Abstract: Generally, for some advanced open metal mines, the combined mining of open-pit and underground is adopted to extend the life of open pit mine or tide over interim of open-pit to underground, which makes the issues of the slope stability under underground mining highlighted. The slope factor of stability (FOS) solved by limit equilibrium method (LEM) is a constant value with the same geometric shape, upper load and material properties etc. of the slope, so it can not reflect the influence of underground mining on slope stability. The vector sum method which based on stress field can overcome the above shortcoming is used to solve the FOS of slip face; meanwhile, the searching of critical slip surface before and after mining is done by combined method of genetic algorithm and ant colony algorithm. Finally, an assumed example and two engineering cases are given to show the methods’ effectiveness of solving the FOS and searching the critical slip surface, as well as to indicate the variation of the open-mining slope under underground mining.

Key words: combined mining, vector sum method, genetic algorithm, ant colony algorithm