Optimization of mining column recovery sequence under high stress conditions of an iron mine

The deep deposits are under high stress conditions. As the mining progresses, the stress field will be redistributed and stress concentration will occur, causing deformation and damage to the roof and surrounding rock masses, which will lead to large-scale engineering disasters, causing casualties and property. loss. The ground pressure activity is closely related to the mining method, the stope parameters and the mining order. Among them, the mining sequence has a great influence on the redistribution of the stope stress [1].

A reasonable recovery sequence helps to maximize the release of energy for excavation and accumulation of rock masses, and improves the stress distribution of the rock mass around the roof and the pillars, which is beneficial for preventing large-scale sudden ground pressure activities.
In addition, due to the existence of compressive stress concentration zone in the pillar, the pre-production process also destroys the pillar structure to a certain extent, which leads to difficulties in mining at a later stage. Therefore, the rationally designed sequence of pillar recovery is the key to safe and efficient mining of mines [2] ]. In this study, a study of iron ore, in combination FLAC3D software, numerical simulation analysis of the ore mining column order, stress and displacement by the following sequence comparison of different mining conditions generated optimized selection of the pillar mining sequence.
1 numerical model
1.1 Numerical simulation scheme design
A deep mine is mined by a staged empty field and a backfill method. The ore body is divided into sections and a column is placed in the section of the disk. The stope is divided into two steps of mining and mining, returning to the mining room and then back to the mining column. In order to meet the requirements of mining production capacity of deep and thick ore bodies, the number of stope mining at the same time is relatively high. Therefore, the mining sequence includes three trends along the ore body's tendency, direction and extent. This study only performs numerical simulation analysis along the tendency mining order, so the conclusions obtained are only applicable to the mining along the ore body and along the panel mining [3]. In view of the mining recovery, the existence of the pillar effectively guarantees the stability of the ore body. Therefore, the numerical simulation scheme of this study mainly considers the mining sequence of the mine after the end of the mining and the filling of the pillar. A total of three schemes have been developed ( Table 1), the layout of the stope in the panel is shown in Figure 1.

1.2 Constitutive model and orestone mechanical parameters The ore rock is brittle hard rock with good stability and integrity. Under the action of deep high stress field, the excavation of the stope will cause stress concentration in the surrounding rock of the empty area. The surrounding rock will enter a plastic state. Therefore, the constitutive model of the numerical calculation of this study selects the elastoplastic model, using the Mohr-Coulomb criterion [4-6]. According to the geological characteristics of the mine, the mechanical parameters of the ore obtained from the test were reduced. The results are shown in Table 2.

2 numerical simulation results
The numerical simulation analysis of the mining sequence of three different pillars was carried out. The maximum principal stress cloud map, the minimum principal stress cloud map and the vertical displacement cloud map after the excavation of the first pillar of the mine pillar are shown in Fig. 2, Fig. 3 and Fig. 4, respectively. Shown. The calculation results of stress and displacement after excavation in steps 1 and 2 are shown in Table 3.

(1) Analysis of stress distribution law. After the first step excavation, the maximum principal stress of the scheme I is the largest, the scheme II is the second, and the scheme III is the smallest, indicating that the scheme III has the lowest concentration of compressive stress; the tensile stress occurs at the top and bottom of the empty zone, and the tensile stress generated by the scheme III The maximum is 7.14 MPa, the second is the scheme I, and the scheme II is the smallest. After the second step of excavation, the maximum principal stress of the three schemes increased, and the values ​​were close; the maximum tensile stress of the schemes I and II increased compared with the excavation of the first step, but the maximum of the scheme III The tensile stress is lower than that of the first step, and the tensile stress is less than that of the schemes I and II.
It can be seen that the recovery sequence of the scheme III from the middle to the both ends of the panel, after the second step of excavation of the surrounding rock stress redistribution, the tensile stress concentration of the roof of the stope is effectively controlled, and the roof stability is optimal.
(2) Top plate displacement analysis. The displacement of the top and bottom of the stope is large, and the maximum vertical displacement occurs at the roof of the stope. After the first step, the vertical displacement of the scheme III is the largest, and the scheme II is the smallest. After the second step, the vertical displacement has a large increase. At this time, the vertical displacement of the scheme II is the largest, and the scheme III is the smallest. It can be seen that after excavation of the pillar, the vertical displacement of the roof of the stope in the middle part of the panel is larger than the vertical displacement of the roof of the end of the panel. Scheme III is the order of recovery from the middle to the ends of the panel, for the second step of excavation. The maximum vertical displacement afterwards also has a certain control effect.
3 Conclusion
Taking an iron ore as an example, three feasible pillar recovery schemes are proposed from the perspective of controlling the ground pressure, and the numerical simulation analysis is carried out by using FLAC3D software. It is considered that the rock mass stress during the second step excavation When the displacement and the displacement are greatly increased, the recovery order of the scheme III from the middle to the both ends of the panel can reduce the stress concentration of the roof, the tensile stress and displacement generated by the roof are the smallest, and the stability of the stope is the best.

references
[1] An Long, Xu Shuai. Study on design and optimization of mining sequence of deep thick ore body [J]. Journal of Northeastern University: Natural Science Edition, 2013 (3): 1642-1646.
[2] Guan Jialin, Luo Zhouquan. Numerical optimization of the mining sequence of the isolated pillars in the panel [J]. Mining Research and Development, 2012, 32(3): 18-21.
[3] Guo Li, Wu Aixiang. Numerical simulation analysis of mining sequence of Dongguashan deposit [J]. Chemical Minerals and Processing, 2002, 34(11): 10-13.
[4] Chen Yumin, Xu Dingping. FLAC/FLAC3D Foundation and Engineering Examples [M]. Beijing: Water Resources and Hydropower Press, 2009.
[5] Peng Wenbin. FLAC3D practical tutorial [M]. Beijing: Mechanical Industry Press, 2007.
[6] Wang Hao. Slope stability analysis based on Mohr-Coulomb criterion [J]. Modern Mining, 2016 (1): 196-198.

Article source: "Modern Mining"; 2017.1

Author: Li Peng with Hu Wei; Sinosteel Maanshan Institute of Mining Research Co., Safety and Health, State Key Laboratory metal mines, Hua Wei metal mineral resource efficient recycling of National Engineering Research Center Co., Ltd.

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