Experimental and numerical studies on failure behaviours of sandstones subject to freeze-thaw cycles

The freeze-thaw induced damage of rock affects the durability and serviceability of geo-structures, especially those constructed in the regions frequently impacted by climatic changes. A series of laboratory tests including P-wave velocity tests, freeze-thaw tests, uniaxial compression strength (UCS) tests and Brazilian tensile strength (BTS) tests are conducted to investigate the physical-mechanical properties and failure behaviours of Tasmanian sandstones subjected to various freeze-thaw cycles. It is observed that the P-wave velocity, BTS and UCS of the sandstone decrease as the number of freeze-thaw cycles increases, in which the decreasing rate from 0 to 20 freeze-thaw cycles was more pronounced than that from 20 to 40 and 40 to 60 freeze-thaw cycles. Moreover, it is found that the main failure mode of the sandstone changes from axial splitting to shearing along a single plane in the UCS tests and from central smooth fractures to a central zigzag fracture in the BTS tests with the number of freeze-thaw cycles increasing. Three-dimensional (3D) numerical modellings are then conducted using a self-developed 3D hybrid finite-discrete element method (HFDEM) parallelized on the basis of general-purpose graphic processing units (GPGPU) to further investigate the failure mechanisms of Tasmanian sandstones subjected to various freeze-thaw cycles in the UCS and BTS tests. The 3D numerical modellings agree very well with the experimental observations that the physical-mechanical parameters of the sandstone degrade with the increasing number of the freeze-thaw cycles. Moreover, the 3D numerical modellings reveal the deterioration and failure mechanisms of sandstones subjected to various freeze-thaw cycles. For the sandstone specimens without subjecting to freeze-thaw cycles, axial splitting is the main failure pattern while tensile and mixed-mode damages are the dominant failure mechanism in the UCS tests. For the sandstone subjecting to various freeze-thaw cycles, the increasing number of freeze-thaw cycles causes the macroscopic cracks to propagate, interact and coalesce in the shear behaviour resulting in the final shear fracture pattern in the UCS test. The 3D numerical modellings of the BTS test show that, although, for both the models with and without subjecting to freezing and thawing cycles, a central fracture is the eventual failure pattern, the failure surface becomes more zigzag as the number of freeze-thaw cycles increases.