Cyclic torsional shear loading tests on the extremely large post-liquefaction flow deformation of saturated Nanjing sand

To investigate the post-liquefaction flow deformation of saturated Nanjing sand mostly composed of flaky grains, the hollow column torsional shear apparatus is used to simulate the loading states of the soils in the site with large liquefaction-induced lateral deformation. The results show that the resistance of Nanjing sand against the liquefaction and the post-liquefaction accumulation deformation increase with the effective confining pressure, and they also have increasing tendency under the same effective confining pressure. Without the initial shear forces, the post-liquefaction deformation of saturated Nanjing sand is mainly the cyclic liquefaction-induced deformation, and single direction accumulated flow deformation is also found, which also increases with the cyclic loading. The effect of the initial shear forces should be divided into three stages. In the first stage, the resistance of Nanjing sand against the liquefaction and the post-liquefaction accumulation deformation decrease severely with the increasing initial shear forces, and the soil samples are mainly damaged by the large liquefaction-induced flow deformation. However, when the initial shear forces are close to the cyclic shear forces, the resistance of Nanjing sand against the liquefaction and the post-liquefaction accumulation deformation increase quickly with the increasing initial shear forces, and the soil samples are mainly damaged by the large liquefaction-induced flow deformation in this stage. When the initial shear force is large enough, the saturated Nanjing sand is not liquefied until the single direction accumulated deformation reaches 30%, which proves that the large deformation of the saturated Nanjing sand is mainly caused by the large plastic deformation. Meanwhile, the large post-liquefaction deformation of saturated Nanjing sand is also different from that of the Toyoura sand mainly composed of round grains.