Abstract
Dynamic behavior of soil structures with a slope, such as fill dams, may be affected by initial shear stress, because soil under a sloping surface is subjected to shear stress prior to applying dynamic stress. The purpose of this study is to determine quantitatively the effects of initial shear stress on the dynamic behavior of the materials composed of those structures.
We performed dynamic triaxial tests on saturated Toyoura Sand applying static shear stresses prior to the application of dynamic stresses. The intensity of initial shear stress is determined by the static mobilized stress ratio MSR defined as MSR=(q/p')/(q/p') fail.; in which q=δ1'-δ3', p'=(δ1'+2δ3')/3 The sinusoidal dynamic load (f=1, 2, 4 Hz) is put through 30 cycles in an undrained condition.
The test results show that shear strain and pore pressure develop in different ways from those under the isotropic stress condition:(1) Plastic shear strain significantly increases in the first 10 cycles due to the anisotropic structure of the particles incurred by applying initial shear stress;(2), The development of positive or negative pore pressure and magnitude are determined by the anisotropic structure of the particles mentioned above;(3) Shear strain amplitude varies by the degree of the anisotropic structure and the magnitude of the pore pressure. Considering of the strong dependence of shear modulus G and damping ratio D on shear strain amplitude, it can be concluded that the dynamic deformation characteristic of sand is influenced considerably by initial shear stress. These effects of initial shear stress can be determined quantitatively by four factors; the static mobilized stress ratio MSR, shear stress amplitude qa, effective initial confining pressure ps' and number of cycles N.
