Partially drained cyclic behaviour of granular fill material in triaxial condition

The dynamic responses of granular materials subjected to cyclic loading under partially drained condition were seldom investigated, though the partially drained condition is commonly existing for the granular materials that locate nearby the drainage boundaries. Besides, the prevalent studies mainly focus on the liquefaction behaviour of granular materials under high stress levels. In this study, a granular fill material was chosen as testing material. A series of partially drained cyclic triaxial tests was conducted with low level of cyclic loading and high cycle number that are commonly experienced in the geostructures of transportation projects. Note that the cyclic triaxial test under partially drained condition is a model test rather than an element test since the distribution of excess pore water pressure is not homogeneous inside the specimen. The test results show that cyclic loading induces the reconstruction effect on the microstructure of the specimen, thereby changing the trend between permeability and void ratio. Under partially drained condition, the granular fill material normally experiences a sudden decrease of stiffness and a quick increase in deformation during the first cycles of loading, followed by gradually decreasing excess pore water pressure and stabilizing deformation. Importantly, the deformation response of the material can be contributed by two items: (a) that caused by densification effect of applied cyclic loading and (b) that due to the dissipation of excess pore water pressure. Two linear relationships were established to correlate the deformations with excess pore water pressure and applied cyclic loading.