With the increase of the slope height in open-pit mines, the contradiction between the mining safety and stripping quantity becomes progressively serious. According to the analysis and calculation, the original slope angle in Gaocun Iron mine is conservative. After engineering geological investigation and rock mechanical tests, three optimization schemes were proposed. FLAC3D numerical simulation software was used to analyze the slope stability by several indexes such as displacement and plastic zone. In addition, the safety factors were obtained according to the limit equilibrium method by Geo-slope software. Eventually, the final slope angle of the mine was determined. It showed that the optimized slope angle is improved by 3° compared with that of the former design on the whole, and the slope stability well meets the requirement of production.
There are a growing number of metal mines carrying on deep mining in our country, and the design of open pit slopes faces a dilemma in that situation: When the slope angle is too big, the steep slope will cause instability and failure, which is not conducive to the normal production of the mine; In contrast, the small angle will increase the stripped amount and the production costs significantly. To solve this problem, slope angle must be optimized on the premise of mining safety (Heok & Bray 1981, Duncan & Christopher 2005).
Gaocun pit of Nanshan Mining Co., Ltd., is a large open pit mine, whose ore production has reached 7 million tons per year with the total mining and stripping of 18 million tons. After entering the second phase of open pit mining, the north-south length of the stope expands from 780 m to 1500 m, and the east-west width expends from 575 m to 820 m. The highest level of open pit mining is up to +90 m and the bottom elevation is down to-186m. Under the conditions of high and steep slope mining, with mining depth increases, the contradiction between security and economic production is gradually highlighted. Therefore, slope design must be optimized to ensure the production safety and increase economic efficiency.