(1) The initial stress field is formed according to the self-weight stress, so that the model reaches the initial stress equilibrium state. (2) The research object is mainly for all the mining sites mined from the unexploited state to the second extension project of Meishan Iron Mine. The mining site mining model is constructed according to the characteristics of the sublevel caving method. The minimum principal stress is tensile stress in the roof of the ore body, which is finally released during the process of overburden collapse, and is the minimum in the area of ​​surface subsidence and collapse. In addition, due to the thick ore body, the ore body is buried shallow, the depth of mining and the thickness of the mining are relatively small. After the surrounding rock collapses, the surface shows obvious shear yielding area and tensile yielding area, and the surface collapse state is obvious, and with the recovery step The extent of the surface collapse has also expanded. At the end of the mining of the -420m layered ore body, the surface subsidence depth is 154.22m, and the plastic zone volume is 4.45×108m3. Pressed Bends,Qf Pressed Bends,Fb Pressed Bends,Pressed Bend 90° Short YANTAI DONGTAI STANDER OFFSHORE ENGINEERING CO.,LTD , https://www.dongtaicolumbus.com
1 Project Overview
Meishan Iron Mine is located in the northern part of the Mesozoic continental volcanic fault basin in Ninglang. The ore body is located in the contact fracture zone of the pyroxen andesite and the diorite, and is a large lenticular blind ore body. The highest elevation is -34m, the lowest elevation of the ore body is -524m, its plane projection is elliptical [2], the area is 0.8km2, the strike length is 1370m, the width is 824m, the average thickness is 134m, which belongs to the gently inclined thick ore body. . The main components of the ore are magnetite and hematite. The ore body has good stability and the surrounding rock is easy to fall. The occurrence of ore body is characterized by shallow burial in the southwest, deep burial in the northwest, and burial depth of the rich ore mainly in the range of -50 to -350 m. The lean ore is mainly at the edge of the ore body, and the rich ore and the lean ore are in a continuous transition relationship. Layered output. The content of TFe in the mining area is up to 66.06%, the average grade is 49.24%, the average grade of lean TFE is 32.93%, and the average grade of TFe in the whole mine is 39.14%.
Through on-site sampling and laboratory mechanical parameters experiments, the main ore mechanical parameters of the mine are obtained, and the comprehensive engineering geological characteristics are obtained. The mechanical parameters of the rock mass after the strength reduction are shown in Table 1. 
2 3D visualization of mining environment
The basis of the numerical simulation analysis of the steady state of the mine subsidence area is to realize the three-dimensional digitization of the mining area environment, and calculate by computer simulation. The three-dimensional digitization and visualization of the mining area is mainly based on the mining software to digitally reproduce and recognize the deposit environment, that is, to establish a virtual deposit of digital and three-dimensional display based on the true geographical coordinates of the mine [3].
2.1 Ore body digitization and 3D visualization processing
According to the existing profile map of the Meishan iron deposit, the 3DMine is used to spatially superimpose the elevation and plane coordinates of the section and the three-dimensional position, and the adjacent positions of the sections are sequentially stacked according to the layout plan of the exploration line. For the convenience of simulation calculation and clear graphic display, according to the ratio of 1:100, only some exploration line processing results are shown in the figure, as shown in Figure 1.
According to the ore body information of each exploration line profile, the entities between the sections are constructed to form a three-dimensional solid model of the ore body, as shown in Figure 2.
The formed three-dimensional solid model of the ore body is subjected to block processing to form an internal filled block model, and the block size is divided according to the ore body range, as shown in Fig. 3.
2.2 Mining area surface digitization and 3D visualization processing
According to the topographic geological map of the mining area, combined with the elevation information, the 3DMine mining software is used to three-dimensionally process the surface of the mining area. The topographic map is imported into 3DMine, and the Z information of each contour line is assigned according to the contour elevation information to form a three-dimensional contour map of the mining area, as shown in Fig. 4.
On the basis of three-dimensional contour lines in the mining area, a triangular mesh connection is used to form a three-dimensional surface of the mining area, and the surface information of the survey line profile is used to carry out three-dimensional reduction of the surface within the collapse range, as shown in Fig. 5.
According to the obtained three-dimensional three-dimensional map of the ore body and the surface, the three-dimensional block formation of data coupling is performed, and the three-dimensional surface processing is performed by adding constraints. The three-dimensional view after the block is shown in Figure 6.
Numerical Simulation Analysis of 3 Stable Area Stability
3.1 simulation steps
(3) Simulating the submerged rock movement and surface subsidence deformation state after the ore body mining by the bottomless sublevel caving mining method, and carrying out the mining simulation in the order from top to bottom, the recovery calculation of each step is in the previous step. Based on the calculation, it objectively reflects the superposition effect of the previous mining on the next mining, and records the surrounding rock stress and displacement state during mining.
3.2 Numerical simulation process
According to the sub-column sublevel caving mining method adopted by Meishan Iron Mine, the numerical simulation of underground ore body mining is carried out, and the movement and failure law of overlying strata is analyzed and analyzed, and then the stability analysis and zoning of the collapse pit without accumulating solid tailings are carried out. the study. In the simulation process, according to the actual mining practice, the height of -68~-88m is 10m, the height of -88~-112m is 12m, the height of -112～-138m is 13m, and the section is -138～-198m. The height is 12m, the segment height from -198 to -318m is 15m, the segment height from -318 to -330m is 12m, and the segment height from -330 to -420m is 18m. Through numerical simulation, the maximum principal stress cloud map, minimum principal stress cloud map and displacement cloud map of surrounding rock during each section mining process are obtained, as shown in Figure 7~12.
3.3 Analysis of numerical simulation results
According to the simulation results, during the process of returning to the ore body by the sub-column sublevel caving method, the changes of overburden stress, displacement and caving are gradually superimposed as the mining steps of the layered ore body are superimposed.
From the time of mining -100m ore body, the surrounding rock collapsed to the surface of the surface, forming a caving funnel. With the progress of the mining process, the expansion rate of the surface subsidence range is still small when the -186m layered ore body is recovered. When the ore body is recovered above -186m, the initial rock mass has a great influence on the original rock stress, and the secondary stress field gradually forms during the collapse of the surrounding rock. However, despite the redistribution of stress in the surrounding rock and the displacement of the surface, due to the small number of stratified ore bodies, the distribution range is small, the plastic range of the surface caving is relatively small, and the relative changes in several layers of mining and superposition process are relatively small. When the mining is completed, the surface subsidence depth is 12.14m and the plastic zone volume is 2.02×106m3.
When mining the ore body below -198m stratification, it can be obtained from each stress cloud map (Fig. 7, Fig. 9, and Fig. 11). The stratified mining results in the periodic subsidence and collapse of the overlying strata, and the secondary stress is overburdened. The rock layer is released and gradually reaches the surface. The maximum principal stress shows a difference in the surrounding rock of the ore body. The basic law is that the lower plate stress concentration is larger, but in the last -420m layered ore body mining and overburden caving After that, the maximum principal stress is basically symmetrically distributed on both sides of the overburden.
According to the representative stage diagrams of Figure 8, Figure 10 and Figure 12 and the whole simulation process, it can be seen that the overburden collapse and the displacement of the overlying strata correspond to each other during the numerical simulation. The surface of the south of the 403 exploration line is in the early stage of mining. The plastic zone appears, and the displacement increases to 7.42m. At this time, the subsidence pit has appeared on the surface, and the surface displacement and collapse range gradually increase during the mining of the -100～-186m layered ore body, but the southern surface plasticity The size of the area is above -186m, and all ore bodies remain basically unchanged after the end of mining, but the displacement of the west part of the collapse pit will increase during the subsequent mining. Therefore, the development of the surface subsidence area south of the 403 exploration line has basically stabilized, and there will be sedimentation inside the collapse pit.
The surface subsidence area of ​​the 403-402 exploration line gradually changed during the gradual recovery process, and it changed the most when the -198m layered ore body was recovered, showing a jump growth, mainly in the middle surface displacement, and on both sides of the east and west. In the subsequent layered mining process, the plastic zone range and surface displacement of the west surface gradually become larger, and the plastic zone volume gradually becomes larger.
The surface subsidence area north of the 402 exploration line has little change during the early mining process. When the -112m layered ore body is recovered, the northern surface plastic zone and displacement suddenly increase, the surface collapses, and the subsequent layered ore body recovers. The process gradually increases until the -366m layered ore body recovers, the surface plastic zone range remains basically the same, but the surface displacement is gradually increased until the end of the -420m layered ore body.
The corresponding relationship between the surface change area and the exploration line position is shown in Figure 13.
4 Conclusion
According to the mining environment and mining characteristics, the steady state analysis was carried out by the combination of three-dimensional digitization and numerical simulation analysis. The mining area collapsed in the vicinity of 403 lines and 402 lines, and the surface was divided into three basic areas. In the subsequent mining process, the south part of the 403 line has only the settlement inside the collapse pit, the surface collapse of the surface of the 403-402 line area will increase, and the surface subsidence of the area north of the 402 line will be the most obvious and will continue to increase until Eventually collapse the boundary. In the actual production of mines, surface safety management should be carried out according to the different characteristics of the surface of the mining area to achieve safe production.
references
[1] Lu Zhigang. Study on surface subsidence caused by ore body mining under complex high stress environment [D]. Changsha: Central South University, 2013.
[2] Chen Yong. Study on collapse and displacement mechanism of overlying rock mass in Meishan Iron Mine [D]. Xi'an: Xi'an University of Architecture and Technology, 2004.
[3] Li Guoqing, Hu Nailian, Chen Daogui, et al. Research [J] metal mine geological resources of digital building framework. Metal Mine, 2010 (4): 118-122.
Wang Xing, Sun Guoquan, Liu Hailin; State Iron and Steel Group Maanshan Mine Research Institute Co., Ltd., State Key Laboratory of Metal Mine Safety and Health, Huawei Metal Mineral Resources Recycling National Engineering Research Center Co., Ltd.;
Article source: "Modern Mines"; 2016.4;
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Numerical Simulation Analysis of Stability Status in the Subsidence Area of ​​Meishan Iron Mine
Meishan iron ore has been used Sublevel caving mining method, after decades mined different intensity, generated at the surface of different sizes and different periods subsidence area and moving area [1], and as the second phase and two During the extension project, the mining area will gradually increase, and the corresponding surface will further settle and collapse. In order to fully understand the collapse deformation law and steady state of the surface during the mining process, according to the characteristics of the mining method, according to the mining sequence, the combination of three-dimensional digitization and numerical simulation is used to analyze the stability status of the subsidence area of ​​the mining area, which is safe and efficient for the mine. provide assurance.