Monitoring and analysis of burning in coal tailing dumps: a case study from the Czech Republic
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The tailings are significant geological environments in mining and industrial regions. They represent special engineering-geological zones of anthropogenic sediments that require specific engineering-geological investigation. In particular, it is important to examine the sites in detail with regard to their potential heterogeneity. The article deals with an important engineering-geological issue of burning in coal mine and coal tailing dumps. A case study was implemented in a tailing dump in Hermanice located in Ostrava which is a major industrial city of the Czech Republic. In this urban agglomeration, anthropogenic sediments form 20 % of all foundation soils. Thermometric monitoring in Hermanice detected a thermally active coal tailing dump with burning as deep as 9 m. The burning is predominantly related to the content of oxygen in the body of the tailing. It belongs to the limiting conditions of the pyrophoric and consequently self-sustained burning. Other factors are sufficient contents and quality of coal mass and capacity to accumulate thermal energy of exothermal reactions. Dynamics of changes in the burning processes were identified in dependence on time, depth and distribution. There was a considerable heterogeneity of thermal activity as for all parameters, and changes were observed from the point of view of time. Considering the depth, burning gradually spread deeper. However, in the depth of 12 m, no significant thermal activity was observed within the overall studied locality. It may be stated that thermal activity is observed as much as 40 % of the studied area. Directionally, there was a progression of the process from west to east. The identified facts may be applied in final designed levels of coal tailing dumps where observational experiences identified intense cooling up to the height of 5 m preventing higher stages of self-ignition process (best situation). Tailing dumps from 5 to 12 m may already be thermally active (meeting other boundary conditions), and in tailing dumps over 12 m, it is clear that there is no thermal activity below 12 m.