Experimental study on multi-scale damage and deterioration mechanism of carbonaceous slate under freeze-thaw cycles

This study investigates the macro and micro multi-scale damage effects of freeze-thaw cycles and confining pressure on slate tunnel rock in cold regions. Herein, carbonaceous slate excavated from a tunnel under construction in the Qinghai-Tibet plateau was selected as the research object, and the following conclusions were drawn from the experimental research: (1) the signal peaks of the T2 spectrum of the slate specimens mainly presented a two-peak shape, and under the action of freeze-thaw cycles, the pore structure expanded to large pore size and the pore size tends to be homogeneous, indicating that the third peak of extra-large pore size appeared intermittently; (2) the porosity of slate will reach a critical value under the action of freeze-thaw cycles, and when the porosity of rock block with weak structure increases to the critical porosity, it will spall off and form local macro damage; (3) the coupling effect of freeze-thaw and confining pressure made the failure of the slate gradually transform from brittle to ductile, revealing the deterioration law of mechanical properties of slate induced by freeze-thaw cycles and the weakening effect of confining pressure on the loss of mechanical properties of slate induced by freeze-thaw; (4) the freeze-thaw loading damage model was established based on the macro and micro viewpoints, revealing the damage expansion law of freeze-thawed slate under loading and the weakening effect of confining pressure on the freeze-thaw damage of slate.