Beishan granite is a potential host rock for a high-level radioactive waste (HLW) repository in China. Understanding the hydromechanical (HM) behavior and permeability evolution of Beishan granite is important for the HLW repository safety. Therefore, the granite of Beishan in Gansu province was studied. HM coupled tests are carried out on Beishan granite under different pore pressures. The results show that the initial pressure difference has little influence on permeability measurement before dilatancy starts. However, after onset of dilatancy, the permeability increases with the increasing initial pressure difference. The initial permeability of Beishan granite is about 10−18m2 under a confining pressure of 20 MPa. In the initial loading phase, the permeability shows a relatively large reduction. Then, the permeability almost keeps constant until dilatancy starts. From dilatancy point to peak stress, permeability increases linearly with volumetric strain. The proposed permeability evolution rule is implemented into a numerical code to perform HM coupled simulations. The simulation results show that the damaged zone first appears at the model boundary and then extends to the inside, forming high volumetric strain areas. And it provides seepage channels for fluid flow. The macroscopic fracture patterns indicate that pore pressure accelerates rock degradation during HM coupling. The obtained results help to understand the damage mechanisms of granite caused by pore pressures and are of great importance for the safety of a HLW repository.

The concentration of abutment pressure acting on coal seams induced by mining is a key factor to trigger rock burst. Understanding of abutment pressure or stress concentration is fundamental in preventing and controlling rock burst. The influence on abutment pressure fluctuation caused by the inhomogeneity of coal seams needs to be considered, but it is difficult to obtain by the present usual ways such as acoustic transmission, electromagnetic wave transmission, etc. In this article, the relationship between the amount of cuttings drilled in a coal seam and stress level was analyzed by considering the effect of drilling cutting expansion, and the drilling cutting test was carried out in Xinglongzhuang Coal Mine, Shandong Energy Ltd. It is found that the amount of cuttings drilled is positively related to the degree of stress concentration in both the plastic fracture zone and elastic zone. The amount of drilling cuttings is closely related to the roof weighting. In addition, the irregular fluctuation of drilling cuttings is an approximate map of distribution of stress concentration because of the non-uniformity of cracks and other defects in the coal seam. In order to meet the need of rock burst prevention by accurate pressure relief in high-stress zones, enough boreholes are needed.

An insight into the damage characteristics of host rock is important for permanent disposal of high-level radioactive waste (HLW). Single loading and multiple loading tests for Beishan granite were carried out. The acoustic emission (AE) monitoring system was utilized simultaneously to measure the damage evolution in the specimens. The results show that, during single loading the AE signal has been maintained at a very high level after dilatancy. But a decreasing trend of AE signals can be observed when the axial stress approaches the peak stress. While during multiple loading, AE signals are mainly generated in the loading period in the elastic stage. However, in the failure and residual stages, AE signals generated in the unloading period are considerable. Most of the AE waveforms have a dominant frequency of less than 200 kHz and amplitude of less than 80 dB, and three frequency bands are obtained. In addition, the amplitude increases with the increase of loading stress. Furthermore, the obtained AE b-values indicate that the relative proportion of micro- to macro-cracks increases first and then decreases with increasing confining pressure. And the AE a-values and b-values confirms that micro cracks develop rapidly in the damage stage and lead to the formation of macro cracks in the residual stage for the specimens experienced multiple loading.