Rock engineering method to pre-evaluate old, small coal pillars for secondary mining

摘要

Due to the approaching depletion of reserves in the Wilbank Coalfield, and the fact that the Waterberg Coalfield is as yel underdeveloped, there is increasing pressure to extend the lives of the operating coal mines in the Wilbank Coalfield. One potential source of coal is the old pillars, often small and at shallow depth, that were not left with secondary extraction in mind. At face value, some of these pillars appear to be suitable for secondary mining due to their high safety factors. However, it is known that over lime, these pillars have scaled and the current sizes are smaller than the as mined dimensions. It is also known that at shallow depth, the overburden is often less likely lo fail during secondary mining, resulting in high abutment loads on the unmincd pillars.