PREDICTION OF LIQUEFACTION-INDUCED GROUND DEFORMATION

摘要

Prediction of liquefaction-induced ground deformation requires that the behavior of sand undergoing very low effective stress is understood experimentally. Previous 1-g model tests revealed a rate-dependent, or viscous, nature of liquefied sand. Since it was therein difficult to evaluate the rate-dependency more accurately, the present study carried out triaxial compression tests in a drained manner on Yurakucho sand with fines. The effective stress was maintained very low during shear by supplying high backpressure from outside. Creep tests in triaxial compression revealed that the shear stress consists of an inviscid frictional component and a rate-dependent component, and the study was focused on the latter. The test results demonstrated that the rate-dependent behavior of sand is similar to the Bingham model and that the effective stress of sand increases the magnitude of the viscous stress, enabling the rate-dependent deformation only under low effective stress. In contrast, the density of sand does not affect the rate-dependent nature significantly. The results of triaxial compression were supplemented by tests on triaxial extension as well as tests on special lightweight grains, where lower or null effective stresses were obtained. Finally, it is inferred that the cause of rate dependency is partly the vortex of pore fluid and partly the grain-to-grain collisions during shear deformation.