Study On Deformation And Movement Law Of Thin Bedrock In Thick Coal Seam Mining In Zhaogu No. 1 Coal Mine

In recent years,coal seam mining under thin bedrock with overlying thick loose layer in China’s central coal mines has resulted in multiply supports crushing and roof water-sand inrush accidents in the fully mechanized coal mining face,which has seriously affected the safety production of the working face.Based on the mining conditions of fully-mechanized coal face 12051 in Zhaogu No.1 coal mine,with methods of numerical simulation,theoretical analysis and field observation,the thesis studied deformation and movement law of coal face overlying thin bedrock,and the main reasons of supports crushing when roof is weighting.There is covered with Quaternary thick loose layer with an average thickness of 480.0m in Zhaogu No.1 mine.Loose layer is composed of clay and sandy clay with multi-layered gravel aquifer.The main coal seam Ⅱ 1 is near horizontal extremely thick coal seam,but bedrock overlying coal seam is thin and has an average thickness of 44.8m.According to coal face roof and floor classification for gently inclined coal seam in China,controllable degree of coal face in Zhaogu No.1 mine surrounding rock belongs to difficult control one,and the working face should use chock-shield support.Through numerical simulation,the deformation movement of overlying thin bedrock and the distribution law of abutment pressure in front of coal face during top-slice mining and one-pass mining of Ⅱ1 coal seam and the development law of "two zones" after thick seam mining were studied.The results showed that,with the increase of mining height,the development height of "two zones" has increased,while the ratio of caved zone height to mining height and the ratio of the fractured zone height to mining height has decreased.Mining height has less influence on the roof weighting interval.The abutment pressure in front of coal face tends to be stable after main roof first weighting,which manifests in the maximum stress concentration coefficient and the plastic zone range are basically remained unchanged.Through strata control observation,the strata pressure behavior law of top-slice mining coal face under thin bedrock was systematically analyzed,relevant parameters such as the first weighting interval of main roof 45.4m and periodic weighting interval of main roof 13.6m and the dynamic load coefficient in periodic weighting 1.65 were obtained.Through the theoretical of “key stratum”,the compound key stratum in thin bedrock overlying fully-mechanized coal face 12051 was studied.The results showed that,the compound key stratum broken under the effect of loose layer load.The compound key stratum breakage lead to overall fracture of the bedrock,leading to direct flow of water-flow fractured zone to gravel aquifer at the bottom of thick loose layer,which will cause supports crushing and roof water-sand inrush in coal face.The conclusions provide experience and reference for safety and efficient coal mining under thin bedrock with overburden thick loose layer.