Secondary Water Saturation of a Carboniferous Rock Mass in a Liquidated Mine as the Cause Behind the Changes in Geomechanical Conditions and State of Hazards in Active Mines of the Upper Silesian Coal Basin
Bukowski, Przemysław (1); Rapantova, Nada (2); Bukowska, Mirosława (1); Hemza, Petr (3); Niedbalska, Katarzyna (1)
1: Central Mining Institude, Poland; 2: Technical University of Ostrava, Czech Republic; 3: Green Gas DPB, Czech Republic
The abandondment and flooding of underground mines is a process that significantly changes the hydrogeological and geomechanical conditions within the mine and in its environment. Water saturation of the rocks surrounding the flooded workings is the main reason behind their weakening, and subsequently behind the geomechanical processes leading to the occurrence of roof caving and clogging of the water flow as well as the decrease in the durability of safety measures, e.g. safety pillars. The results of the geomechanical processes induced by changes in hydrodynamic conditions progressively escalate further changes in the conditions and directions of water and gas flows in the decommissioned mine.
The possible interactions of hydrogeological and geomechanical conditions in a liquidated mine are examined on the basis of the results of cohesive rock studies of various lithostratigraphic series, conducted for various degrees of rock water saturation. Such a water hazard assessment was performed on the example of an active mine where mining activities were conducted adjacent to a mine water reservoir. The hazard level analysis was conducted based on the evaluation of the scope of influence of the rock geomechanical property changes, occurring as a result of gob flooding and the renewed water saturation of the rock mass, on the condition of the safety measure – a safety pillar.
The main objective of the article was to justify and prove the necessity of conducting hydrogeological condition and natural hazard analysis in decommissioned mines together with the assessment of changes to geomechanical conditions. That is because there is a strict correlation between hydrogeological and geomechanical conditions with regard to the evaluation of mining hazards, particularly water, roof caving, rock burst, fire and gas hazards.
The article presents some applications of the interdisciplinary analysis of the hydrogeological and geomechanical consequences of underground hard coal mine working decommissioning and flooding. It recommends the implementation of procedures determining the most dangerous conditions possible resulting from the changes to the water saturation of the rock mass during mining hazard assessment. As an example, it suggests this implementation during the assessment of the safety conditions of projected mining activities and the verification of safety measures, e.g. during the determination of safety pillars and zones, and also during the forecasting of water hazards under the conditions of the necessary protection of active mines and the clogging of waters.