Load–unload response ratio characteristics of rock materials and their application in prediction of rockburst proneness

The load–unload response ratio (LURR) theory was introduced to study the rockburst proneness of rock materials, and a rockburst proneness criterion was proposed in this project. First, ten rocks (including three types of granite, three types of sandstone, one kind of limestone, and three types of marble) were chosen on which to carry out the uniaxial step load–unload test, and then a calculation method for LURR at different load–unload points based on a data-fitting algorithm was presented. The LURR-strain curves of the ten rocks were divided into the decrease stage, the steady stage, and the increase stage, and the starting point of the increase stage was defined as the LURR S-R (start rise) point. Subsequently, the LURR difference method was put forward to determine the LURR S-R point scientifically. Finally, the relationship between the lag time ratio (the lag time ratio was defined as the ratio of the time from the LURR S-R point to the peak strength point to the time of the whole loading period) and the degree of rockburst proneness for ten rocks was investigated; the results show that there is an obvious correspondence between the lag time ratio and the degree of rockburst proneness. Then, a rockburst proneness criterion based on the lag time ratio index was proposed. In addition, the real-time pre-warning of rockburst proneness based on the dynamic lag time ratio index was also presented and analysed.