Spallation damage mechanism of prefabricated elliptical holes by different transient incident waves in sandstones

Abstract

The predictability of the failure process of underground rock mass located adjacent to a cavity is a key challenge in engineering practices. Therefore, the spallation failure of prefabricated elliptical holes in different orientations under various impact pressures was studied and analyzed by Hopkinson pressure bar. The failure process of long rod red sandstone was recorded in real-time by a high-speed camera during the experiment. The experimental results indicated that spallation did not necessarily occur in all the prefabricated holes, while the impact pressure had a great influence on the spall location of a defective rock mass. Also, the prefabricated holes located closer to the free surface experienced less damage under the impact of lower pressure than the holes located farther away from the surface. In addition, a finite element software, LS-DYNA, was employed to carry out equal-scale modeling and analysis of the circumferential stress variations in elliptical holes. The simulation results showed that the amplitude and wavelength of the stress wave would greatly affect the damage of elliptical defective holes and the initial defects weakened the integrity of the rock. Furthermore, the results showed that the larger the amplitude and wavelength, the lower the stress concentration coefficient of the rock in tensile failure and the most significant damage around the hole was observed at the peak tensile stress.