Influence of water on rockburst proneness of sandstone: Insights from relative and absolute energy storage

Abstract

To fully understand the influence of water on rockburst proneness from energy storage viewpoint of rock and to check the performance of energy-related rockburst proneness indexes, several groups of uniaxial compression tests at different stress levels are performed on three types of red sandstone specimens (i.e., the saturated, natural, and oven-dried specimens). The method of combining strain energy calculations and experimental observations is used to assess the rockburst proneness. The progressive failure of the three types of specimens is recorded by a high-speed (H-S) camera, and the rockburst proneness is comprehensively assessed by considering the failure features of the rock specimens (including the fracture sound, fragment ejection, fragment distribution, and far-field ejection mass ratio). The laboratory results reveal that the rockburst proneness of the natural and oven-dried sandstone specimens is similar. However, compared with the natural and oven-dried specimens, the water-saturated specimens exhibit a visible weaker rockburst proneness. It is also evident that the linear energy storage and dissipation laws are applicable to the saturated, natural, and oven-dried specimens. Most interestingly, the energy storage and energy dissipation coefficients are nearly immune to the presence of water in the red sandstone. Based on this, the definitions of absolute energy storage capacity and relative energy storage capacity are adopted to describe the influence of water on the energy storage performance of rocks. It is found that water dramatically weakens the absolute energy storage capacity, but has little and negligible effect on the relative energy storage capacity of sandstone. Considering the direct and indirect indexes, the accuracy of several representative energy-related rockburst proneness indexes is comprehensively compared in terms of the far-field ejection mass ratio, and their performance is discussed from the relative and absolute energy storage aspects. According to their performance, it is strongly recommended to use the direct index for determination of rockburst proneness when energy-related indexes are used.