Optimization of Structural Parameters of Two-step Stope in Shirengou Iron Mine

With the rapid development of the mining equipment and mining technology, high segment fill mining method in ferrous metals mining has been widely used [1].
In order to ensure the mine production capacity, improve the production efficiency of the stope, reduce the mining cost, and improve the economic benefits of the mine, most mines adopt a two-step mining sequence, that is, the first mining room, and then the mining column after filling the mine. During the mining process, the side gang is the surrounding rock of the ore body. The stability of the stope is good, the operation is safe, and the production efficiency and capacity are large. The side gang is a filling body during the mining process, and its strength is much less than that of the ore body. At the same time, the pillar is affected by concentrated stress and blasting vibration, its own strength and integrity are poor, the stability of the stope is poor, and the mining difficulty of the pillar is increased [2]. Therefore, due to the large difference between the mining environment of the mine and the pillar, the structural parameters of the mining site and the pillar should be separately analyzed to ensure the safe, economical and efficient recovery of the mine pillar.
1 engineering background
Shirengou iron ore [3-4] is a large-scale mining from open pit to underground mining, underground mining currently based. The mine is a metamorphic iron deposit for iron-silice deposits. The natural type of ore is quartzite magnetite. The ore body is 10~50m thick, the inclination angle is 65°-75°, and the average is 70°. The surrounding rock of the ore body is the black cloud angle. flash plagiogneiss, iron plagiogneiss, quartz rock and the magnet - yl dikes, of rock hard, good stability. The Shirengou iron ore mine will be converted into underground mining in three phases. The underground mining project will be in the middle of -60~-180m, with an annual output of 2 million tons of iron ore. According to the mining technical conditions of the ore body, combined with the mine's design production capacity and the problems existing in the two-step mining, the mining method is used in the mining stage after the staged rock drilling stage, and the Simba1254 trolley drills the fan-shaped medium deep hole. The bottom distance of the hole is 1.8 to 2.2 m, and the row spacing is 2 to 2.2 m.
2 two-step stope parameter optimization numerical simulation
2.1 Calculation Model Construction
Referring to the existing stope structure parameters, the area of ​​4 to 5 times excavation diameter is taken as the surrounding rock range of the stope. Therefore, the model is divided into four parts, namely the overlying load on the stope, the one-step stope body, the stope body and the stope floor (Fig. 1).

2.2 Two-step stope structure parameter simulation scheme

According to the relevant experience of using the segmented filling mining method in China, through analysis and comparison and referring to the actual situation of the current Shirengou iron ore mining, the one-step mining field selected by the stope simulation is 20m and the length is the thickness of the ore body [5]. In order to determine the reasonable structural parameters of the two-step mining site, according to the mining characteristics of the Shirengou iron ore segmental filling mining method and the stability of one-step mining, the width of the two-step mining site is 25, 30, 35m, and the length of the stope For the thickness of the ore body, the specific simulation scheme is shown in Table 1.

2.3 Rock mechanics parameters
The Shirengou iron ore body is composed of magnetite quartzite, and the surrounding rock is a hornblende gneiss. Through the rock engineering geological survey of the mining area, the rock sampling test of the upper and lower plates and the strength test of the filling body, the mechanical parameters of the rock mass and the filling body in the mining area are obtained by using the RMR rock mass engineering quality classification method combined with the Hawke-Brown formula. 2.

3 numerical simulation analysis
There are two kinds of failure modes in the top of the two-step stope [4]: ​​1 The upper part of the top plate has a large load, which causes the roof of the stope to undergo large deformation and damage; 2 the top plate tensile stress exceeds its own ultimate tensile strength after mining. Stretch damage. This study mainly analyzes the displacement and stress changes of the roof in the two-step mining process with different spans, so as to optimize the parameters of the stope.
3.1 Stress Analysis
The variation characteristics of the maximum tensile stress of the roof during the excavation of the two-step stope with different widths are shown in Fig. 2. It can be seen from Fig. 2 that as the span of the two-step stop increases, the maximum tensile stress of the top plate increases gradually, and the rate of change of the maximum tensile stress of the top plate gradually increases. When the width of the stope is changed from 25m to 30m, the maximum tensile stress of the roof of the stope is 0.165MPa/m; when the width of the stope is changed from 30m to 35m, the maximum tensile stress of the roof of the stope is 0.34MPa/m. When the span of the stope is 34-35m, the maximum tensile stress of the roof of the stope is 4.68~4.88MPa, which exceeds the ultimate tensile strength of the roof of the stope. The roof is prone to tensile damage and collapse or collapse. Threatening the safety of the stope.

The stress cloud of the roof of the stope is shown in Figure 3. It can be seen from Fig. 3 that when the width of the stope is 25m, the maximum tensile stress appears in the middle part of the roof of the stope, and its distribution area is smaller in the roof of the stope. When the span of the stope is 30m, the roof of the stope appears to be the largest. In the tensile stress zone, the distribution area accounts for 35% of the roof of the stope; when the span of the stope is 35m, the maximum tensile stress zone of the roof of the stope is very obvious, and its distribution area accounts for more than 90% of the roof of the stope, and the roof of the stope The rock will undergo tensile damage and collapse or collapse from the roof, which will seriously threaten the safety of the stope.

3.2 Displacement analysis

The displacement variation characteristics of the top plate during the excavation of the two-step stope with different widths are shown in Fig. 4. It can be seen from Fig. 4 that with the gradual increase of the width of the two-step stope, the maximum displacement of the top plate is gradually increased, and the rate of change of the displacement of the roof is gradually increased. When the width of the stope is changed from 25m to 30m, the displacement of the roof is obtained. The increase of the roof is 1.95mm/m. When the width of the stope is changed from 30m to 35m, the displacement of the roof is increased by 3.03mm/m. When the width of the stope is 33~35m, the maximum displacement of the roof of the stop is 40mm. . The actual experience of mining engineering at home and abroad can be known [6]. When the width of the stope is large and the displacement of the roof of the stope is close to or exceeds 50mm, its own stability is poor. Therefore, the two-step stope at this width The stability is relatively poor, threatening the safety of the mining workers.

The displacement map of the roof of the stope is shown in Figure 5. It can be seen from Fig. 5 that when the span of the stope is 25m, the maximum displacement in the middle of the roof of the stope is 19.8mm, and the distribution area is smaller in the roof of the stope. When the span of the stope is 30m, the roof of the stope appears obviously. The maximum displacement is 29.56mm, and its distribution area accounts for more than 90% of the roof of the stope, and the settlement is even. When the span of the stope is 35m, the maximum displacement of the roof of the stope is 44.7mm, and the width of the distribution area is 1.5 times the width of the field, the roof and surrounding rock of the stope are deformed, and the rock easily collapses or collapses from the roof, posing a threat to the safe production of the stope. A more obvious bottom drum appears at the bottom of the stope, and its displacement is small, which has little impact on production safety.

4 Conclusion
(1) The tensile stress and its change rate of the top plate of the two-step stop are gradually increasing. When the span of the two-step stop is 34-35m, the maximum tensile stress of the roof is 4.68~4.88MPa, which exceeds its limit. Tensile strength, and its distribution area accounts for more than 90% of the roof of the stope. The top plate is prone to tensile damage and the safety of the stope is poor.
(2) The displacement and the rate of change of the top plate of the two-step stop are gradually increasing. When the span of the two-step stop is 33-35m, the maximum displacement of the roof is 40mm. According to the actual experience of the project, the roof of the stope is easy to appear. Local landscaping, poor self-stability.
(3) Considering the production capacity and safety requirements of the mining stope, it is recommended that the width of the two-step stope is 30m, and the local unstable part needs to be strengthened during the mining process.
references
[1] Goodman, Li Xibing. Modern metal deposit mining science and technology [M]. Beijing: Metallurgical Industry Press, 2006.
[2] Liu Zhiyi, Hou Jinliang, Zhao Guoyan, et al. Stability analysis and engineering application of surrounding rock on the second step stop[J]. Metal Mine, 2015 (11): 143-148.
[3] Zhang Jianyong, Su Jianjun. Selection of mining methods for the third phase of Shirengou Iron Mine [J]. Metal Mine, 2013 (1): 23-26.
[4] Zhang Haibo, Song Weidong. Study on the mechanism of filling backfill and surrounding rock after filling in open field [J]. Chemical Minerals and Processing, 2014(1): 41-44.
[5] Wen Zhanguo, Zhang Congjun, Ji Zhicai. Discussion on the third stage mining method of Shirengou Iron Mine [J]. Modern Mining, 2014(9): 30-33.
[6] Liu Zhiyi, Zhang Lichun, Zhao Guoyan, et al. Structural parameter optimization and engineering application of two-step stope based on FLAC3D [J]. Metal Mine, 2015(10): 6-10.
Author: Xu Chang Xin; Hebei Iron and Steel Group Mining Company Shirengou iron ore;
Article source: "Modern Mining"; 2016.7;
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