Abstract
The stress concentration of gob-side entry surrounding rock is a hot topic in coal mining. In this paper, through theoretical analysis and numerical simulation, the pressure relief mechanism of the gob-side entry retaining by roof cutting and pressure release (RCPR) and the spatiotemporal development law of surrounding rock stress of the gob-side entry were analyzed. The studies showed that the gob-side entry retaining by RCPR shortened the length of the lateral cantilever by directional roof cutting, which weakened the stress level of the gob-side entry. In the meantime, the goaf gangues could play a good filling role by using their breaking and swelling characteristics under the action of gangue-blocking supports and further optimized the stress environment along the roadway. Field industrial tests verified that the gob-side entry retaining by RCPR had a significant effect on pressure relief, and the surrounding rock stress and deformation tended to stabilize after about 160 m of lagging working face. Numerical analysis reproduced the whole process of “mining-retention-using” of roof cutting roadway and revealed that surrounding rocks were always in the zone of relative stress reduction during the whole process. The peak value of mining-induced lateral stress was about 10 m away from the middle point of the gob-side entry. The change of surrounding rock stress could be divided into three stages: significant increase, dynamic adjustment, and stable stage. However, during the second mining, the stress connected zone would appear on the leading working face, and the stress concentration in this zone was significant. Based on the above analysis, we concluded that the new technology could be applied to the medium-thickness coal seam in the composite roof.
Highlights
Gob-side entry retaining (GSER) has significant technical and economic advantages in improving the recovery rate of resources [1], easing the mining and replacement tension, realizing Y-type ventilation [2], and so on
In order to deeply analyze the temporal and spatial development law of the surrounding rock stress field and displacement field in the gob-side entry under the application of the GSER by roof cutting and pressure release (RCPR), it can better guide the field engineering practice. erefore, with the 12201 working face of Ha Lagou Coal Mine as the engineering background, the stress development law of the whole cycle of surrounding rock of gob-side entry was analyzed by numerical analysis method
(3) e numerical simulation results show that the vertical stress acting on the upper roof of gob-side entry is always in the decreasing zone
Summary
Gob-side entry retaining (GSER) has significant technical and economic advantages in improving the recovery rate of resources [1], easing the mining and replacement tension, realizing Y-type ventilation [2], and so on. E caved gangue fills gob with its own breaking and swelling characteristics and quickly forms the supporting structure for the first movement of the rock beam of the basic roof. E stability of gob-side entry will be improved with the protective effect of the “Cut-roof Broken Arm Beam,” the integrated coal beside the roadway, and the filling effect of the gangue. The lower strata are in the state of “given deformation” [25, 27] in the process of breaking, turning, and sinking of the key block of the basic roof; the lateral stress peaks of gob is mainly borne by solid coal, while the bearing structure of roadway mainly bears the direct roof over the roadway that does not collapse, as well as the load of key block B during fracture, rotation, and the gangue. (2) e elastoplastic demarcation point of the basic roof is the fracture location of the key rock B on the
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