Research On The Influence Factors And Mechanism Of Top-coal Break On Fully-mechanized Caving Face In Steeply Dipping Soft Seam

The mechanism of top coal break on fully-mechanized caving face in steeply dipping soft same is extremely complex and has many influence factors. During the mining process, the breaking and falling of top-coal has a crucial effect on support stability. Research on the influence factors and mechanism of top coal failure on fully-mechanized caving face in steeply dipping soft same has great significance to control “support- surrounding rock” system stability and ensure the safe highly effective production.By the integrated methods of physical simulation, numerical simulation, theory analysis and engineering practice, the influence factors and mechanism of action to top coal failure are studied. The studied indicate that:Different dip angle, seam strength, mining-caving ratio and repeatedly supporting are major factors of top-coal breaking. Along with dip angle increase the stress distribution on top-coal present asymmetric characteristics; along with seam strength decline the tip-to-face top coal generates larger deformation and range; along with the race of mining-caving ratio the deformation degree of tip-to-face top coal will be aggravated; repeatedly supporting will lead to the residual strength of top-coal located in the roof control area, and further broken into granular medium which has lost macroscopic mechanical connection. Along the four factors dip angle and seam strength are internal cause, mining-caving ratio and repeatedly supporting are external cause.The “load applied object” of top-coal is composed of main roof “structure” and the lower granular-mass load stratum. Along the strike the main roof “structure” will experience the conversion process as “cantilever beam” �' “masonry beam” �'“lower position micro structure”. During the working face advancing, the press on top-coal is mainly provided by the instability of “lower small structure” and load stratum. Affected by the dip angle, the removed of “key layer” along the tendency will lead to the “structure” location and instability form expressed different characteristic, further makes the extent of top-coal breaking inconformity. When top-coal located up over the support, with the decreased of confining pressures the residual strength of top-coal declined dramatically. For the time being, the repeatedly supporting by support will case the damaged top-coal under the abutment pressure broken again, especially in soft seam, the extent of top-coal breaking will be more violent and the impact area will be closer to the coal wall, and will easily cause the top-coal falling. Meanwhile, excessive mining-caving ratio would weaken the capability of thin top-coal load resistance, thus make the top-coal broke into granular medium prematurely. The above factors’ coupling and superposing will extremely weakened the stability of “support-surrounding rock” system.The characteristics of working resistance distribution and support stability of 1121 working face have sufficiently validated the damage effect on top-coal of all the influence factors. Based on these, the “key control measures of supporting system stability on fully-mechanized caving face in steeply dipping soft seam” has been proposed.