Application of FLAC Software in Stability Analysis of an Open Pit Slope

1 Overview of the mining area

The formation of an open-pit mine is complex, and its composition includes the pre-Sinian and subsequent sedimentary layers of deep metamorphic and mixed rock. Hornblende biotite gneiss plagioclase folder is the main magnet quartzite lithology. Due to the obvious granitization effect, some metamorphic rocks still have residual, and there are lentils in mixed rock and mixed granite. The Shahe River and the Weihe River are important surface water systems in the mining area, while the Bangmushan Iron Mine is only 2km away from the Weihe River and about 500m away from the Shahe River. There is moderately rich water and weakly confined pore water in the Quaternary strata in the southern part of the ore body. The Quaternary stratum is 14~30m thick, the elevation is 59.5~40.6m, and the groundwater depth is 9.5~14.5m. 55.1 ~ 65.5m. There is a large fault in the southern slope of the mining area, running N50°~60°E, inclination angle 70°, and the fault lacks vein rock. The north and south slopes of the open pit mine are cut by faults, and there is a problem of water seepage in the southern fault, which seriously threatens the stability of the slope of the open pit mine. At present, the mining elevation is -76m and the maximum slope height is nearly 200m.
2 stability analysis
2.1 Calculation parameters
According to the engineering geological conditions, the southern slope of the mine is cut by large faults. The slope has more water outlets and a larger amount of water, which is a major factor affecting the stability of the slope, especially in the rainy season. The impact is even more serious. Therefore, this study intercepts the stability analysis of the southern slope section of the open pit of the mine. The elevation of the section is 66m, the elevation of the slope is -124m, the height difference is 190m, and the total slope angle is 38°. Through the indoor rock mechanics test, according to the geological exploration data and the drilling sampling analysis, the strength reduction coefficient method [1-4] is used to obtain the rock mass mechanical parameters of each layer of the slope (Table 1).

2.2 Stability analysis results

It is calculated that a safety factor of 1 maintains the ultimate balance of the open pit slope. The results of the stability analysis of the open pit slope are shown in Figures 1 to 5. It can be seen from Fig. 1 that the elevation is 42-66 m, the stress is concentrated and the strain is extremely large, which causes the slope to be in a dangerous environment. It can be seen from FIG. 2 to FIG. 4 that some units of the Quaternary soil layer are located above the envelope of the Quaternary soil layer and the rock layer. It can be seen from Fig. 5 that the plastic zone of the whole section is basically in the range of 42-66 m, and the squall layer in the Quaternary soil layer and a small part of the weathering layer in this range is in an unstable state.

In order to confirm the unstable area of ​​the slope, the displacement vector diagram and the displacement velocity vector of the slope grid unit are drawn by FLAC software, as shown in Figure 6 and Figure 7, respectively. It can be seen from Fig. 6 and Fig. 7 that the unit displacement vector of the quaternary soil layer and the partially weathered layer (elevation 42 to 46 m) is the largest.

3 Conclusion

Taking an open pit mine as an example, the numerical model of the mine slope was established by FLAC software, and the slope stability analysis was carried out. The safety factor of the slope in the limit equilibrium state was 1. Through the analysis of the failure envelope diagram of each layer, it can be seen that the Quaternary soil layer and a small part of the weathering layer are in an unstable state. In this gang, the drainage and dewatering and slope unloading methods can be used to improve the Quaternary soil layer of the slope. And the stability of a small part of the weathering layer ensures the safe operation of the mine open pit mining work.
references
[1] Liu Bo, Han Yanhui. FLAC example analysis tutorial [M]. Beijing: China Communications Press, 2005.
[2] Liu Bo, Han Yanhui. FLAC principle example and application guide [M]. Beijing: China Communications Press, 2005.
[3] Chen Sha, Yue Zhongqi, Tan Guohuan. Numerical analysis method of heterogeneous geotechnical engineering materials based on digital image [J]. Chinese Journal of Geotechnical Engineering, 2005, 27(8): 956-964.
[4] Liu Baozhen. Introduction to mine rock mechanics [M]. Hunan: Hunan Science and Technology Press, 1982