Effect of Prestress and Freeze-Thaw Cycles on Physico-mechanical Properties of Sandstone

In order to study the effect of seasonal freezing and thawing on rocks under in-situ stress, taking the sandstone on the bank slope of the Three Gorges Reservoir Area as the research object, a device which can carry out prestressed loading on standard samples is designed. The physical and mechanical properties of sandstone under different prestress levels and freeze-thaw cycles are tested. The variation rules of sandstone mass, porosity, wave velocity and compressive strength under prestress and freeze-thaw cycles are analyzed, and the influence mechanism of prestress and frost heaving force on rock mechanical properties is discussed from the perspective of stress distribution around pores. The results show that the mass loss rate, pore growth rate and longitudinal wave velocity attenuation rate of sandstone are directly proportional to the number of freeze-thaw cycles, and the application of prestress will significantly improve the above damage caused by freeze-thaw cycles; The uniaxial and triaxial compressive strength of sandstone under freezing-thawing increases sharply first and then tends to be stable with the increase of prestress. The frost resistance coefficient of sandstone with prestress can reach more than 75%. The prestress in the range of 0 ~ 3MPa can improve the frost resistance of sandstone more effectively, and the existence of Confining pressure can also weaken the deterioration effect of the freeze-thaw cycle on sandstone strength; Prestress changes the stress distribution of the pores in the sandstone and forms a compressive stress zone on both sides of the pores, which can effectively resist the tangential tensile stress formed by frost heave and inhibit the damage of freeze-thaw cycle to the sandstone. The research results can deepen the understanding of the law and mechanism of sandstone damage and deterioration under freeze-thaw cycles, and provide basis for rock mass engineering construction in cold regions.