Mechanism of external-misaligned stagger arrangement of roadway driven along next goaf and the 3D combined support technique of adjacent roadway

Based on the 3D (three-dimensional) combined support mechanism of external-misaligned stagger arrangement of roadway driven along next goaf and adjacent roadway in the ultra-thick coal seam, the roadway layout characteristics are theoretically analyzed and found that: ① The roof of coal seam and triangular coal body could keep stable, providing the lateral abutment stress σ_xto solid coal.Therefore, the next goaf side of solid coal has been changed from top to bottom, that is, the lateral abutment stress increases from 0 to σ_x. ② According to the difference in roadway layout and lateral abutment stress, the ultra-thick coal seam from top to bottom is divided into the next goaf side of solid coal zone, the transition zone, and the elastic zone. ③ When arranging a continuous working face roadway driven along next goaf, its surrounding rock is in an elastic state, the roof of roadway carries small load, which locates on the crushing zone and the plastic zone in the next goaf side of the solid coal.The roadway achieves the unity of the stability of the surrounding rock and the low-load.Then the authors propose a 3D combined support technique of adjacent roadway by using high and low roadways of different 3D spatial relationship.Its characteristics of the proposed technique are as follows: ① The active support body has been carried into the deep stable rock stratum in the roadway driven along the roof of the coal seam. ② By strengthening the reinforcement of the next goaf side of solid coal zone, it provides an anchor point for the adjacent roadway along the bottom in the coal seam. ③ The support body in the top of the roadway driven along next goaf has been carried into the deep roof of rock stratum by combining anchorage zone and transition zone, which can achieve a full-length anchorage to fully support function.In order to test the theoretical results, the numerical simulation analysis shows: ① Through the use of external-misaligned stagger arrangement roadway driven along next goaf technique, it achieves the unity of stability of surrounding rock and low-stress, and tests the results of external-misaligned stagger arrangement roadway driven along next goaf's vertical division. ② Under the condition of obviously combined support effect of zero-rock stress field, the top of roadway driven along roof's anchor cables has been carried into the deep basic roof and its roadway's side of anchorage zone. The top of the roadway driven along next goaf's anchor cables has been carried into the deep roof of rock stratum and combined anchorage zone, and stress concentration occurs in these zones.This technique forms an effective anchor point, which is not limited by the thickness of top coal. ③ Through numerical calculation on a field engineering project, it is found that the proposed technique is capable of effectively controlling the large-scale destruction of the surrounding rock roadway than previously used ones.The results can provide a reference for ultra-thick coal seam mining.