Coupled THMC simulator that can describe the long-term evolution in rock permeability and stiffness due to mineral reactions within rock fractures generated by cavity excavation. The developed simulator was applied to perform the long-term prediction by assuming the subsurface environments near the radioactive waste repository. Analysis results show that although generated fractures during excavation of disposal cavity result in the permeability increase and the elastic modulus decrease, after the excavation, the permeability and the elastic modulus of the damaged zone decreased to that of the intact zone and increased to 30 % of the initial state, respectively. These changes of rock permeability and stiffness after excavation were driven by pressure dissolution within rock fractures. Overall, analysis results indicate that pressure dissolution within the fractures has significant influence on the evolution of hydro-mechanical damage of rock generated by cavity excavation. 1. Introduction It is important to predict the evolution of the hydraulic and mechanical properties of rocks surrounding the disposal facility for evaluating the performance of geological disposal system of high level radioactive wastes (HLW). The change of material properties of surrounding rocks should be caused by influence of multi-physics phenomena including the heat transfer from waste package, the transport of groundwater, fracture generation during cavity excavation, and chemical reactions between rock minerals and pore water. Thus, coupled Thermal-Hydraulic-Mechanical-Chemical (THMC) numerical simulation considering above-mentioned multi-physics phenomena should be required. Among the processes of HLW geological disposal, fracture generation during cavity excavation exerts significant influence on the change of hydraulic and mechanical properties of surrounding rocks (Aoyagi et al., 2019). In addition, after cavity excavation, mineral reactions such as pressure dissolution within generated fractures may control the long-term evolution of rock permeability and stiffness (Yasuhara et al., 2011). However, existing coupled THMC simulators cannot evaluate the above long-term evolution of rock permeability and stiffness due to mineral reactions.

Because the topography of the fracture surface evolved in a long-term under different conditions, it exerts a significant influence on the flow behavior. The flow would bypass the contact area between the fracture surfaces under the coupled conditions. In order to study the different characteristic factors which control the flow behavior, this work has studied the hydraulic properties of a single rock fracture by utilizing a granite specimen. The granite specimen was fixed within the triaxial vessel under the confining pressure. Several permeability tests were performed at three different temperatures (20, 60 and 90 °C). The permeability value was evaluated at different times in both short-term and long-term tests. Results show that the permeability values changed regularly in the short-term tests under different confining pressure conditions. In contrast, irregular phenomena of the permeability changing was found in the long-term tests under the constant confining pressure of 3.0 MPa. Especially at 60 °C, the permeability decreased in the early experimental period, but it increased after 60 days and varied with slight oscillation. Moreover, the permeability decrease under a higher temperature can be confirmed in both short- and long-term tests. The reason for the permeability reduction may be considered as the chemical effects under coupled processes. In this study, the effluent from the fractured specimen was also sampled in the long-term tests to evaluate the mineral dissolution. The phenomena that the topography of the fracture surface evolved with time might be controlled by the evolution of the mineral dissolution, which resulted in the permeability variation and changed the contact area between the fracture surfaces. The geometrical alteration in fractures that should have affected the permeability evolution is needed to be further examined. 1. Introduction It is well known that the mechanical and hydromechanical properties of fractures within rock mass would change under various conditions. The coupled THMC (thermal-hydraulic-mechanical-chemical) processes exert significant influence on the subsurface fluid flow in geological systems (Polak et al., 2004; Min et al., 2009). Several previous experimental works have been investigated on the hydraulic properties of rock fracture under coupled hydro-thermal conditions (Polak et al., 2003; Yasuhara et al., 2006). In these researches, the phenomena that chemical and mechanical compaction can reduce the permeability of the fracture was especially focused. The reduction of the permeability may be explained by the mechanism of pressure solution (Polak et al., 2003; Yasuhara et al., 2006). Yasuhara et al. (2004) performed the permeability tests which proved that the chemical interaction on the fracture asperities and the structure of a fracture might be changed by the pressure solution (Yasuhara et al., 2004; 2006). However, the permeability may not reduce monotonously under higher temperature conditions in the long term even though some researchers claimed that the permeability may decrease at a relative high temperature (Yasuhara et al., 2006; Kohl et al., 1995; Morrow et al., 2001; Barnabe, 1986). The complexed processes may alter the fracture surface roughness and further change the permeability of the fractured rock mass. Nevertheless the fracture surface roughness and the fracture aperture change can hardly be obtained directly. Moreover, there is lack of experimental data about the morphology of fractures at various confining stress (Bing et al., 2004). The relationship between the aperture change and the contact area is also difficult to be measured. Therefore, this work studied the short- and long-term permeability variation at different temperatures. The changing of hydraulic aperture under constant stress and temperature conditions was also investigated.

The joint surface roughness is one of the important parameters which influences the mechanical and hydro-mechanical behavior of rock joints. In most cases, the joint roughness coefficient (JRC) was used to quantitatively express the roughness degree. In this study, we applied the mean Z 2 values of all profiles on the joint surface, rather than picking out one or several typical profiles, as estimated parameter to predict the JRC values. The calculated Z 2 values and JRC values diminish with the increase of sampling intervals. Through analyzing the measured JRC values under three sampling intervals, the 1.0 mm interval is pointed out the most appropriate one to evaluate the joint roughness. In addition, we evaluated and compared the JRC values of joints within granite specimens that have different mechanical properties and weathering state by two different methods (Z 2 method and backward analytical method). From obtained results, The Z 2 method could relatively accurately predict the JRC values of unweathered material at 1.0 sampling interval, while overestimate the JRC values in weathering state. It may be attributed to that the weather process may weaken the mechanical properties of JCS values and basic friction angle which are the controlling mechanical factors of definitional JRC values. Moreover, the Z 2 roughness metric does not take into consideration the mechanical proprieties and topography characteristics of weathering rock mass. In total, Z 2 method should be improved by considering additional parameters related to mechanical properties of rock joint (i.e. distribution of contact area within joint surface). 1. Introduction It has long been recognized that the rock joint is one of the crucial components of a rock mass. The rock joint surface plays a significant role in controlling the mechanical and hydro-mechanical behavior. In previous study, a parameter of joint roughness coefficient (JRC) is proposed to quantitatively express the roughness degree (Barton and Choubey, 1973). Nevertheless, measuring definitional JRC values still needs a tilt test or direct shear test to make a reliable estimation. To overcome this limitation of experiments, ten typical profiling lines are defined and visual comparisons are made to estimate roughness degree (Barton, 1977). However, this method is strongly dependent on the subjectivity and experience level of the researcher. To remove this bias, the root mean square first derivative values (Z 2 ), a statistical numerical parameter, is revealed, which is also easily to be determined.