Hydraulic fracturing is a widely used technique for exploiting petroleum and natural gas in the formation. In essence, it utilizes a high-pressure pump on the ground to inject the high-viscosity liquid into the drilled well, and hold high pressure at the bottom of the well. When the pressure is greater than the ground stress and the tensile strength of the rock, fractures will initiate from the well wall and propagate vertically along the minimum principal stress. The fluid with proppant is further injected into the well, thus the fractures will extend forward and be filled to prevent closure. As a result, a fracture network with high permeability is formed. This provides a good channel for the flow of water, oil and gas, and the goal of extracting oil and gas can be achieved.

In addition to the petroleum industry, the hydraulic fracturing method has gradually been introduced to other fields in recent years, especially in mining engineering. The application purpose of hydraulic fracturing is mainly divided into two categories: enhancing the permeability of the rock mass and improving the caving ability of the rock mass. For the former, it is similar to the situation of oil and gas exploitation and the hydraulic fracturing is popularly employed to pre-treat low-permeability coal seams to improve gas drainage efficiency. In contrast, the latter is mainly used for the initial caving of the hard roof of the fully-mechanized mining working face and the cutting of the hard roof of the retaining gob-side entry, as well as the pre-splitting of orebody for caving mining in hard rock mines. The above techniques are very effective in preventing dynamic disasters such as rock burst and coal-gas outburst, and improving the mining efficiency of orebody. Also, hydraulic fracturing can be applied to measure in-situ stress, extract geothermal, adjust ground stress and increase hard rock breaking efficiency. It is believed that hydraulic fracturing has widespread application in underground mining.

This Special Issue is dedicated to bringing together high-quality original research and review articles highlighting recent advances and new insights of hydraulic fracturing in underground mining. Submissions showcasing theoretical analyzing, laboratory testing, numerical modeling and field investigations are welcome.

Potential topics include but are not limited to the following:

• Hydraulic fracture initiation, propagation and closure laws under different stress states
• Impacts of anisotropy and heterogeneity of formation rocks on hydraulic fracture propagation.
• Interaction mechanisms of hydraulic and natural fractures.
• Depletion and stress shadow effects.
• Advances in hydraulic fracturing modeling and numerical computation
• Hydraulic fracture monitoring techniques and effect evaluation methods
• Innovative technologies related to hydraulic fracturing in underground mining
• New emerging materials of fracturing fluids, proppants, and chemical additives.
• Environmental challenges in hydraulic fracturing operations.
• Other issues related to fracture mechanics in mining engineering