At present, the engineering challenges of deep rock or soil have attracted wide attention. The stability and safety problems of deep rock or soil are encountered in the fields of coal, oil, national defence and nuclear waste storage. The primary task to be solved in deep rock engineering is how to ensure production safety in complex deep geological conditions. Under the conditions of high stress, temperature and water pressure (or gas pressure), a large number of disastrous accidents such as water flooding, water inrush, roadway collapse, gas outburst and gas explosion have taken place, causing a great threat to the health and safety of field workers. It is very important to correctly understand the mechanism of these disasters, which are reflected by the behaviour of geotechnical materials and fluids in the process of deep excavation.

The migration of water and gas in geotechnical materials during underground excavation is a complex problem, involving multi-phase (solid, liquid and gas), multi-scale (nano to macro) and multi-field coupling (mechanical, thermal, chemical, water, gas, etc.). For example, high temperature can change the mechanical properties of rock due to thermal stress. Creep is also sensitive to high temperature and high osmotic pressure. In addition, during the exploitation of deep resources (coalbed methane, shale gas and geothermal), fractures are usually artificially induced in the reservoir in order to enhance production efficiency. Rock damage or crack propagation in the reservoir may complicate the problem. Due to complex affecting factors in the environment of high ground stress, high temperature and high seepage pressure, the mechanism of water or gas flow and deformation of geotechnical materials induced by excavation disturbance are not fully clear. Further research is needed in order to take appropriate measures to prevent hazards induced by water or gas flow.

The aim of this Special Issue is to collate original research with a focus on some of the current challenges faced by academic and industrial researchers in this field. We welcome original research and review papers on all relevant topics, especially theoretical development, analytical methods, numerical methods, geotechnical tests, field investigations and case studies.

Potential topics include but are not limited to the following:

• Long term stability analysis of deep surrounding rock
• Mechanism of multi-field and multi-phase flow under deep disturbance
• Stability and seepage field analysis of surrounding rock of underground oil storage
• Roadway support method in deep multi-field coupling environment
• Stability analysis of surrounding rock of deep tunnel in water-rich area
• Mechanism of gas dynamic disaster in coal mining
• Water inrush mechanism of deep and long tunnel
• Fracture mechanism of surrounding rock in deep excavation
• Gas migration mechanism and gas drainage technology
• Exploitation of geothermal resources