EFFECTS OF STRESS HISTORY DUE TO UNSATURATION AND DRAINAGE CONDITION ON SHEAR PROPERTIES OF UNSATURATED COHESIVE SOIL

 HIROFUMI TOYOTA , NAOKI SAKAI  and TOMOYOSHI NISHIMURA 

ABSTRACT: Several studies have concluded that the effect of matric suction on the shear strength of unsaturated soil is very important. However, little attention is given to the stress history due to unsaturation and drainage condition in the arrangement of these experimental results. This paper attempts to show the relationship between shear properties and matric suction under a specified stress history and drainage condition. In this study, an unsaturated specimen is set up by dehydrating the normally consolidated soil with controlled matric suction to a specified stress history. Triaxial apparatus and hollow cylindrical torsional shear apparatus are employed to examine the effects of stress history and drainage condition, respectively. 'Through systematic experiments, the effects of stress history and drainage condition on the stress-strain relationship are clarified. The increase in shear strength by matric suction which is measured at the point of maximum shear stress is observed to be independent of stress history and drainage condition. However, in strain softening behavior it was found that the ultimate strength is independent of matric suction and traces a unique line which is parallel to the critical state line on the p_net - q plane.

Key words: cohesive soil, shear strength, stress history, torsional shear, triaxial test, unsaturated soil (IGC: D6)