Study On Bolt Support Technology Of Coal Entry Under The Effect Of Double Working-face Mining

Taking the support mode of return air laneway of205working face in Huarun Coal as the research object, its support form and related parameters under the effect of double working-face mining of205and adjacent206were investigated. Firstly, the stability of surrounding rock of return air laneway of205working-face mining was determined through examining the mechanical parameters, composite roof lithology, thickness of every layer and stress environment of no.3coal seam roof; then, anchor supporting scheme was highlighted via the methods of theoretical analysis and engineering analogy; after that, numerical calculation model was established to study the rules of destruction scope of surrounding rock, roof-to-floor convergence, two-sided convergence, stress distribution of coal pillar; based on this, the effect of different support parameters on the stability of the roadway was investigated by changing the anchor rod and anchor rope support parameters to determine the optimized supporting parameters. Results are showed as follows:1. No.3coal roadway surrounding rock was determined to be is III medium stable. The support form and support parameters measured by engineering analogy were as follows:the basic supporting form should be considered as the form when roof is broken, anchor+W steel band (or steel beam)+network, or add the anchor rope; Truss+network, or add the anchor rope; Main support parameter was end anchor, the rod diameter of anchor rod was18-22mm; the bolt interval was0.6～1.0m; the anchor rod length was1.8-2.4m.2. Numerical simulation showed that the failure area of the surrounding rock of return air laneway was basically symmetric before the roadway was affected by mining, but after that the sidewalls of the roadway appeared0.5-m-depth destruction. The anchored scope of roof bolt and the middle of base plate were stress reducing zone, within which the vertical stress was small. The distribution of two-side vertical stress was symmetric, indicating that surrounding rock of205return air laneway was in a stable state before being influenced by mining.3. The stability of the surrounding rock of205return air laneway could be influenced by the mining of adjacent206working face.(1) When the206working face mine to30m in front of the measuring point, compared with20m, little change was observed about the damage to the surrounding rock of return air laneway, by this stage, surrounding rock roadway entered a new steady state.(2) The mining of adjacent206working face would produce greater effects on the surrounding rock when the surrounding rock convergence of206was in the scope between20m in front of the measuring point and40m behind it, after that the surrounding rock of gateway entered into a new steady state along with the continuing mining of206working.(3) Analysis results of coal pillar stress showed that the effect range of206working face mining on the mining of coal pillar was12m, while return air laneway had been less affected, indicating that the surrounding rock of205return air laneway was still in stable state after206working face mining.4. The effect of205working face mining on the stability of return air laneway was showed as follows:(1) From the analysis of yield failure unit distribution of surrounding rock gateway, we could see that10m ahead of working face surrounding rock gateway appeared obvious damage, at this point the roadway was in an unsteady state.(2) The surrounding rock displacement of return air laneway began to increase at30m ahead of working face in advance, while the values increased at a greater rate when at20m, at this stage, the reinforced support in advance should be done to the roof of return air laneway.5. The optimized support scheme is got by several plans comparison using Numerical Simulation, the details of which were as follows:on the roof end bolting four anchors with2.4m length, at each side end bolting three anchors with2.2m length, all the bolt intervals setting as1000x900mm; end bolting anchor cables using "may flower" decorating method, placing single root in the middle, spacing being1600mm, row spacing being900mm.6. Although optimized supporting methods and supporting parameters could satisfy the requirement of205return air laneway, dynamic monitoring was still needed during construction to adjust the supporting parameters based on the results.