Study on strength and deformation characteristics of sandy mudstone based on triaxial unloading test

Abstract

To achieve the strength and deformation characteristics of sandy mudstone under the unloading condition, a triaxial unloading test was performed on a group of sandy mudstone taken from the diversion tunnel of a hydropower station. The results show that the stress-strain curve slope of sandy mudstone increases suddenly at the moment of unloading confining pressure, and there is no significant decline in the whole test. There is usually only a whole shear failure surface in the samples damaged under low initial unloading confining pressure while those damaged under high one develop tensile fracture. The introduction of semilog method helps to solve the problem that it’s difficult to get the peak intensity of sandy mudstone directly based on the variation characteristics of the stress-strain curve. From the initial stage of unloading to the damage of the samples, the reduced percentage of sandy mudstone deformation modulus is positively correlated with initial unloading confining pressure. The decrease rate of deformation modulus and increase rate of axial strain of sandy mudstone are both mutate under destructive confining pressure. The research results can provide an useful reference to research on the mechanical properties of similar soft rocks.