The study of Thermal-Hydraulic-Mechanical (THM) coupling behaviour is significant in many aspects of geological engineering, such as oil and gas extraction, geothermal energy, nuclear waste disposal, and mine engineering, where the geological media usually consists of fractured rock. Insights into THM coupling behaviour are generally based on both experiments and numerical modelling, from micro- to macro- scale. Laboratory tests have confirmed that coupling between rock stress, fluid flow, and temperature, although affected by various petrophysical quantities, has been shown to be strongly dependent on the geometry of fracture networks, fluid characteristics, and stress and temperature conditions. Numerical simulation has become an efficient tool widely appreciated by geotechnical researchers. With the development of numerical methods, such as discrete element method (DEM), finite element method (FEM), meshless method, and high performance computing technologies, more complicated virtual models that are closer to the real world can be efficiently established and processed, generating more reliable results for geotechnical design and assessment.

In recent years, many methods including laboratory experiments, theoretical analysis, and numerical simulation have been employed to investigate fluid flow in fractured rock masses under various stress and temperature conditions. However, comprehensive insight into coupled THM processes is often hampered due to the fact that rocks and rock formations are enormously complex. Therefore, further studies on THM coupling behaviour of fractured rock masses are still needed, such as mechanical and permeability characteristics of fractured rock masses, nonlinear flow in fractures, and new experimental and numerical methods.

The aim of this Special Issue is to bring together papers on different topics related to THM coupling behaviour of fractured rock masses, such as experimental founding, constitutive models, and their engineering applications. Submissions relating to theory, experiments, techniques, numerical methods, and engineering projects are all welcomed, including both original research and review articles.

Potential topics include but are not limited to the following:

• Nonlinear flow behaviour in rock fractures under THM coupling
• Analysis and modelling on hydraulic fracture initiation and propagation
• Mechanical and permeability characteristics of rock
• Constitutive modelling and numerical methods
• Case studies related to THM coupling
• Microscopic seepage theoretical developments
• Gas-liquid two-phase fluid in rock fractures under THM coupling
• Mud-water inrush disaster in geotechnical engineering