Mechanism of shaft deflection caused by asymmetric mining in thin bedrock and deep loose strata

Aiming at the mechanism of shaft deflection in asymmetric mining of thick loose layer and thin bedrock,the shaft deflection of Shandong Guotun coal mine was investigated.Based on the mechanism of overburden movement and deformation in mining of thick loose layer and thin bedrock,coal mining subsidence theory,soil consolidation theory,random medium theory,and the superposition principle,the calculation formula of overburden movement and deformation under the joint action of coal seam mining and bottom water drainage in this kind of stratum is given.The results are verified by field measurement.Based on the analysis of the movement and deformation characteristics of overburden in the mining of this kind of stratum,the mechanism and influencing factors of shaft deflection under the combined action of asymmetric mining of thick loose layer and thin bedrock and bottom water drainage are revealed. The research shows that under the combined action of coal seam mining and bottom aquifer hydrophobic consolidation,the coefficient of stratum subsidence and horizontal movement,the range of subsidence and horizontal movement are greatly increased.By inversing the deflection parameters of Guotun mine shaft,it is obtained that the tangent of the main influence angle of the loose layer is 0.6,which is far less than 2.41-3.54 specified in the code for coal pillar setting and coal pressure mining under buildings,water bodies,railways and main roadways.The mechanism leading to the shaft deflection is that the superposition of bottom aquifer hydrophobic consolidation settlement caused by coal seam mining causes the main,auxiliary and air shafts of the mine to be within the influence range of overburden movement and deformation. Under the condition of asymmetric coal seam mining (northwest direction),the overlying deep loose layer moves horizontally in this direction,resulting in shaft deflection.The shaft deflection is positively correlated with the bottom aquifer thickness M,the thickness ratio k0 of loose layer to bedrock layer,and the drawdown Sw of bottom aquifer,and the influence sensitivity is Sw,k0,M in turn.