Dynamic Mechanical Behavior and Numerical Simulation of an Ancient Underground Rock Mass under Impact Loading

To study the dynamic mechanical properties of tuff under different environmental conditions, the tuff from an ancient quarry in Shepan Island was prepared. The impact damage to the rock was tested using a triaxial dynamic impact mechanical testing system (TDIMTS) with different ground stresses, temperatures, and groundwater pressures. The time-strain relationship, dynamic stress-strain relationship, energy dissipation law, energy-peak strain relationship, and the impact damage pattern of the tuff specimens under impact air pressures were investigated. The TDIMTS experiment on ancient underground rock mass under impact loading was also simulated using the finite element analysis software LS-DYNA based on the Holmquist-Johnson-Cook (HJC) material model. The dynamic failure process, failure pattern and peak stress of tuff specimen were calculated. The simulation results obtained using the above methods were in good agreement with the experimental results. The results of the dynamic experiment show that with the same local stress, groundwater pressure, and temperature, the damage to the tuff specimens caused by blasting and quarrying disturbances gradually increases as the impact pressure increases. Under the same local stress, groundwater pressure, and temperature, the energy required to rupture the tuffs in ancient underground caverns is relatively small if the impact pressure is low accordingly, but as the impact pressure increases, the damage to the tuff caused by quarrying disturbance gradually increases. The damage gradually increases and the degree of damage to the tuff and the strain energy exhibit asymptotic growth when the tuff specimens are subjected to the greater strain energy, increasing the degree of rupturing of the tuff. In addition, the average crushing size decreases with increasing strain energy. By comparing the simulation results with the experimental results, it was found that the HJC model reflected the dynamic impact performance of tuff specimen, and the simulation results showed an evident strain rate effect. These results of this study can offer some guidance and theoretical support for the stability evaluation, protection, and safe operation of the ancient underground caverns in future.