Longwall face fall refers to the sloughage of coal mass from the coal face wall with little or no warning. The face fall is caused by unstable face conditions or unfavourable roof pressure where large slabs of coal are dislodged and fall from the coal face. It remains a major ground control and safety hazard and has a significant negative fact on productivity and production cost. Falls of large coal blocks from the face can overload the armoured face conveyors and slow down the coal cutting machine. It can also decrease the advance rate of longwall face, increase the maintenance of mining equipment, affect coal production and productivity and risk the safety of workers. Face fall also increases the unsupported area ahead of the longwall shield, which increases the risk of roof cavity in the face-to-tip area and deteriorates the shield-strata interaction. The problem of longwall face fall is becoming increasingly more substantial as the mining height increase.

Theoretical studies are commonly adopted for analysing the failure mechanism of a longwall face. The face fall problem is mostly analysed as a slope stability problem using the limit equilibrium method, including the 2D planar coal slide model, the circular surface slide model, and the three-dimensional (3D) wedge stability model. Sensitive analyses on seam height, roof load, shield capacity, face plate confinement pressure, and mechanical properties of coal have been performed based on these models. Numerical studies of longwall face failure have also been extensively conducted for assessing the extraction height, cover depth, geological disturbance, coal strength properties, and gob load-carrying characteristics on face stability. Efforts to enhance the stability of the longwall face have been performed in the field for decades. Face fall control techniques include the addition of face protection plates in the front edge of roof supports, grouting the coal face wall, increasing the load capacity of shield legs, increasing the face advance rate, reducing the cutting depth of the shearer, decreasing the mining height or face width and mining along the rise in inclined seams. Despite these practices, longwall faces continue to experience face failures and falls.

This Special Issue aims to address the underlying mechanism of face failures and develop engineering solutions to control them. The interactions between the shield and strata will be considered. We welcome both original research papers and review articles that examine recent advanced techniques and engineering approaches for the assessment of face stability and reinforcement of face fall.

Potential topics include but are not limited to the following:

• Numerical modelling of longwall face failure with a consideration of the realistic loading characteristics of the gob materials
• Numerical modelling of longwall face failure with an inclusion of coal cleating system
• The influence of coal cleat orientation relative to face advance direction on face fall
• Development of face grouting materials and grouting techniques for face reinforcement
• Physical modelling of face falls with a consideration of the shield-strata interactions under strong and weak roof conditions
• Optimization of the longwall face design to minimize the abutment pressure ahead of the longwall face
• Monitoring techniques of face displacement and early warning of face fall