0 preface
A mine in Jiangsu originally used the up-point column to fill the mining method. It not only has a top and bottom column, but also has a column and a point column. The total loss rate of the mine is generally about 20%. Under the condition that resources are increasingly scarce, it is necessary to transform mining technology to achieve the purpose of improving ore recovery rate and improving downhole operating conditions. Through research, the use of the staged collapse phase empty field post-filling mining method is adopted as the mining scheme of this type of ore body [1].
When the mining method is used in the empty field after the staged collapse phase, the first method is to use the empty field method to recover the mining, and then the filling is carried out after the mining. The stability of the stope is very important before the end of the mining to the completion of the filling body maintenance. It is very important to select reasonable parameters of the stope structure. It not only affects the production safety of the mine, but also has an important impact on the technical and economic indicators of the mine [2-5].
In this paper, FLAC finite difference software [6-8] is used to select the reasonable boundary conditions for numerical calculation of maximum tensile stress, maximum vertical displacement and plastic deformation under different stope structure parameters. According to the calculation results, a reasonable stope structure is determined. Parameters provide a theoretical basis for the safe and efficient production of mines.
1 numerical scheme
According to the occurrence characteristics of the ore body, the vertical ore body of the stope is arranged. The length of the stope is the thickness of the ore body, the maximum is 50m, generally 10~47m. The width of the stope is determined according to the stability of the ore body, which can be 10~20m. The height of the stope is the stage height, generally 50m.
According to the above-mentioned mining field division, six numerical models are designed to simulate the stability of the stope mining process under different stope structure parameters. The numerical model is as follows:
(1) Model I—the size of the stope (length × width): 30m × 10m, the exposed area of ​​the top plate is 300m2;
(2) Model II—the specification of the stope (length×width): 40m×10m, the exposed area of ​​the top plate is 400m2;
(3) Model III—the specification of the stope (length×width): 50m×10m, and the exposed area of ​​the top plate is 500m2;
(4) Model IV—the specification of the stope (length×width): 30m×15m, and the exposed area of ​​the top plate is 450m2;
(5) Model V—the specification of the stope (length×width): 40m×15m, and the exposed area of ​​the top plate is 600m2;
(6) Model VI———The specification of the stope (length×width): 50m×15m, and the exposed area of ​​the top plate is 750m2.
2 numerical model and rock mechanics parameters
For numerical simulation, a corresponding three-dimensional numerical model must be established. The calculation range of the numerical model must be large enough, and the calculation time, computer performance and simulation effect must be considered. The model size of this simulation is 500m×120m×600m. The three-dimensional numerical model is shown in Figure 1.
Rock mass mechanics parameters are the basic data for numerical simulation calculations. See Table 1 for the mechanical parameters of mine rock mass.
3 analysis of simulation results
3.1 Maximum tensile stress of the top plate
According to the FLAC numerical simulation calculation results, the maximum tensile stress of the top plate of the numerical models I, II, III, IV, V, VI is shown in Fig. 2 to Fig. 7.
Through the numerical simulation of the maximum tensile stress of the roof of the stope, when the mining simulation is carried out by the empty-field post-filling mining method in the staged collapse stage, the stress is concentrated in the middle and the end of the roof of the stope near the roof of the stope. When the width of the stope is 10m, the maximum tensile stress at the middle and end of the roof in the model I, model II and model III near the top of the stope is in the range of 1.1 to 2.2 MPa; when the width of the stope is 15 m, In Model IV, Model V, and Model VI, the maximum tensile stress at the middle and end of the stope near the top of the stope is in the range of 1.1 to 2.3 MPa.
3.2 vertical displacement of the top plate
According to the FLAC numerical simulation calculation results, the vertical displacement of the numerical model I, II, III, IV, V, VI top plate is shown in Figure 8 ~ Figure 13.
Through the simulation of the vertical displacement of the roof of the stope and the mining simulation of the empty field after the collapse of the mining process, the vertical displacement of the stope increases with the increase of the span of the stope, and the middle and end of the roof of the stope are close to the mining. The vertical displacement at the top of the field is the largest. When the width of the stope is 10m, the vertical displacement of the middle part and the end of the top plate of the stope near the stope of the model I, the model II and the model III are both 0-1.1cm, and the displacement is small; when the width of the stope is 15m In the model IV, model V, and model VI, the vertical displacement of the middle and end of the roof of the stope near the top of the stop is 2.1~4cm, and the displacement is large.
3.3 Plastic damage zone
According to the results of FLAC numerical simulation calculation, the distribution of plastic failure zones of numerical models I, II, III, IV, V and VI are shown in Figures 14 to 19, respectively.
Through the numerical simulation of the plastic failure zone of the roof, and the mining simulation of the empty-field post-filling mining method in the staged collapse stage, the range of the plastic zone of the stope gradually increases with the increase of the span of the stope, mainly due to shear failure. In the middle and end of the roof of the stope, near the roof of the stope. When the width of the stope is 10m, the plastic zone of the stope in Model I, Model II and Model III is less, and the damage range of the stope is obviously small; when the width of the stope is 15m, Model IV, Model V, Model VI The plastic zone in the middle stope has a large distribution and a large range, mainly concentrated in the end of the stope near the top, and the stope has undergone major damage.
4 Conclusion
Through the above numerical simulation, comparative analysis of the simulation results of each scheme model, the following conclusions can be drawn:
(1) The mining of the ore body causes the stress to be redistributed, and the stress in the mining area is released and transferred. Stress concentration occurs locally in the roof of the stope, which will cause damage to the roof of the stope;
(2) Through numerical simulation, it is found that the stress concentration area of ​​the stope is mainly distributed at the top and end of the stope near the top, and with the increase of the width of the stope, the increase of tensile stress is not obvious, but the vertical displacement and mining The range of field plastic zone is significantly increased. When the width of the stope is 10m, the range of the plastic zone is obviously less than the width of the stope of 15m, and the stability is relatively good.
(3) Through the above analysis, the width of the stope mining using the method of staged collapse ore filling in the open field mining method should be 10m, and the length of the stope should be taken as the thickness of the ore body.
references:
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[6] Liu Bo, Han Yanhui. FLAC principle, examples and application guide [M]. Beijing: China Communications Press, 2006.
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Author: Wu Feng Feng; Changsha Institute of Mining Research Co., Ltd., Changsha 410012;
Source: Mining Technology 2015, 15(5);
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