Mesodamage Characteristics of Rock with a Pre-cut Opening Under Combined Static-Dynamic Loads: A Nuclear Magnetic Resonance (NMR) Investigation

To investigate the mesodamage evolution of rock specimens containing a pre-existing opening under integrated static and dynamic loading, the nuclear magnetic resonance technique was utilised in this study. The changes in the transverse surface relaxation time (T (2)) distribution, peak area, and porosity of the specimens prior to and due to varying pre-stresses under an identical dynamic loading were systematically analysed. The experimental results show that as the pre-stress level increased the size and the amount of the pores, the peak area and the porosity increase, indicating that more damage is induced under a high pre-stress. Under identical loading conditions, the specimens having 30A degrees and 60A degrees square openings are more susceptible to damage than those having a 0A degrees square opening. However, compared with the specimens containing a circular opening, the specimens with a square opening are more seriously damaged. The hoop stress concentration surrounding the opening induced by the pre-stress and subsequent dynamic loading was further demonstrated. The result indicates that the initiation of rock fracture occurs in the maximum hoop stress concentration area.