Cyclic freeze–thaw induced stiffness anisotropy of sandy silt under all-round and unidirectional freezing modes

Abstract

The stiffness anisotropy of soil is a critical factor that influences the deformation characteristics of soil in landform evolution, geological disaster mitigation and engineering applications. However, the effects of freeze–thaw cycles on the stiffness anisotropy of soil have not been clearly understood. In this study, a new thermal boundary-controlled triaxial testing system equipped with bender elements is developed to investigate the effects of cyclic freeze–thaw on the stiffness of a sandy silt under both unidirectional and all-round freezing modes. It is revealed that under all-round freeze–thaw cycles, the shear wave velocity in the horizontal and vertical planes undergoes a continuous increase of 14% and 8%, respectively. In contrast, unidirectional freeze–thaw leads to a non-monotonic evolution of shear wave velocity, eventually resulting in a 3% reduction in the horizontal plane and a 16% reduction in the vertical plane after 10 freeze–thaw cycles. The increase in shear stiffness anisotropy of the sandy silt after freeze–thaw cycles is more significant in the unidirectional freeze–thaw condition (from 1.11 to 1.49) compared with the all-round freeze–thaw condition (from 1.13 to 1.19). This study illustrates the significance of unidirectional freeze–thaw in the evolution of mechanical anisotropy of soils in cold regions.