| In recent years,a new damage form of shaft deflection and vertical compression deformation in thick loose layer and thin bedrock stratum in Juye mining area,Shandong Province,is obviously different from the previous failure characteristics of shaft compression due to vertical negative friction,and its deflection damage mechanism is still unclear.Taking the shaft deflection of the main,auxiliary and air shaft in the asymmetric mining of thick loose bed and thin bedrock in Guotun mine as the research object,this paper analyzes the hydrogeological conditions,the failure characteristics of shaft deflection and the leakage causes of bottom aquifer in Guotun mine.Taking 1302 first mining face as an example,the indoor similar material model test of shaft deflection law under the joint action of thick loose bed and thin bedrock coal mining and bottom aquifer drainage is carried out,Based on the mining subsidence theory,soil consolidation theory,time function theory and the interaction theory between shaft wall and soil,the four-dimensional space-time calculation model of formation movement and deformation under the joint action of coal seam mining and bottom drainage and the shaft stress model under various loads are established.Combined with the field shaft deflection data,the theoretical model is used to inverse the shaft deflection,The mechanism of shaft deflection in asymmetric mining of thick loose bed and thin bedrock in Guotun mine is revealed,and the shaft safety is analyzed.The results show that:(1)The similar material model test shows that after the mining of the working face,the bedrock water conducting fracture zone develops to the bottom aquifer,resulting in hydrophobic consolidation settlement of the bottom aquifer;The settlement and horizontal displacement of loose layer caused by bottom water drainage aggravate the movement and deformation of loose layer caused by coal mining,accounting for about 36%and 25%of the total formation deformation;With the increase of bottom water content,the stratum subsidence boundary and horizontal movement boundary gradually extend to the wellbore.Finally,the loose layer disturbance caused by bottom water content will spread to the shaft,resulting in the shaft deflection to the asymmetric mining face,and the deflection will increase with the increase of bottom water content.(2)The theoretical calculation model of surface settlement and horizontal displacement under the joint action of coal seam mining and bottom water drainage shows that the surface settlement caused by bottom water drainage accounts for 15%?30%of the total settlement,and the surface horizontal displacement caused by bottom water drainage accounts for 10%?25%of the total displacement,and the influence range of surface settlement and horizontal displacement caused by bottom water drainage is about 80%relative to the influence radius under separate coal mining,Therefore,the drainage of bottom water not only aggravates the surface settlement and horizontal displacement,but also directly expands the range of surface movement and deformation,making the range of surface disturbance larger;Bottom aquifer thickness and bottom aquifer drawdown can promote surface settlement,horizontal displacement,settlement influence radius and horizontal displacement influence radius,and the influence range of surface horizontal movement is greater than that of surface settlement under any bottom aquifer thickness or bottom aquifer drawdown.(3)Considering the dynamic process of surface movement and deformation,based on the hypothesis of knoth time function model,a new model hypothesis is proposed that the settlement speed of a surface point at a certain time is directly proportional to the nth power of the difference between the final settlement value and the instantaneous settlement value of the point,and an improved knoth time function model is established,Based on the measured data of six monitoring stations on the main section of the subsidence basin strike of working face 1301 in Guotun mine,the accuracy of the traditional knote time function model and the improved knote time function model are verified.The results show that the surface subsidence value of the improved knote time function model is significantly higher than that of the traditional time function model.(4)Combining the improved knoth time function model with the stratum movement calculation model caused by coal seam mining and bottom water drainage,a fourdimensional space-time calculation model is established.The model is used to inverse the shaft deflection data of Guotun mine.It is revealed that the deflection mechanism of the main,auxiliary and air shafts of the mine is the superposition of bottom water drainage consolidation settlement caused by coal seam mining,The influence range of stratum settlement is enlarged,and its settlement mainly affects the tangent of angle tan ?2=0.6,far less than 2.41?3.54 specified in the specification.Because the main,auxiliary and air shafts are within the influence range of stratum settlement,under the condition of asymmetric coal seam mining(northwest direction),the deep loose layer moves horizontally in this direction,resulting in shaft deflection.(5)The theoretical calculation and analysis of the influence of bottom aquifer thickness,the thickness ratio of loose layer to bedrock,the drawdown of bottom aquifer level and the tangent of main influence angle of loose layer on wellbore deflection.The results show that the deflection of main and auxiliary wellbore increases with the increase of bottom aquifer thickness,the thickness ratio of loose layer to bedrock and the drawdown of bottom aquifer level,and decreases with the increase of the tangent of main influence angle of loose layer.The sensitivity of the above four influencing factors to wellbore deflection can be summarized as follows:drawdown of bottom aquifer level>thickness ratio of loose layer to bedrock>tangent of main influence angle of loose layer>bottom aquifer thickness.(6)The "upper plastic and lower elastic" shear mechanics model of the interaction between stratum and wellbore is established,the analytical solutions of vertical additional stress and bending stress of wellbore are deduced,and the stress characteristics of deviated wellbore are analyzed.The research shows that the bending stress caused by wellbore deflection is very small and can be basically ignored;The vertical additional stress gradually accumulates from top to bottom.At the junction of loose layer and bedrock,the total axial stress of main and auxiliary shafts exceeds its ultimate bearing capacity.However,because the shaft is embedded with compressible joints,the overlying pressure is gradually released with the deformation of compressible joints..Figure[85]Table[27]Reference[164]... |
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