Surrounding rock control mechanism in the gob-side retaining entry in thin coal seams, and its application

Abstract

The stability of the roadside filling body is the key to successful gob-side entry retention in a thin coal seam. However, the existing failure mechanism of the roadside filling body is unclear, and no proactive measures for the high-stress regulation of the roadway-surrounding rock have been proposed. Taking the 2704N working face of Xinyang mine, China, as an example, this study aimed to elucidate the failure mechanism and characterize the mechanical environment of the roadside filling body in order to implement proactive stress adjustment in gob-side entry retention and measures for the structural control of the surrounding rock. The mode of failure of the roadside filling body was analysed, and numerical simulations and field experiments were subsequently performed to characterize the stress environment of the roadside filling body under caving and gob-filling conditions. Finally, regulatory measures for regional stress were proposed. The results showed that adjusting the threedimensional stress fields in the surrounding rock causes the majority of the principal deviatoric stress to concentrate on the filling body, thus causing the surrounding rock to fail. Therefore, decreasing the subsidence space of the roof strata and preventing the accumulation of excessive principal deviatoric stress on the roadside filling body are crucial for regulating the regional field stress in gob-side entry retention and structurally controlling the roadway-surrounding rock. After gob filling, neighbouring units in the 'coal-roadside filling body-immediate roof-filling body in the gob' support system jointly form a skeleton structure that supports the overlying rock through contact force. A powerful force chain network is stored in the skeleton structure. The strong force chains in the gob-filling body bear the majority of the stress imparted by the overlying rock. Relative movement between key blocks is restricted because the key blocks compress each other. Thus, the principal deviatoric stress on the roadside filling body decreases and stability is significantly improved. A new technology that combines a mechanized gob-side entry in a thin coal seam and proactive roof guarding in the gob filling behind the hydraulic supports was designed in accordance with the 'green mining' concept of underground separation of coal from gangue and the requirements for pumped filling materials. The results of this study contribute to the theory and technology of gob-side entry retention and provide a basis for an effective stress adjustment and structural control method in the gob-side entry retention area.