Review of Roof Skin Instability Challenges with Emphasis on South African Coal Mines

Abstract

AbstractSouth African underground coal mines continue to be challenged by roof skin instability problems. Falls of ground between installed bolts, roof skin delamination and dislodging of weathered roof skin material between the bolts are characteristic of ‘friable’ roof. Roof skin can be described as roof surface material not extending to more than 10 to 15 cm into the roof. Typical incidents associated with roof-skin falls are body scratches, limb amputation and even fatal occurrences. South African underground coal miners’ perceptions of roof-skin instability and approaches to deal with it, are rather informal and somewhat not standardised.For most of South African underground coal mines, installation of Osro straps is usually the first step in mitigating against roof skin problems. Osro straps provide partial areal roof coverage. Two main products are known to be used in South African underground coal mines, plastic nets and welded wire mesh. These products are used sparingly at highly prioritised areas where roof-skin problems cannot be overlooked. However, one underground mine in the Vaal basin is known to have adopted total areal coverage (welded-mesh) approach as a result of serious friable roof problems. One other mine is known to be currently in the process of rehabilitating belt roads and travelling ways for hundreds of kilometres using plastic nets. The use of surface liner products is very rare. At the moment only one mine in the Secunda area is known to be using fibre-reinforced cement based liner called Tekcrete Fast M at selected high risk areas in the belt road. The author visited that mine and observed that the product adheres very well to the coal roof surface. The product however is also known to be very expensive and not intended for large scale use but for select high risk zones. Most prominent approach for majority of the underground coal mines in South Africa is physical roof barring. Several changes have been made to pinch bar to encourage effective barring. Some South African mines are known to train and issue every employee deployed underground with ‘barring certificate’. Whether there are any significant physical barring limitations is another separate issue yet to be dealt with.In general, responses to several issues and questions pertaining to roof-skin instability in South African coal mines are unclear and need investigation in order to enable the industry to wage a collective and harmonious combat against roof skin problems. Some pertinent issues and questions are: Justification and clear recognition of roof skin problems in South African coal mines. Are South African coal mines mitigating well against roof skin problems, and what are these mitigating efforts? Past or current paper pertaining to roof skin problems in South African underground coal mines. What are the perceived and encountered challenges in addressing this problem? Are there positive notable trends, forecasts, developments or milestones in regards to dealing with roof skin problems in South African coal mines? This paper will attempt to investigate these issues, outline their status and exploit the opportunity to standardise the approach to deal with roof skin instability.