A Study on Stability of Clay Deposits with Leaching during Earthquakes

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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.