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

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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