Characteristics of liquefaction strength of sandy soil deposits subjected to several overconsolidation histories and their long term effects on the strength

作者通过一系列试验研究了砂土在超固结应力历史作用下的液化强度特性，假定砂土堆积采用超载和降水方法作为液化对策。试验结果表明：1)超载处理的砂土地基的液化强度比采用脱水处理的砂土地基的液化强度提高幅度更大；2)液化强度的增加可以用超固结比和Ko值的关系式来表示，本文通过几组中空圆柱体扭转试验，研究了超固结度和超固结应力历史对液化强度的影响。在测试中观察到以下行为：1)在Oversoli…过程中的Ko值两种方法的应用顺序不同，影响程度也不同。2)在各向同性固结条件下，液化强度随固结时间的延长而增大，但比超固结比(OCR)_0略小。此外，当(OCR)_0=2时，液化强度没有增加。其中超固结过程中的最大围压作用于各向同性固结条件下的试件，时间较长。3)在Ko固结条件下，超固结过程中长时间施加最大围应力对试件的液化强度也没有提高。然而，在Ko固结条件下，当试件在长期固结过程中承受超固结的应力历史时，液化强度增加，强度的增加可用固结时间方程来表示，表明长期固结效应。较少

The authors had performed a series of tests to investigate characteristics of liquefaction strength of sand subjected to stress histories of overconsolidation, supposing that surcharge and dewatering methods were applied to sandy soil deposits as a countermeasure against liquefaction. It was clarified in the tests; 1) there is a possibility that the liquefaction strength increased more remarkably in the sandy soil deposits that were subjected to the surcharge method than to the dewatering method. 2) The increase in liquefaction strength can be expressed by an equation using overconsolidation ratio and Ko-value.In the present study, the Ko-value and the increase in the liquefaction strength were investigated in several series of hollow cylindrical torsion tests, where the specimens were subjected to both the surcharge and dewatering methods, and to stress histories of overconsolidation for a long time. The following behaviors were observed in the tests.1) The Ko-value during overconsoli … More dation was influenced by the order of applying of the two methods. However, the liquefaction strength depended on the Ko-value and overconsolidation ratio.2) The liquefaction strength increased as the consolidation time was long under isotropic consolidation condition, although the ratio of increase in the liquefaction strength was slightly smaller than that in the overconsolidation ratio, (OCR)_0, of 2. Moreover, In the case of (OCR)_0 = 2, the liquefaction strength did not increase, where the maximum confining stress during overconsolidation was applied to the specimen under isotropic consolidation condition for a long time.3) The liquefaction strength also did not increase under Ko-consolidation condition when the maximum confining stress was applied to the specimen for a long time during overconsolidation. However, the liquefaction strength increased under Ko-consolidation condition, when the specimen was subjected to stress histories of overconsolidation during long-term consolidation and the increase in the strength, which indicates a long-term consolidation effect, was expressed by an equation of the consolidation time. Less