Coal Mines are coal mines are coal mines...but not always

Following an early start, we head east from Pretoria to the Witbank area for my first visit to a South African coal mine. Joining me today is Dennis and Leon, Mine Surveying Inspectors from the Department of Minerals and Energy (DME). Douglas is a bord and pillar mine in the throws of winding down and will cease production toward the end of the year. The Inspectors' task today is to conduct a routine audit on selected roadway underground (typically under highways or other critical imfrastructure), ensuring that they meet design criteria and are correctly plotted on the mine plan along with a general audit of plans. One of the critical areas is the width to height ratio and the intersection dimensions. Douglas carries out first workings in multiple seams where the pillars are overlain with roadways typically in the order of 6.5m wide, Pillar factor of safety is an important consideration.

The inspection involved a conventional chainage and offset ribline survey with additional measurements taken for intersection diagonals and extraction widths. Back in the office this information is plotted along with the calculation of factor of safety and width-height ratio. Provided that these numbers are within tollerance then the inspectors are satisfied. Examination of plans typically highlights areas where the plan does not conform to the standard or reveals an omission.