Study And Application On The Distribution Law Of Old Goaf Residual Cavity And Void

Residual cavity and void is the main factors affect the stability of buildingfoundation over old goaf. The distribution law of old goaf residual cabity, void isstudied, and the prediction model of old goaf residual movement and deformation isestablished in this paper, which has important theoretical and practical significance forold goaf foundation stability evaluation, harmful gas distribution, coal seamself-ignition, carbon monoxide overflow, groundwater movement etc.. In this paper,by experiental data analysis and theoretical derivation, the spatial structure types ofold goaf overlying strata are established, and the distribution law of old goaf residualcavity and void is analyzed, the prediction formula of residual cavity,void for variousspatial structure types of overlying strata are built. Furthermore, the modified modelof probability integral method is established by theoretical analysis, and theparameters selection principle is given at the same time. Finally, the prediction theoryand method of old goaf residual movement and deformation are set up based on oldgoaf cavity and void and the modified model of the probability integral method. Inthis paper, the main research results and innovations are as follows:1) Based on the relationship between cavity and coal pillar, in the plane direction,the overburden structure tpyes of old goaf are divided into three basic types:“”,“工”,“伞”.According to the strata structure and properties, in the vertical direction,each type can be divided into:(1) overlying strata being loose rock and soil(soil,weathered layer etc.);(2) elastic foundation beam with both ends located at the coaland rock pillar and the suspended middle;(3) voussoir beam;(4) elastic foundationbeam with both ends located at the coal and rock pillar and the middle at caving rock.2) Three preconditions for voussoir beam are studied, including: the maximumallowed inclination of rock, the maximum effective height (mining thickness andimmediate roof broken increase difference), immediate roof thichness.3) According to the measured data of borehole data, this paper summarizes andanalyzes the distribution law of old goaf residual cavity and void in the horizontaldirection and verdical direction, analyzes and builds the relationships of the work-faceborder distance with the ratio of cavity and void volume to mining thickness, and setsup the theorical and simplified calculation formula of old goaf residual cavity andvoid with “”,“工”overburden structure type. Besides, the broken rock’sexpansion coefficient, stress-strain relationship and calculation method are analyzed based on the broken rock circle hypothsis theory which is constructed in this paper.4) The modified model of probability integral method is constructed for surfacemovement and deformation by the principle of probability integral method, that theweighted value(1,-1/t1,1/t2) of movement and deformation are caused by miningwith three different major influence radius(r1, R1, R2). Then, the selection criteria andmethod of the parameters in the modified probability integral method areestablished.5) The prediction model of old goaf residual movement and deformation are setup based on old goaf cavity and void and modified model of probability integralmethod, and its parameters selection basis and method are studied in this paper. Then,the residual movement and deformation law are summarized and analyzed for thesemi-infinite old goaf with different coal pillar width and different goaf width.Meanwhile, example application is studied about residual movement and deformationof old goaf and the surface movement law of the adjacent work-face exploitationaffected by old goaf residual cavity and void.