The stability of open pit slope is very important for the design and production of mine mining, and it has received more and more attention [1-3]. There are many calculation methods for slope stability. At present, the calculation method of limit equilibrium theory is adopted [4]. In this study, slope stability calculation software Slide Canadian Rocscience developed by limit equilibrium method to determine the slope angle of the Bayan Obo iron ore East mediator Le Gele, and stability analysis [5].
1 Project Overview
The Dongjie Leger Iron Mine is located in the Bayan Obo mining area. The open pit mining site has a length of 1100m and a width of 480m. The lowest elevation of the stope is 1384m, the highest elevation is 1648m, and the closed circle elevation is 1600m. The ore mining model is shown in Figure 1.
2 open pit slope determination
2.1 Main factors affecting the stability of mine slope
The main factors affecting the stability of mine slope are: geological conditions, hydrological conditions, earthquake and blasting vibration, ground stress and slope geometry.
2.1.1 Slope engineering geology
The iron ore in the mining area is dolomite -type magnetite and hematite, and the top and bottom plates are dominated by dolomite. Only a small amount of the ore body and the roof of the ore body are light-colored slate . The rock mass structure is dominated by blocks. The compressive strength is 55.03~105.02MPa, which is a hard semi-hard rock.
There is no large structural fracture zone in the mining area, and the fault is mostly filled with fault breccia and the geological structure is simple.
The strong weathering zone is generally developed in the mica rock, the contact fracture zone and some enamel slate. The rock is strongly weathered and is fragmented. The rock mass is fragmented and the development depth is 3~8m. The weak weathering zone has a development depth of 117 to 160.0 m, with an average of 138.5 m. The upper fissure of the belt is slightly developed, and the cracked surface has weathering marks and water rust. The lower fissure is weak, the rock is relatively intact, and the rock mass is still dominated by massive structures. .
In summary, the deposit is a block rock type mainly composed of hard semi-hard metamorphic rocks, and the engineering geological conditions of the mining area are simple types.
2.1.2 Hydrogeological conditions
The precipitation in the mining area is relatively small, mostly in the form of heavy rain. The mining area is located in the low hilly area and belongs to the groundwater recharge area.
There is no large fracture zone in the mining area. The main faults are small-scale east-west reverse faults and north-south transverse faults. They are compressive and compression-torn faults, and are mostly filled with fault breccia, which does not constitute a future open pit. The threat of water filling.
The iron ore body and its top and bottom dolomite rock mass are mainly composed of massive structures, and the Ebo layer and the flooded layer which are permeable and water-free are covered. The rock bedding and joint fissures are not developed, and the deposit is not affected much. .
The main ore body in the mining area is located above the local erosion reference surface. The topography is conducive to natural drainage. There is no surface water body and large structural fracture zone in the area. It is a simple fractured water-filled deposit with hydrogeological conditions.
2.1.3 Impact of seismic factors
Earthquakes and blasting vibrations have an impact on the slope. Through the sensitivity analysis of slope stability, it is concluded that when the slope height is less than 100m, the blasting vibration has great influence on the stability of the slope. At this time, the stability analysis should be carried out with the blasting influence coefficient; when the slope height is 100m Above, the impact of the earthquake on the entire slope is large. At this time, the stability analysis is performed by the seismic influence coefficient.
The highest level of the Dongge Leger Iron Mine slope is 239m, which is a 6-degree seismic intensity fortification zone. In the stability analysis calculation, the static equivalent effect method is used to participate in the calculation, and the horizontal earthquake is applied to the center of gravity of each block above the sliding surface. The force can be calculated as follows:
Where, Qi is the horizontal seismic force generated by the self-weight on the ith block; Cz is the comprehensive influence coefficient, taking 0.25; α is the horizontal seismic influence coefficient, and should be taken for the 7, 8 and 9 degree regions respectively. , 0.2 and 0.4, according to the National "Code for Seismic Design of Buildings" (GB50011-2010), the value is taken as 0.1; Wi is the weight of the ith block.
2.1.4 Physical and mechanical parameters of slope rock mass
A rock mass is a geological structure composed of rock and structural planes, the nature of which depends on the nature of the rock and the nature of the structural plane. Selecting appropriate rock mechanics parameters for rock mass media is an important condition to ensure reliable calculation and analysis results. Due to the lack of necessary engineering survey data, the physical and mechanical parameters of the slope rock mass are selected according to the similar works of Baiyun Obo and East Mine, and the rock mass strength is estimated based on the rock mass classification.
According to the design basic data, the occurrence characteristics of the ore body and the basic requirements of mining, the rock mechanics parameters of the selected slope are shown in Table 1.
2.2 Selection of slope angle
The design initially determined that the upper and lower plates of the open pit slope were 45°.
3 slope stability analysis
3.1Slide Software Introduction
Slide is a program for calculating the stability of soil and rock two-dimensional slopes, calculating the safety factor and possible damage of the slope, and analyzing the potential failure sliding surfaces of arcs and non-arcs. The software uses the limit equilibrium method to analyze, the calculation is simple and the results can meet the engineering needs. Considering the shape of the potential slip surface of the slope, the simplified Bishop method in the limit equilibrium method is used to simplify the Janbu method.
3.2 section selection
In order to reflect the stability state of the mine slope, according to the delineation result of the open-pit mining boundary, the section perpendicular to the slope direction and the bottom of the open-pit mining boundary is selected as the analysis section.
3.3 Analysis plan
According to the geological conditions of the slope body, in order to reflect the stability state of the slope body under load conditions, the slope profile is analyzed by self-weight + earthquake condition, self-weight + earthquake condition + rainfall.
3.4 Selection of safety factor
The determination of the allowable safety factor is the main indicator for evaluating the stability of the slope, and is often determined by the evaluation method, the engineering analogy method and the relevant design specifications. According to the national surrounding regulations, the minimum safety factor [K]=1.35 is determined according to the relevant national regulations.
If the safety factor calculated by the profile is K>[K], it is stable; when 1<K<[K], it is basically stable, and when K<1, it is unstable.
3.5 Analysis results
The results of the limit equilibrium analysis of the slope stability of the engineering geological section are shown in Table 2. The corresponding safety factor of the slope slip surface is shown in Fig. 2.
From the results of analyzing the safety factor of the slope potential slip surface of the section: the safety factor of the section is greater than the allowable safety factor of 1.35, and the slope is stable.
4 Conclusion
The calculation results are based on the similar parameters provided in the Manual of Rock Mechanics Parameters prepared by the Institute of Hydraulic and Hydropower Research. Due to the complex lithology and joint development of the Dongge Leger slope, it is difficult to accurately determine the rock mechanics parameters required for the calculation. The calculated safety factor of the slope may differ from the actual project, but the choice of the design in the design. Have a certain reference value. In the production, stress measurement, displacement monitoring and other means can be used to grasp the law of ground pressure activities in accordance with the mine, continuously improve the blasting method, reduce the water pressure and minimize the surface water flow into the open pit, to ensure the stability of the open slope.
references
[1] Zou Yuqiu. Stability analysis and parameter optimization of open pit slope in stope [J]. China Mining Engineering, 2009, 38(2): 18-22.
[2] Zhang Heng, Liu Qiushi, Liao Xingen. Open slope control and support [J]. Mining Research and Development, 2011 (4): 34-36.
[3] Ni Bin, Zhang Wei, Liu Xiaoming. Stability analysis of open pit slope based on Slide [J]. China Mining Engineering, 2013, 42(6): 28-31.
[4] Xiong Zanmin, Gao Quanchen, the application of Slide in the reliability analysis of deep foundation pit support [J]. Mining Research and Development, 2008, 28(2): 39-40.
[5] Xiao Xianguo, Lin Yiping, Yu Tao, et al. The application of Slide software in slope stability calculation [J]. Transportation Technology, 2012 (4): 50-51, 85.
Article source: "Modern Mining"; 2016.9;
Author: Xu Xu; Zhang Lin; Li Jiaquan; Sinosteel Maanshan Institute of Mining Ltd; State Key Laboratory of Mine Safety and Health metals; Hua Wei metal recycling and efficient use of mineral resources National Engineering Research Center Co., Ltd.;
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