Analytical Study on the Stability of Longwall Top Coal Caving Face

Longwall face instability is a critical geotechnical issue in the operation of longwall with considerable mining height and significant caving height. Of the commonly applied research techniques, analytical solutions can provide fundamental insight into key mechanics of face stability to decide if the more in-depth but costly analysis is to be implemented. The paper first presents a mechanical model of face spall in mechanized longwall top coal caving method in which the interaction between coal seam, shield support and roof strata is taken into consideration. An equation for estimation of face spall extent is then developed from the model, using field observations at two typical mechanized longwall top coal caving faces at Quang Ninh coalfield, Vietnam. The estimation demonstrates that the equation is applicable to the cases where the spall is mainly caused by the ruptures of the immediate roof and top coal beams. When the main roof ruptures, the roof pressure is rapidly increased that may cause shield damage and whole face collapse. The paper’s results provide mining engineers with a low-cost tool for quick evaluation of face instability risk in the preliminary stage of mine design.