Roof Movement And Mining Pressure Regularity Forfully Mechanized Working Face With Shallow Coal Seam In Liangshuijing Coal Mine

Based on the geological condition of 42111 working face in 421 mining area 4-2 coal seam, the roof movement and mining pressure regularity for fully mechanized working face with shallow coal seam were analysied. By comprehensive using of laboratory test, theoretical analysis, numerical simulation and field measurement, the roof key stratum breaking mechanism of the shallow coal seam was discussesed from the roof rupture structure of shallow coal seam. Both of the roof movement with different basic roof thickness and the influence of mining pressure regularity were revealed. Main results are as follows:(1) It was concluded that the motion law of roof rock in the process of first weighting through theoretical analysis. With the lumpiness of roof rock blocks decrease and the rotation angle θ1 of blocks increase, the favorable conditions of roof rotary instability was increased through the mechanics analysis of asymmetric three hinged arch structure. At the same time, the basic roof prone to sliding instability in the early stages of movement.(2) The roof movement and the stress transfer characteristics with different thickness of basic roof were analyzed by numerical calculation. After working face mining, the vertical stress distribution of basic roof above the goaf presents a distribution of "Inverted V". With the enlargement of the goaf area, the bottom of the "Inverted V" began to appear smooth pressure release area, the basic roof vertical stress presented a shape of "Inverted saddle". When the ratio of basement was less than 0.5, the roof was falling. With the ratio of basement increased, the roof movement characteristics keep basically same with the average coal seam.(3) Through the simulation comparison between the different condition of primary mining and first roof caving. The study drew a conclusion thar whether basic roof can rotary subsiding determined the pressure strength of the first weighting. Compared with not first roof caving, the first weighting process appeared time earlier, and process was a bit long and roof movement form relatively relaxed. At the beginning of mining, the roof was appeared rotating subsidence. The load generated by basic roof breaking movement was the source of the pressure for hydraulic support resistance.(4) According to the analysis of the measured pressure data and summary of field pressure phenomenon, the pressure characteristics of the fully mechanized face in typical shallow coal seam was summarized as follows: the influence range area of lead abutment pressure was small, the hydraulic support resistance has a sharp rise in process of roof pressurization, the periodic weighting length was short, the dynamic load coefficient was large, the ground surface appeared bench convergence, and the basic roof falling by full thick. This is one of typical macro pressure characteristics of shal ow coal seam.