Study On Overlying Strata Structure Development And Roof Control Of Longwall Face Under Thin Topsoil And Thin Bedrock In Shallow Seam

Focus on the determination of working resistance of hydraulic supports of longwall face under thin topsoil?the thickness of topsoil is less than the height of unloading arch?and thin bedrock in shallow seam,taking No.30102 working face of Niushan Coal Mine as the research object,using theoretical analysis,3DEC numerical simulation,multiple regression analysis,formula adjustment analysis and on-site monitoring and other means,the development of overlying strata structure and determination method of working resistance of hydraulic support were researched,the results show that:?1?Under the conditions of longwall face under thin topsoil and thin bedrock in shallow seam,it is easier to support the roof before main roof first weighting.The most dangerous stage is main roof first weighting stage.Even if the support strength is increased,it is difficult to avoid the roof bench convergence in roof control area,but the roof bench convergence can be reduced when the stable support-surrounding rock structure formed.?2?Under the conditions of this study,the main roof ruptures and the bench convergence will cause the unloading effect of the topsoil.The mechanism is as follows:?1?before the main roof ruptures,the load of topsoil approximates the gravity caused by the full thickness of the topsoil.?2?when the main roof ruptures,due to the characteristics of stope under thin bedrock in shallow seam,the main roof rock blocks are difficult to be self-stabilized and the bench convergence occurs.The upper topsoil move to the space caused by the bench convergence.Under the effect of the press and friction between soil particles,the load is transferred to the both sides,which leads to the decrease of topsoil load on the main roof rock blocks,and the structure becomes more stable.?3?As the bench convergence of the main roof rock blocks increases,the degree of the press and friction between soil particles also gradually increases,and the topsoil load decreases continuously.?4?When the topsoil load decreases to match the support strength of the hydraulic support,the stable support-surrounding rock structure is formed.?3?Define the unloading coefficient?=topsoil load before main roof rock blocks bench convergence/topsoil load before main roof ruptures,and the unloading coefficient when main roof first weighting is only affected by allowable bench convergence?S and topsoil internal friction angle?.The formula is as follows:?=1-0.258ln??S+1????.?4?Under the conditions of this study,the required working pressure of hydraulic support should be calculated according to the main roof first weighting stage,and the 13 factors influencing the required working resistance of unit width of hydraulic support are ranked as follows:main roof thickness h>allowable bench convergence?S>topsoil internal friction angle?>main roof rock block friction angle?>topsoil thickness H?topsoil bulk density?₄similar?>roof control area width l_k>top coal thickness h₂?Top coal bulk density?₂ similar?>immediate roof thickness h₁?immediate roof bulk density?₁similar?>main roof bulk density?₃>main roof tensile strength R_T.?5?The required working resistance of the hydraulic support in No.30102working face of Niushan Coal Mine is 4 863 kN.The hydraulic support,reached the required working resistance by replacing the column,is feasible in the mining process.The bench convergence reached 23³5 cm during the main roof first weighting stage?the bench convergence at the center of working face is largest?.