The effect of freezing and thawing cycles on the mechanical properties and slope stability of the waste dump

To investigate the shear strength evolution of soil-rock material in waste dump induced by freezing and thawing cycle (FTC), the shear tests are conducted by a self-developed direct shear apparatus, and the effect of FTCs on the shear strength degradation curve of soil-rock material is obtained. Furthermore, the inner microstructure of soil-rock material induced by FTC is analyzed by computer topography (CT)scanning testing.Finally, the stability of waste dump after and before freezing and thawing is compared. The results show that the shear and displacement curves of soil-rock material present strain softening during low normal loading pressure. However, the shear and displacement curve development trend changes from strain softening to strain hardening, and the shear dilatancy happens during loading process. As the FTCs increase, the strain hardening behavior becomes more obvious and the shear dilatancy effect is weakened. In addition, both the cohesion and friction angles decrease as the FTCs increase. When the number of FTC increases to 15, the decrement of cohesion and friction angle is 18.45 % and 9.42 %, respectively. The reason is mainly attributed to the dislocation and regroup of fine rock particles induced by freezing crack.The change in porosity of soil-rock material mainly happens within the initial 5 freezing and thawing cycles. The safety coefficient decrement of waste dump is approximately 7.6 % as the FTCs increase from 0 to 15. The results can provide guidance for waste dump in cold regions.