Experimental Study on the Directional Effect of Damage in Marble Under Different Impact Modes

The surrounding rock of a tunnel is subjected to cyclic impacts from different directions in tunnel engineering construction, resulting in directional damage to the rock mass. To investigate the impact direction effects on damage, a split Hopkinson pressure bar (SHPB) system was utilized to conduct cyclic impact tests on marble. The dynamic mechanical response of the marble was analyzed under different impact directions and loadings. Additionally, the P-wave velocity and pore distribution of damaged marble under different modes were obtained. The results showed that the P- wave velocity of marble decreased with the increasing impact times and loadings, while the porosity increased. The P-wave velocity of marble in Mode I was generally lower than that in Mode II, while the porosity was higher than that in Mode II. At an impact loading of 98 MPa, the porosity of marble subjected to three impacts was 3.21% and 1.98% under Modes I and II, respectively. The micropores showed a decreasing trend with impact times in Mode I, and the proportion of medium pores increased in both modes. In terms of dynamic properties, the dynamic peak strength and elastic modulus of marble declined with increasing damage. The degradation effect of Mode I on marble was significantly greater than that of Mode II, and it intensified with the increasing number of impacts and loadings. The difference in mechanical parameters and absorbed energy of marble under different impact modes increased with impact times and loadings. The energy absorption ratio of marble under Mode I was superior to that under Mode II. Additionally, a correction function was incorporated into the damage constitutive model to portray the compaction phase of marble. The improved model can accurately depict the mechanical response of marble under different modes. Finally, the damage anisotropy ratio (DAR) was defined based on P-wave velocity to characterize damage anisotropy, and the mechanism of damage anisotropy of marble under different impact modes was discussed. Dynamic compression tests were conducted on marble under different impact directions and loadings ultilizing an SHPB system.The directional effects of the P-wave velocity and pore characteristics of marble under different impact modes were obtained.The dynamic mechanical response of the marble and the differences in response under different impact modes were analyzed in depth.The damage anisotropic characteristics of marble under different impact modes were investigated, and the directional effect on the damage mechanism was discussed.