Dynamic Flow Characteristics of Liquefied Sand Under the Extrema Large Deformation in the Cyclic Torsional Shear Tests

Abstract

The dynamic flow deformation of liquefied saturated sand may cause serious damages to the ground and underground structures. However, to investigate the static fluid characteristics of the post-liquefied saturated sand, most studies on this problem have applied the cyclic loading to the saturated sand samples first, and then used the monotonic loading. The above test loading process is different from the actual stress state of soil in site. To investigate the dynamic flow characteristics of the liquefied saturated Nanjing sand under the cyclic loading, a series of undrained cyclic torsional shear tests are performed by using the hollow column torsional shear apparatus, with the largest shear strain up to 100%. At the same time, different effective confining pressure, initial shear stress and cyclic loading amplitude are loaded on the soil samples respectively. It is found that the soil sample has been in shear dilation state at the end of “zero effective stress” stage which is only determined by the excess pore pressure ratio. In other words, the response of excess pore pressure should be hysteretic to the shear dilation of the samples. It also proves that the initial shear stress should have the greatest influence on the relationship curves of the apparent viscosity-strain rate and the shear strain rate in the “zero effective stress” stage. Meanwhile, the dynamic apparent viscosity of sand in the “zero effective stress” stage under the cyclic loading is larger than the static apparent viscosity of post-liquefied sand when the shear strain rate reaches a relatively small value. Based on the test results, the dynamic apparent viscosity of liquefied sand should not be predicted by the empirical equation derived from the static fluid characteristics of the post-liquefied saturated sand.