Displacement monitoring and stability analysis of surrounding rock in deep mining of metal mine

With the depletion of shallow mineral resources, deep mining has become an inevitable trend in underground mining. In the deep mining process, the surrounding rock of the roadway and the stope is in the complex stress environment of high ground stress and high lava water pressure, and the stability is facing a great threat [1-2]. Displacement monitoring is an important way to evaluate the stability of surrounding rock, and it is a scientific method to reveal the deformation law of rock mass in mining stope. It is intuitive and practical in field application [3-4]. Metro Gold Mine has entered the stage of deep seabed mining, mining depth of more than 1000m [5]. During the deep mining process, the ground pressure is intensified, and the surrounding rock deformation, collapse, roofing, and gangs are increasing. Especially at the level below -600m, significant instability of the surrounding rock of the roadway has occurred, in order to solve the deepening of the new city gold mine. A series of problems occurred in mining, the establishment of deep mining displacement monitoring system based on a variety of monitoring methods, real-time monitoring of deep surrounding rock deformation in the mining area, comprehensive analysis of surrounding rock stability, revealing surrounding rock damage and deformation during deep seabed mining The law has important scientific and practical value for guiding the safe and efficient mining of deep mines.
1 roadway overview
Xincheng Gold Mine is a submarine mining and mining mine. The main factors affecting the stability of deep mining roadway are large soft structural planes such as F1 and F3 faults. The tunnel is located in the lower part of the F1 fault, and the northwest-oriented structure is relatively developed. The fault zone and nearby rocks are crushed and broken, and the block and collapse are easy to occur when excavating. The F3 fault strikes the northwest, and the dip angle is close to 90°. The rock in the fault zone is broken and is mainly filled with gravel, mudstone, kaolin , gravel and clay. The long-term immersion of groundwater makes it in a state of water saturation, which leads to a decrease in the friction between the particles of the filling body. When the -600m horizontal transportation lane is driven into the F3 fault, the sharp increase of the ground stress causes the deformation, collapse and accident of the surrounding rock of the roadway to increase. As the key transportation lane for deep mining of the stope, the stability of the -600m roadway (Fig. 1) is related to the safe production of the entire stope.

2 roadway surface displacement monitoring
2.1 Monitoring method
JSS30A telescopic type using the number of produced coal ASTRI Beijing well construction extensometer significant convergence of sides of the roadway, roof subsidence monitoring, measurement accuracy of the instrument is ± 0.1mm, reading accuracy of ± 0.05mm, The measured baseline is 0.5 to 15 m long. The specific measurement principle refers to the literature [6]. In this monitoring, there is a problem with the roadway in the northern section of the 600m horizontal roadway. The baseline layout of the specific roadway measurement section is shown in Figure 2.

2.2 Monitoring point arrangement

The Xincheng Gold Mine adopts the upward horizontal filling mining method [5]. The mining operation advances upwards, and the surrounding rock mass stress will undergo the process of “balance-unbalance-rebalancing”, and the steady state of the roadway will undergo obvious stages. In order to ensure the long-term and accuracy of monitoring, under the premise of fully considering the location of avoiding ducts and water pipes, ensuring the reading of instruments and normal monitoring, and the installation of the instrument does not affect the normal production of the mine, the monitoring points are set at -600m connecting the mining joints. Middle section of the roadway. It mainly includes 2 multi-point displacement monitoring points and 4 roadway section convergence measurement points. The specific locations of each measurement point are shown in Figure 3.

2.3 Cross-section monitoring results of each line
Fig. 4(a) and Fig. 4(b) show the convergence curve of the line at the measuring points of the 1# and 2# sections. The maximum deformation rate of the roadway during the whole monitoring period is 0.08mm/d, and the minimum is 0.04mm/d. From the 40th day of monitoring, the rate of convergence deformation of the line is increased by the influence of the main production stope at -600m level, but the variation rate of the convergence deformation rate is affected by the distance from the measuring point. Smaller, indicating that the stability of surrounding rock is less affected. After the end of mining, the maximum deformation rate of the surrounding rock of the roadway is 0.04mm/d, and the average deformation rate is 0.02~0.03mm/d. It can be seen that the stability of the surrounding rock in this area is mainly affected by the mining disturbance. After the field operation, the surrounding rock of the roadway near the measuring point is relatively stable.
Fig. 4(c) and Fig. 4(d) show the convergence curve of the line at the measuring points of the 3# and 4# sections. The measuring point is located in the middle of -600m, near the line 1830, north of the F3 fault. The roadway north of the F3 fault is gradually developed from south to north, so the displacement of the roadway is obvious here. The cumulative convergence of the AC line in 84d reached 3mm, which is more than 1mm than the maximum convergence of the 3# measuring point AC line. The deformation at the initial stage of monitoring is more severe, and there is a relatively obvious growth trend. With the passage of time, the growth trend is gradually slowing down, and the surrounding rock deformation tends to be stable. In the whole process of roadway excavation and mining, the surrounding rock deformation of the roadway has experienced three stages: the deformation increases sharply—the deformation grows slowly—the deformation is basically stable. At 120d, the deformation characteristics of the above three stages were well reflected at the monitoring point during the monitoring period of nearly 6 months.

3 roadway deep multi-point displacement monitoring
3.1 Monitoring method
During the deep mining process of the stope, under the influence of the disturbance stress, the surrounding rock will undergo different degrees of damage evolution process at different depths. The displacement of the rock mass at different depths can characterize the stability of the surrounding rock mass to some extent. Surface displacement monitoring has a certain degree of advancement [7-8]. According to the characteristics of large water inflow and complete rock mass in Xincheng Gold Mine, this monitoring adopts self-developed anchoring multi-point displacement meter. By setting measuring points at different depths of rock mass, real-time and continuous monitoring of rock stratum displacement can be carried out. The monitoring device mainly includes an inner tube, a disc, a measuring steel wire, a steel claw and a data transmission device. The displacement meter adopts a distributed network measuring system, which can automatically collect data and store it in a database according to the collection time sequence. The functions of data review, real-time display, and curve drawing can be realized through the monitoring system [9].
3.2 Monitoring point location
In this monitoring work, two multi-point displacement measuring points are arranged at the north and south ends of the -600m horizontal roadway (Fig. 2). According to the different depths of the rock mass, four monitoring points are arranged at each measuring point, and the depths from the surface of the rock mass are 20, 15, 10 and 5 m respectively, so as to realize the stereoscopic monitoring of the stability of the rock mass, and the cross-sectional arrangement of the multi-point displacement meter is shown in the figure. 5.

3.3 Deep multi-point displacement monitoring results
Figure 6 shows the displacement time curves of different depths of rock mass. In the first 40 days of the monitoring period, the average deformation rate of each measuring point is above 0.03mm/d, and the change is relatively stable. In the late 100d of monitoring, the displacements of different depths in the rock mass of each measuring point show a gradual growth trend. The average deformation rate is above 0.07 mm/d. Different measuring points are different, indicating that the rock mass damage in the stope presents a certain time and space difference. In time, the displacement of the rock mass gradually increases under the influence of mining, and finally stabilizes, indicating that the damage and damage of the rock mass has experienced the process of “stability-unbalance-re-stabilization”. Therefore, it should be avoided in engineering for a short time. Concentrated large-scale mining, timely support, shortening the unbalanced time of the rock mass, and making the rock mass re-stabilized quickly; in the space, under the influence of the same mining, the displacement of the shallow rock mass is relatively large, and the deep displacement is relatively small, 1# The variation of the displacement of the whole rock mass at the measuring point is not much different. The displacement of each measuring point in the rock mass of the 2# measuring point is quite different. This is because the 2# measuring point is close to the F3 fault, and the short-term concentrated mining operation is shallow. The displacement of the rock mass is faster and the displacement in the deep part is relatively stable, indicating that the shallow rock mass in this area has been broken. It should prevent the safety hazard caused by the fall of the pumice stone , and timely use the anchor spray support to enhance the self-supporting force of the surrounding rock. Ensure mining is safe.

4 Conclusion

(1) Structural planes such as faults are the internal factors affecting the stability of deep mining roadway. Mining disturbance is an external factor affecting the stability of roadway. The mining activity near the fault in the 600m stope has a great impact on the stability of the stope. Avoid large-scale centralized mining near faults, rationally optimize the mining sequence, and ensure mining safety.
(2) Through monitoring, it can be seen that the mining activities have experienced the process of “stability-unbalance-re-stabilization”, and the deformation of the roadway has experienced three stages: “rapid growth—slow growth—basic stability”. Therefore, the mining process The medium should support the stope rock body in time, shorten the unbalance time of the rock mass, improve the self-supporting force of the surrounding rock mass, and keep the roadway stable.
(3) In the process of damage evolution of the stope rock mass, there is a strong spatial and temporal difference. In general, the deformation of the deep rock mass during the mining process is smaller than that of the shallow rock mass, and the deformation of the roadway after the shallow surrounding rock breaks. It will increase sharply and the stability will be greatly affected. It is necessary to timely support the roadway and fill the stope to ensure safe and efficient mining.

references
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[3] Liu Gao, Wang Xiaochun, Nie Dexin. Characteristics and evolution mechanism of surrounding rock stress field of underground roadway in Jinchuan mining area [J]. Geological Hazards and Environmental Protection, 2002, 12(4): 40-45.
[4] Gao Jianke, Yang Changxiang. Prediction of deformation law of surrounding rock and backfill in deep stope in Jinchuan No.2 Mining Area [J]. Journal of Rock Mechanics and Engineering, 2003, 22(S2): 2625-2632.
[5] Fu Qiubo, Feng Lianwei, Yang Qiang. Research and application of residual mining wall mining technology in Xincheng Gold Mine [J]. Science and Technology Innovation Guide, 2015 (13): 50.
[6] North China Institute of Science and Technology. A slope displacement prediction method: China, CN103207952A[P]. 2013-07-17.
[7] Bai Jianwei, Hou Chaoyu. Research on principle and application of surrounding rock control in deep roadway [J]. Journal of China University of Mining and Technology, 2006, 35(2): 145-148.
[8] He Yongnian, Han Lijun, Shao Peng, et al. Some rock mechanics problems in the stability of deep roadways [J]. Journal of China University of Mining and Technology, 2006, 35(3): 288-295.
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Article source: "Modern Mining"; 2016.10;
Author: Yellow Sea over; Inner Mongolia Xilingol League Xianghuangqi Administration of Work Safety;
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