Effect of Loading Condition on Liqefaction Strength of Saturated Sand

Abstract

Liquefaction strength is, obtained by means of a cyclic triaxial test in the engineering practice. This loading procedure of a cyclic triaxial test is equivalent to the shear stress condition acting on the horizontal plane in the ground during an earthquake. This method has a disadvantage, however, that effective mean stress changes. When simulating the behavior of the level ground, the cyclic shear stress must be applied while inhibiting lateral deformation as a torsional shear test. These tests were performed. The following conclusions were obtained from a series of test result.

• (1) The result of these laboratory tests shows that the liquefaction strength defined as 7.5% shear strain in double amplitude is generally agreement between triaxial and torsional test.

• (2) The stress condition appears to affect the behavior of excess pore pressure and shear strain up to liquefaction strength. In particular, the behavior of the cyclic triaxial tests is different stress condition between in-situ and laboratory.

• (3) It was noteworthy that the minimum cyclic shear strength was observed at cyclic triaxial test that is ordinary used in small shear strain up to 7.5% in double amplitude. The main reason for this behavior is that the effective confining pressure is decrease, when the cyclic axial stress direction is extension.