Position-optimization on retained entry and backfilling wall in gob-side entry retaining techniques

Abstract

This study investigates the stability problem of gob-side entry retaining (GER) and backfilling wall which located under the key block B. Based on the combined research of elastic-plastic mechanics, structure mechanics and modern theory of mining-induced pressure, the caving characteristic and roof structure over the GER were analyzed, and the vertical force and the torque on retained entry roof were also derived as the position for the retained entry varies. On the basis of the specific geology in Huainan mining area, the results indicate that a relatively more stable position for retained entry neighbors the hinge point of block A and B, and it also located at a scope ranging from this point to the one-third length of block B in horizontal direction. As to appropriate position for backfilling wall, this study recommends partialroad-in backfilling method for GER. Field trial conducted at panel face 12418 of Xieqiao Mine demonstrates that the recommended width for original entry is 3.6 m and the preferred width proportion between original retained entry and original entry is 75 % or so whereas the avoidable one is 88 % or so. These findings provide qualitative references to the mines which share similar geology as what Huainan mining area characterized.

A New Gob-Side Entry Layout Method for Two-Entry Longwall Systems

“…The high dynamic pressure often results in excessive entry deformation and convergence. The cutting cantilever beam theory [32] was proposed to determine the optimal gob-side entry location in GER and the reasonable rib pillar width in GED [9,12,13,16,17,21,23,31,33,34].…”

“…As shown in Figure 1, the fractured main roof (due to the previous panel retreating) is divided into three roof blocks, termed Block A (i.e., the block above the solid coal), Block B (i.e., the cantilever block), and Block C (i.e., the block on the gob) respectively [9]. Block A and Block C are supported by the solid coal and gob materials respectively, while gob-side entry stability highly depends on the subsidence and rotation of Block B. Feng and Zhang [9] carried out theoretical analysis on the optimal location of the gob-side entry relative to Block B.…”

“…Block A and Block C are supported by the solid coal and gob materials respectively, while gob-side entry stability highly depends on the subsidence and rotation of Block B. Feng and Zhang [9] carried out theoretical analysis on the optimal location of the gob-side entry relative to Block B. They concluded that the gob-side entry is much easier to keep stable if it is located close to the hinge point connecting Block A and Block B (i.e., range P 2 in Figure 2b) and the torture of Block B is the dominant force leading to entry instability compared with the resultant vertical force (from both the overburden stress and the weight of Block B).…”

“…Two methods are commonly used to develop gob-side entries at Chinese coal mines, including gob-side entry retaining (GER) and gob-side entry driving (GED). Figure 1a shows the GER entry layout at Xieqiao Mine in China [9]. The headgate of the previous panel is retained after the panel is retreated and will be used as the tailgate of the next panel.…”

“…Figure 1. Two method being commonly used in the gob-side entry layout: (a) gob-side entry retaining (GER), revised by Feng and Zhang [9]; (b) gob-side entry driving (GED), revised by Fan et al [16]. …”