| Open pit mining is used for90%of iron ore and46%of non-ferrous metal mines in China. Open pit mining has played an increasingly important role in China’s mining production. With the development of technology and equipment of open pit mining, the number and scale of mines are increasing. The artificial slope is increasingly high after mining method being transformed surface mining into deep open pit mining. At the same time, the risk of destruction and damage scale of slope will be increasingly。Therefore, the stability of slope has become one of the important issues in open pit mine. It is necessary to adopt a scientific approach for evaluating the design scheme of slope to ensure safe and efficient production in mine.For the average large deep open pit mines, the stripping amount can reduce range from3.43%to3.91%when the slope angle steep increase1°in the range of30°～60°. But the large slope Angle may bring instability problems which results in phenomenon such as deformation or destruction of slope and threatens the personnel and equipment safety in open-pit mining. Therefore, it is necessary to optimize the design parameters based on stability analysis of slope. Contradictions between slope stability and decrease the stripping amount must be reasonable solved, to create economic benefits for the mine and ensure safe and efficient production simultaneously.Qinghai Songshunangou gold mine is a typical magmatic deposit, and the bedrock is integrity. This mine is suitable for large scale open pit mining, because the orebody is located in the mountain, in addition, the engineering geological and hydrologic condition is simple. The stability of mining slope is evaluated comprehensively and systematically by using evaluation system containing different research methods based on the existing prospecting and field investigation data. The main influence factors of soil slope, rock steps slope and whole slope in mine are analyzed. On the basis of the stability analysis of slope, the design parameters are pointedly optimized, and the systematically optimization research of mine slope is realized finally. The main content of this article and research conclusions are as follows:(1) By analyzing the existing prospecting and field investigation data, the geological structure, engineering geological and hydrologic condition, mine design parameters, damage in the Songshunangou mine are obtained. The main influence factors of slope stability are summarized, and the main damage types of mining slope are studied. The calculation model is made by the existing prospecting data and the parameters are acquired by laboratory test to analyze the stability and optimize mining slope. The mine is located in north Qilian Caledonian fold belt and near the southern edge of deep fracture of Dabanshan. The southern of fracture is central uplift belt of Qilian Mountain in the Precambrian. The basic seismic intensity is VH degrees. There is a large fault in the southwest slope. The dip of fault is contrary to slope aspect, which has a great impact on stability of slope. It is necessary to focused research the fault. The geography is south higher than north. The highest elevation is3900m and generally between3450m and3800m. The relative elevation is200-400m generally. The impact of heavy rain needn’t be considered on slope stability in mine because the effect of rainfall is minimal to mine slope stability. The main damage is local failure of steps slope, and the main controlling factor is all types of small structures surface. There are three damage types in the mine mainly, which are plane sliding, wedge destruction and toppling. The wedge destruction is the main damage types in Songshunangou mine.(2) The main influence factors of slope stability are summarized, and the main damage types of mining slope are studied. The analytical methods which suit the high and steep slope in Songshunangou mine are selected to establish the stability evaluation system by compare and choose slope stability analysis methods. All types of slopes in the mine are analyzed by using different method or software. The stability factor of soil slope is calculated by using limit equilibrium theory. The local failure of steps slope is analyzed by using the stereographic projection method. The three-dimensional model is built by using the ANSYS software. The distribution of stress and strain field in the mine is calculated on the condition of natural conditions and earthquake by using FLAC software. The stability factor of whole slope is calculated by using strength reduction method.(3) The stability of slopes is evaluated by using different methods in the mine.①The distribution area of soil slope is very small, and mainly distributed in the highest steps slope of mine. The stability factor of soil slope is less than safety factor on the condition of natural conditions and earthquake by using slide software. It is necessary to further optimize the slope design parameters.②The whole slope have a stable state on the condition of natural conditions and earthquake, and a large volume of excavation does not result in overall slope damage by analyzing the calculation result of mine three-dimensional model.③The excavation has the same degree of influence to the maximum and minimum principal stresses of toes, and has larger influence to the value of the maximum principal stress. Compared with the state of nature, the change of displacement amplitude is largest, then the maximum principal stress is larger, and the change of minimum principal stress is large in the condition of earthquake.④The stability factor of typical section is of whole slope is calculated by using strength reduction method. The stability factor of whole slope is1.95under the natural state and1.6under earthquake, and the stability factor of whole slope is2.05without considering the fault. The stability of whole slope meets the requirements.⑤The local deformation and failure of rock steps slope in mine is inescapable. The I area is not only the maximum height slope, but also the richest failure type in all geological zoning. According to the characteristics which the mine slope allow small scale damage of mining slopes, the degree of slope partial destruction can be reduced to ensure the safe and efficient mining by optimizing the design parameters of steps slope based on less impact to the design parameters of whole slope.(4) The influence of slope stability coming from design parameters is analyzed. Different design parameters is optimized by specific different optimization methods and the design parameters of whole slope is optimized finally. The design parameters of whole slope contain height, angle, platform width and combinations of steps slope. These four parameters determine the form and slope angle of whole slope in mine. For the same slope angle of steps slope group, the stripping amount can be decreased when increasing the width of clean platform or reducing the width of security platform. Based on the stability analysis of slope in mine, the angle of soil slope is optimized by using limit equilibrium theory. The angle of steps slope is optimized by using the improved qualitative analysis method of wedge. The33prioritization scheme is calculated by using the numerical simulation. Finally, the optimization parameters of slope are obtained in the Songshunangou mine. The optimum angle of soil slope is intended to be43°after optimizing analysis in the condition of earthquake and checking computations in the state of nature. After computing and analysis, the optimum parameters of rock slope (beside TTT area) is obtained:the width of clean platform is12m, and the width of security platform is3m, and the angle of steps slope is65°when the height of steps slope is more than3830m; the width of clean platform is10m, and the width of security platform is3m,and the angle of steps slope is70°when the height of steps slope is less than3830m. The optimization solution of mining slope can decrease the stripping amount effectively.The design parameters of mining slope has a extreme close relationship on creating economic benefits for the mine and ensuring safe and efficient production simultaneously. It is very necessary to establish a stability evaluation system to systematic evaluation the slope stability, and optimize the design parameters of slope in mine. The research in Qinghai Songshunangou mine can provide powerful basis for creating economic benefits and ensuring safe and efficient production. At the same time, the research can provide a reference for the design of mine whose engineering geological condition is similar to Songshunangou mine. |
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