Investigation on the pore structure and dynamic strength degradation characteristics of weakly cemented sandstone under freeze-thaw cycles

In order to investigate the effect of freeze-thaw cycles on the pore structure and dynamic mechanical properties of weakly cemented sandstone, impact loading tests are conducted on samples under different initial freeze-thaw damage conditions. The pore structure evolution characteristics, freeze-thaw damage degradation law, dynamic mechanical behavior, and fragmentation characteristics of weakly cemented sandstone under freeze-thaw cycles are explored. The experimental results show that as the number of freeze-thaw cycles increases, the saturated water content of weakly cemented sandstone gradually increases, with values of 4.5%, 5.2%, 6.3%, and 7.6%, respectively. There is a good correlation between the number of freeze-thaw cycles and the saturated water content of weakly cemented sandstone. The freeze-thaw damage has a significant impact on the expansion of micro pores and mesopores inside weakly cemented sandstone. The impact on the expansion of macroscopic cracks is relatively small. As the number of freeze-thaw cycles increases, the dynamic strength of weakly cemented sandstone specimens gradually decreases, with values of 87.85 MPa, 73.37 MPa, 53.63 MPa, and 33.23 MPa, respectively. Compared to the weak cemented sandstone specimens without freeze-thaw treatment, the dynamic strength decreased by 16.48%, 38.95%, and 62.17%, respectively. The energy absorption rate per unit volume and the fractal dimension of crushing mass shows a gradually increasing trend with the increase of freeze-thaw cycles. The average fragment size shows a gradually decreasing trend.