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The pre-peak stress-strain properties of sedimentary softrocks were investigated by triaxial compression tests and large-amplitude cyclic loading tests extending triaxial compression and extension stress states. Axial strains were measured locally to a resolution of 0.0001%. Young's moduli Ev at quasi-elastic small axial strains of less than about 0.001% were evaluated at different isotropic and anisotropic stress states during those tests and isotropic compression tests. The Ev value increased rather uniquely with the vertical stress σv' while it decreased with large-amplitude cyclic straining, compared with those measured at isotropic stress states. A normalization method is proposed for the drained tangent Young's modulus Etan to exclude the effects of pressure change and damage by shearing on the Etan values by dividing each Etan value by the current Ev value. The Etan/Ev and q/qmax relationships are considered to have more general strain-nonlinear features than the relationships between the ratio of Etan to the initial elastic Young's modulus E0 and q/qmax.
softrock, triaxial test, stress-state dependency, damage, nonlinearity
Research associate, IIS, Univ. of Tokyo, Tokyo,
Professor, Univ. of Tokyo, Tokyo,
Researcher, Kawasakichisitu co., Tokyo,