Mechanical properties and energy evolution of sandstone under unloading and freeze-thaw damage

Abstract

[Objective] To investigate the effects of freeze-thaw damage and excavation unloading damage on the mechanical properties of rock masses in cold regions. [Methods] Indoor mechanical tests were conducted on sandstone considering unloading and freeze-thaw damage factors in different order of action, and the mechanical properties and energy evolution laws of sandstone were analyzed. [Results] The result showed that the degradation of uniaxial compressive strength and elastic modulus of rock samples is most significant under the condition of “unloading freeze-thaw”. The fracture morphology gradually evolves from shear failure to tensile shear composite failure with increasing cycle times, and the main failure surface and tensile cracks are prone to develop along macroscopic freeze-thaw cracks. Damage increases the dissipated energy and its proportion during the process of rock sample failure, while reducing the energy storage limit. [Conclusion] The initial pore state of rock samples during freeze-thaw has a significant impact on the degree of degradation, and the feedback degree of early freeze-thaw damage to unloading damage is lower than that of early unloading damage to freeze-thaw damage. The damage mechanism of unloading and freeze-thaw on rock samples has a direct impact on the fracture morphology, proportion of dissipated energy, and storage and release of elastic energy of rock samples.

Keywords

sandstone / unloading damage / freeze-thaw damage / mechanical properties / energy evolution / influenaing factors / compressive strength