Impacts of Excess Pore-Water Pressure on Dynamic Properties of Saturated Clay

Abstract

For equivalent linear and nonlinear site response analysis, both shear modulus and damping ratio are critical input factors. The elastic modulus and damping ratio of saturated soft clay are usually determined using cyclic triaxial tests. However, the dynamic behaviors of saturated clay are affected by excess pore-water pressure induced under cyclic loading. Therefore, the evolutions of both elastic modulus and damping ratio, under cyclic triaxial tests with and without drainage, are the main focus of the investigation. Two types of cyclic triaxial tests were performed, in which the primary distinction is whether the excess pore-water pressure caused by the previous stage’s cyclic loading is released prior to the application of the next stage’s cyclic loading. The impacts of several parameters, such as effective confining pressure and excess pore-water pressure, were investigated. As the effective confining pressure increases, so does the maximum elastic modulus. Excess pore-water pressure has a significant effect on maximum elastic modulus. The maximum elastic modulus under the condition with drainage increases linearly with that obtained without drainage. Besides that, the variations of normalized elastic modulus with effective confining pressure are negligible under the condition without drainage, while the impact of effective confining pressure is more apparent in the condition of drainage. Nevertheless, the influence of effective confining pressure on the damping ratio can be ignored over the range of axial strain. The damping ratio without drainage is higher than that obtained under the condition with drainage. Based on that, the variation of normalized elastic modulus versus axial strain can be depicted by an empirical function, while the evolution of the damping ratio is represented by a hyperbolic model.