Study on the weakening of coal wall with section resistance adjustment of fully mechanized support in hard thick coal seam with large mining height

The load acting on coal wall-support in different mining stages varies greatly. The low efficiency cutting of coal wall is the result of the mismatch between the support resistance and mining stage, and the incapability of the mine pressure to effectively break the coal. The support section resistance adjustment technology can meet the requirements of roof safety control in different mining stages (before periodic pressure, normal mining, after periodic pressure), adjust the support working resistance to change the load on the coal wall for fracturing and breaking coal, which can effectively solve the problem of thick and hard coal wall weakening. Based on the engineering background of 1102 fully mechanized working face in Yanghuopan Coal Mine, the technology of support section resistance adjustment in thick hard coal seam matching with mining stage is studied. The simulation results show the following points. ① The peak value and influence range of support pressure at each point of coal wall survey line decrease with the increase of initial support of hydraulic support in normal mining stage and pressure stage of working face. Under the same initial support, the peak value and the influence range of the support pressure on the coal wall in the pressure stage are larger than those in the normal mining stage. ② When the initial support of hydraulic support increases from 2000 kN to 8000 kN, the horizontal displacement of coal wall decreases by 17 mm in the pressure stage and 7.5 mm in the normal mining stage, indicating that reducing the initial support is conducive to weakening the hard coal wall. ③ In different mining stages, the damage degree of plastic zone of surrounding rock decreases with the increase of initial support of hydraulic support, indicating that the damage degree of coal wall decreases. ④ The support resistance is 6000-8000 kN in normal mining stage, 4000-6000 kN after periodic pressure, and more than 8 000 kN before periodic pressure, which can ensure the safety of roof and efficient cutting of thick and hard coal wall. The field application shows the following points. ① In 115 working cycles, the increased resistance state of the hydraulic support accounts for 64.8% of the statistical cycles (75.50% for the first resistance increasing type, 20.16% for the second resistance increasing type and 4.34% for the multiple resistance increasing type). The ratio of the expansion and contraction of the support movable column between 0-3% is 90%, indicating that the hydraulic support has a good capability to operate and control the roof in the field production. ② After adjusting the support resistance of the hydraulic support in sections, the average coal cutting time of the shearer is reduced to 1.8 h under the premise of effective roof control, which is reduced by 21.7% . The coal wall is weakened effectively, and the coal cutting efficiency is improved.