Sijiaying Iron Mine Stope West Side Slope Treatment Scheme

Currently, szechiaying iron ore has entered a phase of deep mining, due to the complex geological conditions, mine engineering, combined with frequent production mine blasting vibration, resulting in many rock edge to help rifting occurs, slumping, West Slope stope there Partial slump. The existence of the sliding body makes the lower steps unable to be bounded by the design, which hinders the normal operation of the mine production, seriously affects the production capacity of the mine and restricts the continuous and stable production of the mine. In order to ensure the normal production of mines and the safety of personnel equipment, it is necessary to analyze the stability of the slope and propose corresponding treatment plans for the sections with unstable deformation or potential deformation according to the analysis results.
1 Research area overview
The thickness of the Quaternary soil layer of the west slope of Sijiaying Iron Mine is 51~68m, mainly composed of silt, silt, cohesive soil and strong weathered quartz sandstone , shale, etc. The aquifer is rich in water and has a large change in the slope angle. Under the condition of water seepage erosion, the soil layer is prone to instability and damage [1]. The investigation of the west slope was carried out, and the stable water level of the drilling hole was 31.00~34.00m, and the water level elevation was -12.75~-9.62m. The groundwater recharge source in this area was mainly atmospheric precipitation and lateral runoff recharge. .
1.1 Landslide overview and instability mechanism
On October 8, 2013, the slope of the special thick alluvial slope of the N#14～N16# line of the first phase of the Sijiaying Iron Mine was landslide, and the landslide was the Quaternary sub-sand (soil), the height of the landslide. About 55m, from the surface elevation of 38 ~ -18m level, length 100m, cut horizontally along the soil floor, sliding distance of 60m, the calculation model of the N15# line slope landslide and the status of the slope after the landslide is shown in Figure 1. The landslide at this location indicates that the thickness of the Quaternary sub-sand reaches 55m, the slope angle is 33° (35° according to the designed soil step slope angle, and the overall slope angle is 33°), and the soil floor is eroded by water seepage. Underneath, an approximate arc-shaped instability failure occurs [2].

1.2 landslide inversion results
The Geo-Slope software was used to analyze the slope landslide (set the stability coefficient to 1.0), and the calculation was carried out according to the arc sliding method to obtain the mechanical parameters of the slope soil [3]. The inversion slope failure mode is shown in Fig. 2. The calculated parameters of the slope landslide inversion are calculated. The subsoil capacity is 20.9kN/m3, the cohesion is 9.5kPa, and the friction angle is 18°. According to the mechanical test results of the Quaternary silt layer of Shandong Institute, the cohesive force of the layer is 20 kPa, the friction angle is 20°, and the erosion of the groundwater is weakened by long-term, when the cohesion is 9.9 kPa and the friction angle is 18°. Instability and destruction [4-7].

1.3 The necessity of landslide control
In the strip-like range of the N6#～N16# line of the Sijiaying iron ore mining, the geometrical conditions of the topsoil and underlying strata of the slope are the same, and the slope also has the possibility of instability and damage. The instability is due to the fact that the thickness of the sub-soil layer is gradually thinner from the north to the south, that is, from the N16# line to the N6# line, and the gravel and clay layers are mixed. The N12# line profile and the thickness of the alluvium layer are shown in Figures 3 and 4, respectively.

The N15# line landslide inversion analysis index was used to evaluate the stability of the N12# line slope. Although the N12# line soil thickness (40m) is smaller than the N15# line, the soil layer slope angle is steeper (40°). According to the analysis, before the treatment, the stability coefficient of the N12# line slope can not meet the reserve requirement of 1.2, and must be cleaned. Otherwise, in the rainy season of the coming year, a landslide disaster similar to N#15 line may occur, which seriously affects the mine. Production, endangering the safety of multiple high-voltage towers and belt corridors on the ground. The stability calculation results after the weight reduction of the upper part of the N12# section shows that after 20m from the ground to the west, a step of 12m high is formed in the broken section, and the slope stability coefficient of the whole soil layer will increase to about 1.19. .
2 stope west gang N10#～N14# section landslide treatment plan
2.1 Scheme 1 (slope cutting project)

Figure 4 shows that the thickness of the sub-soil layer from the north to the south (N16#～N6# line) is gradually thinner, and the thickness of the soil layer is gradually less than 30m in the south of the N10# line, and the stability of the slope is improved. According to the N10#, N11#, N12#, N13#, N#14 line profile (Fig. 5 to Fig. 9), the N10#～N14# section slope is sloped, and when the ground is facing west, it is 20m. After that, the broken section forms a step of 12m high. After calculation, the amount of earth to be cleaned is about 11.1.
Million m3, the statistical results of the earthwork of each section are shown in Table 1.

Since the west ground frame is provided with a ring-shaped power supply line and a high-voltage line tower, the poles of the nine ring-shaped power supply lines will be located inside the new shoulder position after the expansion, and need to be moved. At the same time, after the expansion, there will be three high-voltage towers close to the new shoulder. The shortest distance between the high-voltage tower numbered GY20-23 and the extended shoulder is only 2m. To ensure the safety of the tower, it should be moved. . However, in view of the fact that the movement of a single tower is not only costly, but also affects the balance and stability of the adjacent towers, it will also cause the power supply of the second phase of the plant to be interrupted. Therefore, according to the site survey and economic accounting results, reinforcement measures have been taken. To avoid moving the tower; the two high-voltage towers numbered GY16-18 and GY34-36 are 13~20m away from the shoulder, and local key reinforcement measures are also needed. The statistical results of the nine utility poles that need to be moved and the three high-voltage towers that need to be reinforced are shown in Table 2 and Table 3.

2.2 Scheme 2 (slope nail nail reinforcement)
In order to prevent landslides, soil nails can be reinforced at the foot of the slope at the lower part of the step, and the bedrock can be driven to improve the stability of the slope. Mechanism of soil nailing: 1 The effect of the hoop skeleton, which is determined by the stiffness and strength of the soil nail and its spatial combination in the soil. It has the effect of restraining the deformation of the soil and makes the composite soil a whole. 2 share the role, in the composite soil, the soil nail and the soil jointly bear the external load and the soil weight stress, the soil nail plays a role of sharing, the proportion of soil nail sharing depends on the relative stiffness ratio of soil nail to soil, soil The spatial position of the nail and the stress level of the composite soil; 3 stress transmission and diffusion, under the same load, the strain level of the soil part of the soil nailing wall is lower than that of the plain soil slope, thus delaying the formation of the cracking domain And development [8]. The soil nail construction position is shown in Figure 10 to Figure 14. The new drilling position and depth are shown in Table 4.

In the second scheme, there are 5 soil nails in each section, including 2 slopes on the upper slope of the slope, 3 platforms, 2m adjacent to each other, 1 row of soil nails separated by 2m, and 1005 soil nails for 400m width. The nail length is 30m, and a total of 30150m soil nails are required.
In Scheme 1, because the high-voltage towers on the ground cannot be moved, only the slopes and reinforcement schemes of the slopes can be adopted. Since the slowing of the slopes will affect the final boundary position of the pits, the feasibility of the second scheme is better than that of the first scheme. high. From the perspective of the stability of the west slope, as the supporting and pre-project of the soil nail reinforcement scheme, the necessary protective measures still need to be taken include: 1 slope protection project to prevent the slope surface from being washed by rainfall; 2 the foundation rock roof needs to be constructed horizontal drain hole Engineering, dredging groundwater; 3 slope monitoring project; 4 surface anti-seepage project, in addition, the soil slope as soon as possible according to the design boundary to help the boundary.
3 Conclusion
(1) Determine the landslide mechanism of the sub-soil layer of N15# line, that is, under the condition of water seepage erosion in the soil floor, the horizontal cutting along the floor of the soil layer will occur, and the arc-shaped instability failure will be approximated. It is 20m, the horizontal distance of the slope is 60m, the height of the landslide is about 55m, and the elevation of the surface is 38~-18m, and the length is 100m.
(2) Through the back analysis of the strength of the landslide in the sub-soil layer, the cohesive force of the soil layer is determined to be 9.9 kPa, and the friction angle is 18°. According to this, the treatment position of the west slope of the Sijiaying iron mine stop is N10#～ N14# section.
(3) Considering the high-pressure poles existing on the ground, in order not to affect the final boundary position of the bottom of the pit, it is determined that the slope-rock treatment is carried out by using the soil nail construction stable slope rock mass scheme, and the scheme is to hit the soil at the slope and platform of the lower slope of the soil slope. Nail, deep into the bedrock, thus improving the stability of the slope rock mass, can maximize the stability of the current slope, and avoid the transfer of high-voltage towers and utility poles. In addition, when the scheme is implemented, it is necessary to level the water hole in the soil rock contact zone to drain the groundwater. In addition, it should also ensure that the soil slope is supported by the design boundary as soon as possible.
references
[1] Lu Quncai. Stability analysis and treatment technology of soil slope [D]. Nanjing: Nanjing University, 2014.
[2] Song Aidong, Guo Xianzhang, Gao Ruiyong. Study on the causes and treatment measures of slope slope of Sijiaying open pit mine [J]. Metal mines, 2012 (12): 24-27.
[3] Deng Literature, Yang Tianhong, Nan Shiqing, et al. Determination of rock mechanics parameters and stability analysis of the east slope of Sijiaying Iron Mine [J]. Metal Mine, 2016 (3): 15-19.
[4] Jin Aibing, Sun Jinhai, Wu Shunchuan. Study on stability analysis and treatment plan of deep mining slope in open pit mine [J]. Metal Mine, 2005 (6): 5-8.
[5] Jia Suiping, Zheng Luzhen, Zheng Lulin. Stability analysis and treatment plan for large-scale landslides on open slopes [J]. Metal Mine, 2014 (5): 27-31.
[6] Shen Guoqiang. Study on stability analysis and treatment plan of high slope under complex geological conditions [D]. Xi'an: Xi'an University of Architecture and Technology, 2014.
[7] Wang Nan. Numerical analysis of seepage and mechanical properties of the eastern slope of Yanshan Iron Mine [D]. Shenyang: Northeastern University, 2014.
[8] Xie Quanmin, Ding Baoyan, Wu Dinghong, et al. Case-based slope management plan selection decision support system research [J]. Rock and Soil Mechanics, 2008 (5): 1351-1354.
Author: Yang Wei; Institute of Mining Engineering, North China University of Technology; Luan County in Hebei Iron and Steel Group Co., Ltd. Sijiaying iron ore;  
Zhang Yunpeng ; School of Mining Engineering , North China University of Technology;
Article source: "Modern Mining"; 2016.6;
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