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Experimental investigation on dynamic mechanical properties and fracture evolution behavior of the underground openings with excavation damaged zones

The existence of excavation damaged zone (EDZ) generally influences the stability and safety of the underground openings. To investigate the influence of EDZ on the stability of underground excavation under dynamic stress disturbances, underground excavations with EDZs are represented by holed rock specimens with damage zones. The fracture evolution and dynamic mechanical properties of damaged holed rock specimens under dynamic loads are investigated by using the improved Split Hopkinson Pressure Bar (SHPB). The results have shown that the stress-strain curve of the rock specimens with damage zones is divided into pre-peak and post-peak stages, without compaction and elastic deformation stages. The dynamic strength, peak deformation moduli, and crack initiation stress decrease while the strain rate, absorbed energy, and failure time of holed specimens increase with increasing damage around circular holes. The failure of the holed rock specimens always start from circular holes, and specimens without or with minor damage exhibit overall tensile-shear failure. However, the failure of rock specimens with a greater damage condition mainly appears within damage zones around circular holes in the form of spalling or compression-shear failure, and the failure zone increases with increasing damage of surrounding rocks. The failure around and away from circular holes of specimens without or with minor damage is respectively characterized by intergranular and transgranular cracks. The results of the present study provide implications to the disaster prevention and support design of underground openings with EDZ.