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Results

 

 

Test site 2. Witbank - Coal Fires

 

The Blesboklaagte area to the east of the Ferrobank industrial area has been undermined as is evidenced by the collapsed bord and pillar structures and the coal discard dumps. The D&O mines database indicates the abandoned mine is the now defunct Blesboklaagte colliery. After the original bord and pillar mine operations were abandoned and the roof of the shallow mine collapsed subsidence formed over a large area. These subsidence features can be observed in the residential area as well as unused areas south of the airfield and north of the informal settlement (Figure1). These areas are considered unsafe and some markers along the tar road serve as warning signs. However, residents from the small informal settlement are crossing the area on a daily basis. Damage to infrastructure has been noted in the form of a high voltage electricity pylon which is in the process of collapsing.

Figure 1: Collapsed features in an informal settlement
Figure 1: Collapsed features in an informal settlement

During the field campaign several coal fire sites were visited and thermal signatures and imaging collected. These sites were spread over areas where abandoned underground coal mines have collapsed, rendering the area unsafe for human activities. Collieries in the Witbank coalfield have historically used board and pillar mining with typically low coal recovery ratios, leaving a significant amount of coal in pillars, and as floor and roof coal. When old workings were reopened, ingress of air into galleries resulted in chemisorption and oxidation of coal leading to spontaneous combustion in some collieries. Shallow mining (<100 m) leads to severe disturbance of the surface, including cracks and obvious subsidence. One of the consequences of coal mining is the exposure of the coal to air and moisture resulting in the ignition of the coal through the processes of chemisorption, oxidation, and spontaneous combustion. In this area the collapsed mine features resulted in the influx of water and air which exacerbated the propagation of spontaneous combustion. The collapsed features observed in this area include cracks and large open holes which are either steaming or burning (Figure 2 and Figure 3). Many burning underground coal fires have been observed in the area.

Figure 2: Burning collapsed coal mining area
Figure 2: Burning collapsed coal mining area

 

Thermal image Sinkhole coal fire image
Figure 3: Thermal (left) and visible (right) images of a mine-related sinkhole showing elevated temperatures due to underground fires