Abstract

Optimal stope dimensions for underground mining using the Sublevel Stoping method are selected to guarantee excavation stability. The stability graph method developed by Mathews et al. (1980) is used as an empirical tool for this purpose. The stability graph relates the stope walls’ hydraulic radius with the stability number N defined by N=AxBxCxQ′, where A, B and C are adjustment factors for stress to strength ratio, joint orientation and gravity effect over stope walls, respectively, and Q′ is the modified rock tunneling quality index (Barton, et al. 1974). In the stability method, the water condition is not considered since the registered cases presented dry conditions. The objective is to include the water condition in the stability graph method. This is accomplished by using the joint water reduction factor (Jw) and the inflow of water observed in the drifts. Therefore, the stability number with water conditions is defined by N=AxBxCxQ′xJw. A database of 25 case histories is collected and analyzed for a mine with the presence of underground water with software MineRoc®. Stability boundaries are proposed based on the Equivalent Linear Overbreak/Slough (ELOS). The impact of the water reduction factor is analyzed, and an overall improvement in the definition of the stability boundaries is observed.