Bezpieczeństwo Pracy i Ochrona Środowiska w Górnictwie Number 07/2018

Polish coal mining is characterized by the presence of virtually all natural hazards that typically occur in underground exploitation, and especially of threats of disasters.

Disclosure of these threats can cause dangerous events, often resulting in accidents, including fatal accidents. The high level of natural hazards may furthermore put heavy constraints on mining activities or can even lead to exclude disaster-prone areas from exploitation. Decommissioning certain parts of deposits may lastly reduce the production capacity of mines, and in some cases may even shorten their life span.

The paper reviews the geological and mining conditions and scale of natural hazards occurrence in the coal mining sector. On the basis of the statistics concerning dangerous events and fatalities caused by natural hazards in the years 2000-2017, the following conclusions were presented: (i) In terms of the number of dangerous events, the most common were endogenous fires, rock bursts as well as ignitions and methane explosions, and the least frequent included coal dust explosion, methane and rocks outbursts and water inflow. (ii) The majority of fatal accidents occurred as a result of methane or coal dust explosions, while significant number were caused by rock bursts. Water-related accidents, endogenous fires as well as methane and rocks outbursts caused the least fatalities. (iii) The methane and coal dust explosion are the most catastrophic, although the incidence of these threats has been low. (iv) The analysis of hazardous incidents and fatal accidents caused by these threats confirms their significant impact on work safety in coal mining.

Two mine walls were used in a selected hard coal mine in strong rock burst conditions, in the direct vicinity of fracture zones or deposit residue.  To ensure the safety of the crew and to protect the pits against damage, before opening any longwall fronts, active anti-burst prevention was applied in the form of focused hydraulic fracturing or tensional-relief shooting. An increased-strength ŁP10 and ŁP12 HŁ CORR casing made of S480W steel was applied in longwall pits. Its large cross-section increased the mining capacity of the walls and limited the climate- and methane-induced threats in their areas. To preserve the stability and supporting strength of the pit casings, they were reinforced at the stage of drilling, and a part of the longwall pits were completely excluded from human traffic, only enabling control of their state or emergency transport after an eight-hour pause in extraction and positive assessment of the mine geophysics station. These measures contributed to a success in the form of planned wall mining.

In open-pit mining, landslides are some of the most severe threats to the operation of mining facilities and general safety.  The article presents a landslide which occurred in May 2017 in the “Zastawie IV-2” open-pit mine extracting natural aggregate from under the water surface using a dredger. The main natural factors facilitating their formation are: variability of geological structure (compacted formations on top, loose formations below the water surface), inclination of land and rock layers towards the pit, clay sand soaking in the upper part of the profile under the influence of rainwater, and the probable occurrence of tunnel valleys in the vicinity of the landslide, which create a slippery surface.  The main mining factors leading to the formation of landslide include: failure to keep a safe distance of the dredger to the mining walls, and mining by scooping the dry layer, producing a so-called “slide”, without properly isolating the dry and wet layer. The article also indicates that preventing landslides during beneath-surface mining consists, in particular, in designing the parameters of scarps and slopes, in order to guarantee their stability in specific geological-engineering conditions and in mining the deposit according to the technical design for mining beneath water surface. Particular caution should be exercised when mining deposits with diverse geological structures from under the water surface, i.e. when mining deposits with clearly diverse strength parameters and when the mineral is consolidated between the dry and soaked layer.  It was also noted that landslide phenomena are not easy to forecast, as they are usually formed by several factors acting in synergy.