Numerical analysis of the stability of a gob-side entry retaining in non-pillar coal mining using discrete fracture network modelling

An innovative approach to the gob-side entry retaining non-pillar mining is being used to increase the coal seam recycling rate and productivity in China’s coal mining. The retained entry with a sidewall formed by gob caved-in filling rocks is unique in this method and the stability of caved-in material is critical to ensure efficient and safe mining activities. In this paper a numerical investigation on the stability of the gob-side entry is conducted using a discrete fracture network (DFN) model developed by the Massachusetts Institute of Technology (MIT), GEOFRAC, in combination with discrete element modelling (UDEC). The proposed method is applied to a case study of a gob-side retained entry in an underground coal mine in China. Fracture traces are measured along the gob-side wall of the entry, and statistical methods are used to estimate the fracture intensity and the mean fracture areas, which are the key inputs to GEOFRAC. Fracture networks generated by GEOFRAC estimate the rock blocks in the filling body, and simulations with UDEC are done to evaluate the stability of the gob-side entry. Two models are developed, one considering the generated fractures and the other considering no fractures within the gob-side filling. The results show the effects of considering the fractures in the filling body on the distribution of displacement and field stress in the gob-side entry zone. Also, the stability under the mining impact loading, due to periodic roof caving, is simulated, providing the basis for the optimization of the design of the entry support.