Coupled Hydro-Mechanical Behaviour of Rock Joints During Normal and Shear Loading

Abstract

The hydraulic conductivity of rock joints is an important parameter controlling fluid flow in various rock engineering applications. The shearing and normal loading have significant effects on hydraulic conductivity of rock joints, the property of which is mainly controlled by hydraulic aperture. Despite the importance of hydro-mechanical behaviour of rock joints, the fundamental micro-scale processes leading to macro-scale observations remain unexplored partly due to difficulties with in situ measurement of hydraulic aperture and its complex relation to roughness and contact area. Therefore, in this study, a series of experiments coupling fluid flow with normal deformability and direct shear are performed on joints with varying controlled roughness at different normal stresses. Along with measuring stress and flow rate, the time-lapse X-ray micro-computed tomography is carried out to explore the evolution of joint aperture and contact area during the experiments. The results of the normal deformability experiments show that the joint conductivity is well correlated to the mean hydraulic aperture of joint profiles. Such correlation, however, is not apparent for the shearing experiment where under high normal stresses, the flow rate decreases continually indicating that damaged asperities hinder the fluid flow. Despite the trend in the average mechanical aperture not following the flow rate in some cases, the trend in the contact area follows the flow rate very closely throughout the shearing process. In addition, the results reveal that despite an increase in contact area with increase in normal stress, it is not physically possible to reach full contact even for the artificially well-mated samples at a high normal stress of 10 MPa. Finally, a new correlation is proposed to relate the hydraulic aperture to joint average mechanical aperture, contact area and roughness. The correlation estimates the experimental flow rates at both normal and shear loading conditions with good accuracy.

Size effect on hydraulic properties of rough-walled fractures upscaled from meter-scale granite fractures

“…As fluid flow in fractured rocks is usually dominated by pre-existing fractures or fracture networks, it is therefore essential to evaluate the hydraulic properties of rock fractures, the accurate characterization of which is of great interest for a wide range of engineering applications. These include the extraction and storage of natural resources (oil, gas, and groundwater) (Gale and Raven 1980;Nelson 2001;Schembre et al 2006;Babadagli et al 2015;Ishibashi et al 2020;Guo et al 2022;Wang et al 2022), enhanced geothermal production (Gringarten et al 1975;Bächler and Kohl 2005;Huenges 2010;Grant 2013;Zhao 2016;Sawayama et al 2021), the geological disposal of nuclear waste (Cvetkovic et al 1999;Bodin et al 2003;Neuman 2005;Tsang et al 2015;Thatcher et al 2021), and the geological sequestration of carbon dioxide (Saidi 1987;Nelson 2001;Ringrose et al 2013;March et al 2018; Lee and Babadagli 2021;Pirzada et al 2022). However, the capacity to accurately estimate the hydraulic properties of fractures is hindered by complex influencing factors such as stress conditions (Gale and Raven 1980;Raven and Gale 1985;Yeo et al 1998;Olsson and Barton 2001;Baghbanan and Jing 2008;Rutqvist 2014;, geometric properties (e.g., roughness, aperture dimensions), and fracture stiffness (Zimmerman and Bodvarsson 1996;Konzuk and Kueper 2004;Li et al 2020;He et al 2021).…”