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

摘要

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 30° and 60° square openings are more susceptible to damage than those having a 0° 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.