Experimental research of influences of freeze-thaw cycles and confining pressure on physical-mechanical characteristics of rocks

The freeze-thaw cycling experiment was conducted for water-saturated sandstone under an open system to re- cord the freeze-thaw deterioration process and failure characteristic of rock. And then the mechanical properties experi- ment with four kinds of confining pressures was carried out for sandstone on different freeze-thaw cycles (0,5,10,20, 40 times). Subsequently,the influence law of freeze-thaw cycles and confining pressure on the physical and mechani- cal properties of rock was analyzed systematically. The result shows that the primary modes of freeze-thaw damage dete- rioration for sandstone are spalling mode,crack mode,shedding mode and fracture mode. With the increase of freeze- thaw cycles,the quality and density of rock samples present the trend of increasing at first and then decreasing,while the speed of the longitudinal wave decreases continuously. With the increase of confining pressure and the number of freeze-thaw cycles,the compaction property is enhanced gradually, the peak strain increases constantly, the plastic yield segment is becoming obviously,and the reduction rate of residual strength decreases,exhibiting the failure mode of enhanced ductility and weakened brittleness. While the elastic modulus,compressive strength and residual strength increase obviously with the increase of confining pressure, and decrease with the increase of freeze-thaw cycles. Through the nonlinear evolution of meso-structural damage,the rock displays the variation of macroscopic mechanical properties.