Research On Movement Of Overlying Strata And Strata Behaviors With Cemented Backfilling Mining In Coal Mine

Based on the cemented filling technology of coal mining, this paper is to compare the cemented filling technology of coal mining with caving method through the study of overlying strata movement and strata behavior under different filling ratios on account of analogous simulation experiment as well as numerical simulation. This paper puts forward the asymptotic S-shaped beam model and gives a theoretical analysis to its formation conditions on the basis of comprehensive analysis of deformation law of overlying strata movement filled by cement Thanks to the theory of beam on elastic foundation, this paper shows the asymptotic S-shaped beam model and derives the formulaof mine area with technology of cutting and filling, and of abutment pressure and roof convergence. At the same time, calculation and analysis have been conducted in this paper. The author has put this theory into practice in the field of predicting and computing of surface subsidence and studies the coefficient values ofsuriace subsidence. The framework of control system of cemented filling quality has been constructed and the rationality and superiority of cemented filling used in Xiaotun Mine has been verified through technological effect and efficiency analysis. The fields this paper studies are as follows:(1) We can know from the analysis of cutting and filling under different filling ratios and caving method through analogous simulation experiments that:① Compared with the caving method, the overall structure of overlying strata used with cutting and filling is not damaged. When the filling ratio is 80%, the overlying strata used with cemented filling will curve and bend as a whole. Fissure zone and curve subsistence zone appear onlyin limited area nearby the main roof and no penetrable fracture appears in vertical stratum. When the ratio is 90%, curve subsistence zone appears only. The filling ratio of gob places great influence on the stability of overlying strata used with cutting and filling, which means that with the increase of filling ratio,the movement and destruction ofoverlying strata changes from separated strata, fracture to the curve subsistence as a whole, settling velocity and deflection of overlying strata will decrease dramatically.② The higher the filling ratio is, the lesser the deflection of roof will be, which means that the bearing capacity of filling body and top is higher, the stress concentration ratio of the ahead coal is lower. The smaller the area of supercharger is, the lower the stress decreases ratio of backward coal will be, and the smaller the area of decompression will be.③ Compared with caving method, the bigger the periodical roof weighting step of working face of cutting and filling is, the longer the period will be. The strength of periodical roof weighting will be inconspicuous. The higher the cutting and filling ratio is, the bigger the step of periodical roof weighting will be, the longer the period will be and the lower the strength of periodical roof weighting will be. With the increase of cutting and filling ratio to 90%, the change of pressure and periodicity will be inconspicuous.④ When it comes to the cemented filling, the interactions of filling body with surrounding rock could be seen from the following description. First of all, as geological material, the filling body could fill the surrounding rock immediately in an effort to maintain the integrity and bearing capacity of mining area and the surrounding rocks, and to enhance the capacity of roof to resist deformation and damage. Secondly, with the extending of mining area, the bearing system consisting of coal, filling material and surrounding rock prevents the overlying strata from further deforming. Thirdly, this bearing system changes the stress state of the whole mining area, which makes the area bear tri-axial stress instead of two-way stress. All of that will be helpful to stop the depression of overlying strata. The underground pressure of whole mine will decrease obviously due to the limited movement of overlying strata.(2) On the basis of analysis of characteristic of overlying strata movement in mining area used with cemented filling, the author puts forward the theory of asymptotic S-shaped beam and makes the mechanical model of asymptotic S-shaped beam on elastic foundation. The analysis is as follows:① The author makes the mechanical model of asymptotic S-shaped beam and puts theoretical analysis on the complete continuity condition and effective continuity condition, the formation condition of asymptotic S-shaped beam.② On account of the theory of beam on elastic foundation and without considering the face width and bracket, the main roof could be seen as semi-infinite beam so as to create the mechanical model of asymptotic S-shaped beam used with cutting and filling. Thanks to the model, the author derives the mechanics equations and the abutment pressure formula of coal area and filling area used with cutting and filling. The author also analyzes the distribution situation of abutment pressure in coal area and filling area. Firstly, with the extending of mining area, the vertical stress on one side of coal will decrease gradually to the stress of natural rock. Secondly, the vertical stress beard by filling body will increase with the extending of coal area and in consequence the vertical stress will also decrease to that of natural rock. When X equals 0, the counterforce of roof will be discontinuous and break. In the place where X equals 0, the stress of coal becomes the highest, while that beard by filling body becomes the lowest.③ On the basis of Xiaotun Mine, the author calculates and analyzes the factors influencing abutment pressure when the calculation parameters are clear. Firstly, the pressure of mining will be higher with the mining depth increasing. Secondly, the deflection and elastic modulus of filling body will put a comparatively obvious influence on the pressure when the roof touches the filling body. Thirdly, whenthe filling ratio is less than 85% orthe elastic modulus of filling body less than 0.3GPa which means the filling effect is not quite good, the effect of filling on reducing the underground pressure will be decreased dramatically.(3) Basing on the geological condition of pilot mine, the author employs the FLAC3D, a kind of numerical simulation software, to conduct the numerical simulation analysis on the movement law of overlying strata and the surface subsidence under the condition of different filling ratio and the elastic modulus of filling body. Moreover, the author conducts simulation analysis on the varying law of forward and backward pressure in working area with the extending of area. Here are the conclusions:① The filling ratio of gob places some influence on the abutment pressure of ahead working area used with cemented filling. When the ratio is 95%, the peak value of abutment pressure will strike the lowest and with the decrease of filling ratio, the peak value of abutment pressure will increase gradually. When the ratio is between 80% and 95%, the change of filling ratio places less influence on the abutment pressure.② The distribution trend of abutment pressure in the open-off cut is similar to that in area around the wall. But in contrast with the area around the wall, the peak value of abutment pressure in open-off cut is 20% higher than front abutment pressure and increases with the decrease of filling ratio. The influence scope of abutment pressure in open-off cut is larger than that of ahead working area and the value of abutment pressure far-end will decrease to that of natural rocks.③ The vertical stress of filling body in gob will increase with the growth of elastic modulus of the filling body, so does the increased scope of vertical stress.④ The ground deflection and slant deformation used with cemented filling will decrease with the increase of filling ratio and modulus of elasticity of filling body. Whenthe elastic modulus of filling body is 0.5GPa and the filling ratio is 85% or above, orthe filling ratio is 90% andthe elastic modulus of filling body is more than0.3GPa,surface slant value is in the allowance range of surface building damage level I.⑤ With the growth of filling ratio, the abutment pressures of ahead working area and filling body will decrease. When the cementedfilling used, the abutment pressures of ahead working area and filling body will increase at first, and then fluctuate in a certain scope. The higher the filling ratio is, the more inconspicuous the periodicity will be.(4) The author also analyzes the factors causing surface subsidence and computes the depression of roof Meanwhile, the author predicts the surface subsidence.① Using the flexure depression formula of roof derived, the author computes and analyzes all factors causing the depression of roof and rock beam. Key factor affecting the deflection is the one appears in the touch between coal depth and filling body. At the same time, the elastic modulus of filling body and that of coal also influence the deflection.② The author makes the surface subsidence prediction model on account of probability integral method and studies the coefficient value of surface subsidence in the use of numerical simulation Through the analysis of relationship between surface subsidence coefficient and equivalent mining height of cutting and filling, the author predicts and verifies the formula----q=0.009e3-622Mc, the relations between surface subsidence coefficient using cemented filling and equivalent mining height in Xinyang Mine. This method will also work in other mines employing cemented filling.(5) Relying on the spot of cemented filling in Xinyang Mine and on the basis of brief introduction of high-concentration cemented filling system, the author analyzes the factors affecting the quality of cemented filling, constructs the framework of cemented filling quality control system, makes a conclusion on the major measures to improve cemented filling quality and makes a detailed study on the key technology contained in the framework system.(6) According to the theoretical research result, the author gives a introduction to the geological condition and technology of cutting and filling in Xiaotun Mine in the process of industrial test of cemented filling in Xiaotun Mine. The author also supervises and analyzes the filling body stress and support resistance of working area and the movement of roof and the surface subsidence after filling in the Xiaotun Mine. Finally, the result shows that there is no obvious periodical roof weighting in cutting and filling, and that the abutment pressure decreases obviously which only accounts for 65% of caving method pressure. The effect of surface subsidence control is quite good which gains great social and economical efficiency. Moreover, the author presents some advice in terms of specific problems appearing in the project.