| Shaft of coal mines play a critical role as "throat" in transportation between surface and underground working site in mining operations,and it is crucial in safety production of mines.Since 1987,more than 200 shafts in China’s Huang-Huai and Northeast area have been damaged one after another.After extensive research for more than 30 years,it has basically revealed the mechanism of vertical deformation and near circumferential fracture of shafts in China’s Huang-Huai and Northeast area,and has been recognized.The corresponding shaft damage repair and control technology has also been mature.In recently years,a new damage form of shaft which is co-existing of shaft deflection and vertical compress deformation in alluvium portion of thick topsoil(over 400 m)and thin bedrock strata were found in Juye coalfield,Shandong,China,the failure mechanism is unclear,and the relevant research at home and abroad is still blank.In this paper,the deflection of the shaft in thick topsoil and thin bedrock is taken as the research object,the hydrogeology,engineering seepage mechanics,mining engineering,underground structure mechanics and other relative theories are applied,and the research methods of test,theoretical analysis and in-situ monitoring are used to study stratigraphic subsidence law and cause of shaft deflection in thick topsoil and thin bedrock.The research results will show its important theoretical significance and application value on optimizing protective coal pillar design of surface plant within thick topsoil(over 400 m)and thin bedrock strata,as well as safety operation of shafts under similar geological conditions.The ETAS and NMR test systems were used to study the permeability and hydrophobic consolidation mechanical properties of the aquifer at the bottom of thick topsoil under high stress.The pore structure evolution mechanism of the bottom aquifer under high stress was obtained,and the relationship between the permeability coefficient,pore pressure dissipation rate and the pore structure of the bottom aquifer was established,and the permeability and pore pressure dissipation laws of the bottom aquifer under different confining pressures and hydraulic gradients are revealed.The research results show that the aquifer at the bottom of the thick topsoil in the Guotun Coal Mine is a typical clayey sand,with the main mineral composition of quartz and montmorillonite,and its compression index Cc ranges from 0.03 to 0.05.Under the condition of isotropic pressure,the permeability coefficient of low confined water and high confined water decreases with the increase of confining pressure,and the permeability coefficient at a confining pressure of 1 MPa is significantly larger than that under high confining pressure.When the confining pressure of the sample is greater than 4 MPa,the permeability coefficient of low confined water and high confined water are less than 1×10-8 cm/s.In the process of isotropic hydrophobic consolidation,the strain is mainly radial strain,and the compression deformation of sample volume is mainly caused by the closure of seepage path.The key to the permeability and pore pressure dissipation rate of clay sand during penetration and hydrophobic consolidation is the content of capillary water in the pores,and all three meet the power function relationship with confining pressure.Taking the coal mining of a working face in the first mining area of Guotun Coal Mine as the research object,considering the combined action of the coal mining of thick topsoil and thin bedrock strata and the bottomed confined water hydrophobic consolidation settlement,the self-made high confined hydrophobic water bag is used to simulate the bottomed confined water hydrophobic consolidation settlement,then,the simulation test of similar materials was carried out.The characteristics of the destruction and collapse of the overlying bedrock and the characteristics of the bottom confined water hydrophobic,internal movement and deformation law of bedrock and thick topsoil during the mining of thick overburden and thin bedrock are studied.The deflection mechanism of the vertical shaft under the combined action of the near-distance and asymmetric mining of the thick topsoil and the thin bedrock and the bottomed confined water hydrophobic is revealed.The research results show that within the "three zones" of the whole bedrock section,a large number of horizontal and vertical cracks are formed near the two waists of the trapezoidal collapse arch due to the cantilever action of the rock layer,and spread to the bottom of the topsoil layer,leading to the hydrophobic sedimentation of the bottome aquifer.The bottom aquifer hydrophobic settlement has little influence on the movement and deformation of the rock in the bedrock section.The maximum subsidence and the maximum horizontal movement of the second aquiclude of thick topsoil increase obviously with the bottom aquifer hydrophobic settlement,and the subsidence boundary and the horizontal movement boundary have extended to the outside of the mining area by nearly double.With the increase of the hydrophobic content of the bottom aquifer,the surface soil will overturn towards the center of the sinking basin,and the shaft then deflected toward the asymmetric mining working face,and the deflection increases with the increase of the hydrophobic content of the bottom aquifer.Based on the surface subsidence and movement characteristics of thick topsoil and thin bedrock mining,for the first time,the soil-water coupling effect of the confined water during the subsidence of the thick topsoil is considered in the model of the thick topsoil and thin bedrock strata subsidence,and established and solved the surface subsidence prediction model under the combined action of coal mining and bottomed confined water hydrophobic settlement,explored the influence rule of the bottom aquifer’s hydrophobic properties on surface subsidence and horizontal movement,and obtained model tests and field subsidence data verification.The research results show that the surface subsidence curve caused by coal mining alone is of the shape of "small opening V",the surface subsidence curve caused by bottom aquifer hydrophobic is of the shape of "large opening V",and the surface subsidence curve under the combined action of coal mining and bottom aquifer hydrophobic is of the shape of "middle small opening V and both sides large opening V".The degree of surface subsidence is mainly affected by the thickness of bottom aquifer and the maximum waterhead drop value of bottom aquifer,while the range of surface subsidence and horizontal movement is mainly affected by the hydrophobic influence radius of bottom aquifer.A comparative analysis of the theoretical calculation solution and the field measured results shows that the error between the theoretically calculated maximum subsidence value and the measured maximum subsidence value is less than 4.0%.It can be seen that the theoretical model is of guiding significance for the prediction of the movement and deformation of the overlying strata caused by mining under thick topsoil and thin bedrock.Taking the shaft deflection of Guotun Coal Mine as the engineering background,through the comprehensive analysis of the hydrogeology of the mining area,the dynamic monitoring results of the mine water inflow and water level in bottom aquifer,the subsidence model of thick topsoil and thin bedrock stratum obtained in this paper is used to carry out the inversion calculation of the surface subsidence and shaft deflection under the separate mining action of 13 working faces in the first mining area of Guotun Coal Mine,the combined action of mining and bottom aquifer hydrophobic,the main cause of shaft deflection were obtained,and the stress state and safety of the existing deviated shaft were evaluated.The research results show that;under the action of coal mining alone,the industrial square is located outside the 10 mm subsidence contour,and the mining of each working face has almost no direct impact on the shaft deflection.Under the combined action of coal mining and bottom aquifer hydrophobic,the convergence of surface subsidence on the outside of the mining area is significantly reduced,the industrial square is located within the range of the 300～600 mm subsidence contour.The error between the shaft deflection inversion result and the measured result is less than 6%,which indicates that the prediction model has a high accuracy for the shaft deflection inversion,the deflection of the shaft in Guotun Coal Mine is caused by the combined action of coal seam mining and bottom aquifer hydrophobic.Figure[96]Table[33]Reference[140]... |
