，将其纳入了粉土地基变形预测有限元程序中。采用本文提出的有限元计算规范，得到了斜坡粉土地基的实际变形与预测变形吻合较好的结果。3)在斜坡粉土地基1G模型试验中，粉土液化引起的变形随地基坡度的不同而不同：严重斜坡时，侧流异常；坡度平缓时，竖向变形占主导地位。对比液化前后粉土与砂土的作用，发现液化过程中粉土的变形有明显的延迟，但液化后砂土的位移量较大。而且，最终的位移量与砂土的位移量几乎相同。这些结果强调，在地震过程中，不仅要注意砂土的液化后变形，而且要注意粉土的液化后变形。4)在常规砂石排水的基础上，采用胎屑排水减少粉土地基液化后变形。模型试验结果表明，胎屑排水法不仅可以减小侧向位移，而且可以减小竖向位移。这些影响几乎与在相同条件下安装砾石排水管的情况相同。这表明，轮胎片排水法可以作为一种经济的措施来防止液化引起的淤泥变形。少

Lateral flow is a large lateral movement of the ground that occurs horizontally as a result of liquefaction during and after earthquakes. Lateral flow is inferred. to cause most damage to foundations of structures and lifelines during earthquake-induced disasters. For clarifying vulnerabilities to liquefaction of silts, we require a method of forecasting the deformation according to ground liquefaction. This study proposes a method for predicting the liquefaction-induced deformation of silty soil and proposing the countermeasure to reduce damage due to post-liquefaction deformation.Results of the present study are summarized as follows :1)Results from post-cyclic triaxial tests on silt indicate that stiffness decreases gradually as excess pore water pressure rises. However, that rigidity decreases rapidly when a ratio of 0.8 of the excess pore water pressure is exceeded. Ground deformation after earthquakes can be decreased considerably if the excess pore water pressure is maintained b … More elow 0.8 using gravel drains as a countermeasure.2)The excess pore water pressure model was adopted to predict changes in the deformation modulus after liquefaction. It was incorporated into the FEM code for predicting silt ground deformation in model tests. Using the proposed FEM code, we obtained good agreement between observed and predicted deformation of sloping silt ground.3)In 1G model tests on sloping silt ground, deformation attributable to the liquefaction of silty soil differs depending on the ground slope : lateral flow is exceptional when the ground is severely sloping ; vertical deformation is dominant when the slope is gentle. Moreover, comparison of the actions of silt with that in sand before and after liquefaction showed remarkable delay of silt deformation in the transformation, but the amount of sand displacement is greater immediately after liquefaction. Moreover, the final amount of displacement is nearly identical to that of sand. These results emphasize that, during earthquakes, attention should be given to post-liquefaction deformation of silt as well as that of sand.4)The tire-chip drain was adopted for reducing post-liquefaction deformation of silt ground along with the conventionally used gravel drain. Results of model tests demonstrated that the tire-chip drain method is available for reducing not only lateral displacement but also vertical displacement. These effects are almost identical to those of the cases in which gravel drains are installed in the same condition. This suggests that the tire-chip drain method can be an economical countermeasure for preventing liquefaction-induced silt deformation. Less