Study On Mining-induced Movement Regular Of Overlying Strata And Spatio-temporal Prediction In Surface Subsidence Under Thick Unconsolidated Layer

The problems caused by mining have a long history,especially in colliery.Under different geological conditions,mining subsidence problems caused by a series of coal extraction are complicated.Mining subsidence phenomenon induced by large scale coal mining under the geological of alluvium is more and more serious.So it is hard to predict the surface subsidence area,subsidence magnitude and subsidence sites from the aspects of time and space.Meanwhile,it significantly affects the characteristics and laws of overburden rock fracture field,displacement field and stress field.The heavy subsidence in coal mine has seriously influenced safe mining,recovery rate,meanwhile,given rise to the destruction of ecological environment.Therefore,the paper studied three main contents which were the rules of ground surface movement and deformation,overburden rock migration regular,the interaction between filling body and surrounding rock in roadway along the goaf.These researches can improve the yield of coal resources,extend the production time of colliery,prevent or reduce the mine geological hazards,promote the coal industrial security,scientific and sustainable development,and the benign ecological cycle in coal mine area.In fact,the phenomena of mining subsidence are the representation of strata movement spreading to the surface,Also the strata movement is produced by the surface subsidence motivation and incentive.Therefore,the paper in-depth study and explore mining strata movement and fracture development regularities and stress-strain characteristics from the source and mechanism to study the surface movement deformation law.The research background is based on the 3rd extraction section,Yunjialing coal mine.The geological and mining conditions are listed as followings: 90 m to 150 m thick alluvium,No.2 coal seam whose thickness is about 4.2m to be extracted,17° coal seam inclination.Through comprehensive research methodologies of field surveying,theory analysis,laboratory test and numerical simulation,the paper systematically studied the underground stope wall rock stress and strain regularity,overburden deformation and fracture field development,and surface movement deformation and subsidence caused by coal excavation,which has realized the stope-overburden-surface collaborative research.The mainly carried out the following works:In terms of law of surface subsidence under thick loose bed,the paper layout thesurface movement observation station to systematically monitor the surface subsidence caused by coal mining in 12303 working face and 12305 working face of Yunjialing mine the third coal mining area.During the process of subsidence eleven leveling measurements were implemented besides five times comprehensive surveying.This paper analyses the might affects made by surrounding work face.Based on field measured data,the paper analyzes subsidence,inclination,curvature,horizontal mobile end-state subsidence and horizontal deformation characteristics of line Z and line U after the two working faces mining,determines the final state surface movement and deformation angle parameters;analyses the surface dynamic mobile deformation characteristics of line U and line Z after the two working faces mining,determines the degree of working face advancing relation with the location of the maximum ground sinking points;studies the law of the changes of the surface subsidence velocity after the two working faces mining,calculates the maximum subsidence velocity lag distance,maximum subsidence velocity lag angle,advance distance and impact angle in advance;determines the formula of the maximum ground sinking speed through regression analysis.The paper comparatively analyses the differences of the surface subsidence rule of thick loose bed areas of Yunjialing mine with Xuhuai mine and Kailuan mine,such as from subsidence basin boundary angle,maximum angle of sinking,sinking coefficient,etc.Then the paper gives the internal causes of the differences between them.In terms of along the empty-filling body stability and deformation law of surrounding rock of roadway surrounding rock,the downhole field measurement was carried out.The paper observed the borehole imaging of the mine 12307 face ventilating roadway and haul roadway by the borehole imaging device.Thesis obtained under the influence of mining part overburden damage status and the developmental characteristics of fissure field;carried out the field monitoring of along the goaf roadway surrounding rock stress-strain-filling body,obtained the law of along the goaf roadway and return roadway deformation and stress distribution,filling body deformation and load distribution and internal stress transfer.Monitoring results show that the amount of floor convergence is generally greater than the amount of roof subsidence under the influence of a mining working face.At the same time,roadway roof strata was affected larger,and the main scope is roadway roof surface within 2 m.During the period of retention of roadway,overburden of roadway roof was broken,and the main roof subsidence effect on roadway roof subsidence and strata is bigger.Thiscaused severe deformation of roadway surrounding rock,roadway roof fracture made further development,further broken rock strata caused by level,further open and development of deep rock mass cranny,ventilating way corresponding shipping lanes in the same position more broken roof,roof deformation increase.Under the influence of the second mining working face,the residual return air roadway surrounding rock abutment pressure and the abutment pressure overlay each other,this section roadway surrounding rock stress leads to increased sharply.This increases the damage of the roadway roof,makes the shallow strata of roof fracture broken.Furthermore,it caused roof fracture more widely,and the roof abscission layer made the convergence deformation of roadway more greater than that caused by the first mining.The mainly scope of convergence of roadway deformation is within 4 m,however beyond the scope was less affected.The monitoring stress data of filling body inner is 5 MPa,but most of the stress does not exceed 4.2 MPa which is the filling body experiment strength.The filling body has the transverse deformation and vertical deformation,but it was not damaged.The transverse deformation of filling body performance was obvious only in local.The filling body made full use of the anchor reinforcement,so it had good integrity.At the same time,the goaf coal gangue and the roadway side point pillars changed the stress of filling body,improved the stability of filling body.So,the filling body has good adaptability to the roof and better support effect to the roof.Through the research,improving the state of surrounding rock bolting can reduce deformation of roof,and provide theoretical reference and technical support of the test coal mining area along the goaf follow-up retain roadway support,design,parameter optimization and implementation of the scene,and provide technical support for efficient retain roadway.In the aspect of overburden rock migration rule,this paper carried out physical simulation experiment on the basis of the ratio of similar material experiment.This experiment adopts a variety of monitoring means and methods,including optical fiber grating sensor,the close shot photogrammetry and 2D-DIC.The paper studies the strata movement rule and the subsidence mechanism of Yunjialing coal mining,and cross validation were carried out for the above monitoring methods.The author laid two similar models on an experimental platform,in order to facilitate the movement of the strata deformation analysis of characteristics and development rule of the fracture field differences reflect the result of the experiment.Model 1 and model 2,thickness of coal seam mining,the number of formation rock size are the same.The only difference is the key position,in order to reflect key stratum in the process of strata subsidence ofdifferent field and height control.Each model of the experimental results shows that the key-strata has significant control effect.The main key-stratum and its subsidence had a close relationship with the model position itself.Caving height and crack development degree of overlying strata are associated with critical layer thickness and strength of itself on model.Four kinds of monitoring methods had their own advantages and high accuracy in monitoring.Among them,the fiber Bragg grating sensor which was used to monitor the peak curve could be used as the basis of key strata fracture and 2D-full time domain of the DIC could obtain the dynamic research area displacement field and deformation field.This paper afforded a new technical methods for similar material simulation experiment.The paper used FLAC3 D finite difference program to optimize the different filling body sizes,and do numerical simulation for the macro pressure appear of stope.Through the simulation,mine adopts the most economical way of retained roadway under the condition of guarantee of normal roof bolting.Results show that the main show of goaf floor is shear failure and the main show of central region is shear tensile fracture after the working face mining.The maximum shear failure depth is about 30 m below the mined-out area.The major influence scope of the lateral support pressure is the side of goaf within 10 m,its main show is shear failure.After the next extents working face mining,the big and small structures of high stress were formed by the side of coal,the filling body and the protection coal pillar of the last extents working face.When the width of high water material filling body is 3.0 m,bearing performance of the filling body is higher during the period of retention of roadway.The synergistic effect between the filling body and the surrounding rock of roadway is high.This is advantageous to the change of strata damage status and damage to the surface deformation.When the width of high water material filling body is 2.5 m or 2.0 m,bearing performance of the filling body is lower during the period of retention of roadway.The deformation of the filling body was large,and the stability was poor.The control of roadway surrounding rock was harder.After finishing high water material filled along the goaf to retain roadway,removal of the roof near the goaf side at the appropriate time is beneficial to keep the stability of surrounding rock of roadway.In terms of surface subsidence prediction and parameter inversion of time and space,the paper presents a dynamic time normal distribution function is adopted to improve the surface subsidence prediction,builds the mathematical model of surface subsidence dynamic prediction based on the normal distribution function of time,analyses of the influences of curve shape coefficient on the prediction accuracy and normal distribution time function completeness of space and time,confirmed the mathematical model in the earth's surface sinking,sinking velocity and acceleration is consistent with the spatial and temporal variations of surface subsidence process.For Yunjialing coal mine irregular surface movement observation station,the paper uses the space curved surface fitting method to calculate the expected surface subsidence parameters and time parameters.The paper on the basis of field monitoring data are analyzed and validated,the project was verified with the measured data of Yunjialing coal mine and the measured data of Xinzhi coal mine.The result shows the model prediction precision meet the demand of engineering,and the surface subsidence prediction model based on normal distribution time function can be thick loose bed under the condition of surface movement and deformation prediction was confirmed.Based on the prediction model,the paper used of Matlab platform to developed friendly interface,timely mapping of surface subsidence prediction information system.The system contains the point prediction module,the line is expected to module,three-dimensional surface subsidence is expected to module and parameter inversion module.The paper can carry on the scientific forecast to the coal mining induced surface subsidence by the system.