The evolution of the long-term mechanical, hydraulic, and transport characteristics of rock fractures must be predicted in advance by considering the issue of the underground deposits of the energy by products of high-level radioactive waste. This paper presents slide-hold-slide direct shear experiments conducted for rock salt (halite) specimens with single fractures so as to investigate the effects of load holding on the mechanical properties of rock joints. From the experimental results, it is confirmed that the shear stress reduction can be observed during load holding. It is also confirmed that the shear strength recovery can be observed after load holding and it is found to increase with the increment of load holding period. This is because the dominant factor in the shear strength recovery during holding may be attributed to a purely mechanical process, like creep deformation at the contacting asperities.
In this study, a series of permeability experiments on both intact rock and a single fracture in sandstone and on a single fracture in siliceous mudstone has been conducted under confining pressures of 3 – 15 MPa, and at temperatures of 20 – 90°C for several hundred days in each experiment. Spontaneous alteration of permeability and dissolved mass fluxes have been observed. In sandstone, the permeability of intact rocks little changed until a couple of hundred days, then it started to increase with time. In mudstone, the permeability in a single fracture monotonically decreased with time and reached a quasi-steady state within one month. However, it started to increase with time after ~100 days. This augmentation in the permeability in sandstone and mudstone should be attributed to mineral dissolution within the void spaces. In contrast with the sandstone results, the fracture permeability in mudstone resumed decreasing with time throughout the rest of the experiment. A coupled chemo-mechano conceptual model, accounting for pressure and free-face dissolutions, is utilizedto follow the evolution of the permeability observed in the experiments. The model predictions show a relatively fair agreement with the experimental measurements, although further considerations and modifications are found to be required.