Use of B Factor from Major Geological Faults' Orientation on Mathews' Stability Graph Method. a Case Study.

Optimal stope dimensions for underground mining using sublevel stopping method are decided ensuring excavation stability. Stability graph method developed by Mathews, et al. (1980), later modified by different authors is used as an analytical tool to achieve this purpose. Mathews' B factor represents the influence of minor rock mass discontinuities (joints) on the over break volume of stope's walls. However, in a highly fractured rock mass, it is very likely to have at least one joint set orientated sub parallel to every stope's wall, thus accounting for a low value for B factor. This will have a significant impact on stability number's value while not necessarily reflecting the stopes failure mechanism on large stopes as joint's dimensions are small compared to the stope's. Major geological faults, on the other hand, are of bigger dimensions, thus their influence on a stopes overbreak volume is important. This paper presents a comparison between two stability graphs, one created using Mathews' original method and another created using B factor as a mean to measure the influence of major geological faults in the over break volume of stope's walls. Both graphs were made using information from the back analysis of the same stopes and using the software c.