Mining through areas affected by abnormal stress conditions at Syferfontein Colliery

摘要

This paper investigates the conditions leading to the indefinite terminationof production in four critical primary panels at an underground coal miningoperation, the observed shortcomings in the mining approach, and theproposed strategy to mine through the affected panels. Initial assessmentof the abandoned panel conditions indicated time-dependent strata failure,(i.e. bolted roof failure overrunning intersections), which occurred frommere minutes to up to four weeks post-production, with and without priorwarning of failure. This prompted the constant re-supporting of back areas,which raised safety and productivity concerns. Investigation of the initialmining conditions revealed that the failures were due to a criticalcombination of factors, the chief of which was isolated horizontal stress.Other factors that were initially overlooked by the mine (i.e. influence ofhydraulic stress, misinterpretation of borehole data), resulted in theconditions being described as abnormal. Remedial actions were determined,and in so doing, a new strategic approach was formulated to thoroughlyaddress all failure concerns. The four panels were explicitly planned toserve as the main intake and return airways for the recently commissionedsecondary ventilation shaft, as well as providing access to millions of tonsin proven coal reserves. It is thus imperative to mine the panels. Afeasibility study showed that the proposed strategy set for implementationwould be financially viable.