ABSTRACT:

In order to study the behavior of sands under earthquake loading, the National Center for Research on Earthquake Engineering (NCREE) at Taiwan, has acquired a large laminated shear box with inside dimensions of 1.88 m × 1.88 m × 1.5 m to contain the soil specimens. The flexible shear box is composed of 15 layers of square frames made of aluminum alloy. Each individual frame is allowed to move freely in 2 axes on the horizontal plane while the shear box is subjected to a horizontal 2-dimensional shaking induced by the 5 m × 5 m shake table at NCREE. Thus, the effect of 2-dimensional ground motions on the soil behaviors can be studied. This shear box was specially designed so that torsional motion does not occur even with an eccentric mass center of sand in the box.

INTRODUCTION

The soil beneath level ground of an infinite extent under earthquake shaking are usually modeled as undergoing a simple shear loading condition. In order to study the soil behavior during earthquake, such as stress-strain relationship and liquefaction, small soil elements in the laboratory were tested using triaxial compression apparatus, simple shear devices, and torsional shear apparatus under regular sinusoidal cyclic loads. In these types of tests, the stress conditions and deformations in the soil elements are significantly affected by the boundary conditions, and the loading conditions are generally not the true field conditions due to the limitations of the loading devices. Therefore, large soil specimens have been placed on a shaking table that can reproduce the actual seismic ground shaking according to the earthquake recording under either 1 g or centrifugal conditions (e.g., De Alba, et al., 1976; Hushmand, et al., 1988). Thus, the soil behaviors, including liquefaction, under the true seismic conditions are able to observed and analyzed.

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