THE STRENGTH AND DEFORMATION CHARACTERISTICS OF CLAY SUBJECTED TO CYCLIC SHEAR STRESS

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In this paper, strength and deformation characteristics of clay (Kanto loam) which has undegone cyclic shear is investigated by cyclic triaxial tests. In the tests, the effect of the overconsolidation ratio on static and dynamic strength was examined under Ko overconsolidation condition created by loading pre-load and Ko normal consolidation. The residual pore water pressure, volumetric change and undrained shear characteristics were examined using the specimens which did not break under cyclic shear. The results which were obtained from this study are summarized as follows.1.As for Kanto loam under isotropic consolidation, Ko normal consolidation or Ko overconsolidation, the line of undrained cyclic shear breaking overlaps the line of static undrained shear breaking.2.Unlike its effect on static strength, pre-loading does not induce a significant increase of dynamic strength and ultimate yield strength defined by axial strain and the number of repeitions of applied deviator stress. In … More other words, dynamic strength can not be expected to increase as much as static strength with the same pre-loading. The ultimate yield strength and its corresponding static strength decrease as the overconsolidation ratio increases. Therefore, we cannot expect the dynamic strength to increase as much as the static strength increases with pre-loading.3.The relationship between effective stress increase and volumetric change obtained by residual water pressure can be expressed by a particular type of straight line, irrespective of overconsolidation ratios. A similar relationship in regard to clay has been reported by Matsui and Yasuhara.4.The increase of strength due to re-consolidation after cyclic loading is proportional to the increase of effective pressure due re-consolidation in the specimens under Ko normal consolidation. However, the strength of the specimens under Ko overconsolidation does not increase even though the specimens are also re-consolidated. The soil structure change due to cyclic loading nulified the increase of strength due to re-consolidation.5.The lager the cyclic loading stress is, the more the deformation modulus E50 of re-consolidated specimens decreases, even though the strength increases by re-consolidation after cyclic loading. The larger the OCR is and the more the specimens are affected by a reversal of principal stress, the more the decrease of strength and deformation modulus is significant. Less