A Study on Stability of Clay Deposits with Leaching during Earthquakes

本研究通过一系列的试验，阐明了有明粘土淋溶后的动力特性，并根据试验结果评价了粘土堆积体在地震作用下的土体结构稳定性。首先，提出了一种实验室模拟淋滤的方法，将蒸馏水渗入有利克海相粘土样品中三周，保持水力坡度为25。在此基础上，对有淋滤作用的粘土进行了阶段加载和固结试验，并进行了系列的动态变形和强度试验。在单次循环加载20次试验中，再次研究了循环加载后粘土的动强度、不排水抗剪强度和剪切模数折减率，以更清楚地反映淋滤对粘土动力特性的影响。此外，在多次循环加载的试验中，还研究了不排水抗剪强度和剪切模数折减率，以确定在严重加载条件下粘土试件是否转变为快速粘土。最后，在上述结果的基础上，进行了残余变形分析。研究发现：(1)由于淋溶作用，压缩系数增加，动态强度降低，动态变形特征没有改变。(2)在循环加载后，由于淋溶作用，未排水剪切强度和剪切模数降低。(3)剪切模数显著降低，但没有观察到未排水剪切茶中的速粘现象。即使在循环荷载作用下，剪切应变的倍增幅度达到10%。(4)残余变形分析表明，阿里亚克粘土堆积体中土体结构的稳定性明显丧失。

In this study, dynamic properties of Ariake clay with leaching were clarified by several series of tests and stability of earth structure on the clay deposit during earthquakes was estimated on the test results. Firstly, a method to simulate leaching in the laboratory was suggested to percolate distilled water into the specimen of Ariake marine clay for three weeks, keeping a hydraulic gradient of 25. And then several series of dynamic deformation and strength tests in the stage loading and consolidation tests were conducted on the clay with leaching. And the dynamic strength, and the undrained shear strength and reduction ratio of shear modulus after subjected to cyclic loading was again investigated in the tests on the clay subjected to single cyclic loading with 20 cycles, to appear the effects of leaching on the dynamic properties, more clearly. Furthermore, the undrained shear strength and reduction ratio of shear modulus were also investigated in the tests employing a cyclic loading with many cycles to confirm whether the clay specimen was changed into Quick clay under the severe loading condition. Lastly, a residual deformation analysis was performed, based on the results described above.The following behaviors were observed in the study.(1) The compressibility increased, the dynamic strength decreased and the dynamic deformation characteristics did not change, due to leaching.(2) The undrained shear strength and shear modulus decreased due to leaching, after the specimen was subjected to cyclic loading.(3) The shear modulus decreased remarkably, but a fenomenon of Quick clay was not observed in the undrained shear teas, even if the double amplitude of shear strain attained to 10% in the cyclic loading.(4) It was clarified in the residual deformation analysis that the stability of earth structure was lost remakably in Ariake clay deposits.