Experimental study on mechanical characteristics and damage degradation mechanism of conglomerate under drying-wetting cycles

To study the mechanical characteristics and damage degradation mechanism of conglomerate samples under drying-wetting cycles, uniaxial compression tests were carried out under different drying-wetting cycles (0~4 times, drying-wetting cycles period of 10 d). The strength, deformation and failure characteristics of samples were analyzed, and the deterioration effect of the mechanical properties of the conglomerate samples was explored. The damage degradation model of conglomerate samples during drying-wetting cycles and before and after drying-wetting cycles was established, and the damage degradation mechanism of conglomerate samples under drying-wetting cycles was analyzed from the aspects of meso-structure and component changes. The results show that (1) the mechanical properties of conglomerate samples decrease with the increase of drying-wetting cycles, and the uniaxial compression stress-strain curve changes from steep decline to ductile decline modes in the post-peak stage. Also, the plastic failure degree of conglomerate samples increases, and the failure mode of samples changes from tensile failure to shear ejection failure. (2) With the increase of the number of drying-wetting cycles, the formation time of deformation localization zone of conglomerate samples is advanced and the number of localization zones increases, and the ringing count of acoustic emission of samples increases sharply. The decrease of elastic energy density in the pre-peak stage leads to the decrease of peak stress of samples, and the increase of energy density in the post-peak stage causes the increase of crushing degree of samples. (3) In the process of drying-wetting cycles, kaolinite, illite and other minerals are dissolved, and the internal defects of the conglomerate samples continued to expand and shrink. Compared with the the XH–0d group samples, the average porosity at the fracture surface increased respectively by 6.96%, 14.41%, 24.00% and 48.10%. With the increase of the number of drying-wetting cycles, the damage of the conglomerate samples increases, and the effective bearing structure area decreases, which ultimately contributes to the deterioration of its mechanical properties. The research results can provide some reference for ensuring the safe mining of coal seams.