Dynamic tensile behaviour under impact loading for rocks damaged by static precompression

In geotechnical engineering projects, rock masses are subjected to various degrees of disturbance from geotectonic movements, rock drilling and mining before they are subjected to dynamic loads such as rock bursts, earthquakes, and blasting. We aim to investigate the dynamic mechanical properties, strain field, energy evolution, and progressive cracking of damaged sandstone under impact loading. In this study, sandstone specimens undergo various damage degrees caused by precompression and are characterized by computed tomography (CT) imaging. Then, the damaged specimens are subjected to impact tensile loads by employing a split Hopkinson pressure bar (SHPB) coupled with a high-speed camera and digital image correlation (DIC). The experimental results show that the energy dissipation density ratio, scale of the initial central crack, strain, and level of rock fragmentation in the vicinity of the bar-sample interfaces all increase with increasing driving pressure or sandstone damage degree. In contrast, the regular pattern of dynamic tensile strength is the opposite. We also find that the total strength rises before the prestress ratio of 0.2 and subsequently decreases as the sandstone's damage degree increases. The rock's dynamic tensile strength reduction ratio grows with the Weibull distribution as the damage degree expands. In addition, the function of the growth rate of the dissipated energy density ratio concerning the sandstone's damage factor follows the Weibull distribution. These findings are of great significance to studying the mechanical responses of damaged rock and risk mitigation under dynamic catastrophes such as rock bursts, earthquakes, and blasting in rock engineering projects.