Characteristics And Mechanism of Vibratory Densification of Sand And Role of Acceleration

Abstract

Vertical vibration tests with a rigid mold as well as dynamic and cyclic simple shear tests were conducted on sand to investigate the characteristics and mechanism of densification. Vertical acceleration was applied to the sample in the vertical vibration tests, but the dynamic stress was very small relative to the confining stress. Dynamic and cyclic simple shear tests were conducted by using the same simple shear apparatus. Both dynamic shear stress and horizontal acceleration were given to the sample in the dynamic simple shear tests. Cyclic simple shear tests were conducted under the following two kinds of conditions to investigate the role of acceleration in the densification of sand by vibration. (1) Only the cyclic shear stress, whose amplitude was equal to that of the dynamic shear stress, was given to the sample by stress controlling. (2) The shear strain amplitudes, which were equal to those in the dynamic simple shear tests, were given to the sample by strain controlling. From all these results, it was recognized that vibratory acceleration participated in the densification of sand by vibration in two ways. One was as an average dynamic stress and the other was as body force applied directly to each grain of sand. When dynamic shear stress became the dominant factor, the body force and the damping resistance in a sample had respective influences on the densification of sand to a degree that was not negligible. Moreover, the relationship between the volume change and the shear strain was not significantly affected by the values of overburden pressures and accelerations or the randomness of shear strain amplitudes.