Abstract
Groundwater inrush is a typical hydrologic natural hazard in mining engineering. Since 2000 to 2012, there have been 1110 types of mine groundwater inrush hazards with 4444 miners died or missing. As a general geological structure in the northern China coalfields, the karst collapse pillar (KCP) contains a significant amount of granular rocks, which can be easily migrated under high hydraulic pressure. Therefore, the KCP zone acts as an important groundwater inrush pathway in underground mining. Grouting the KCP zone can mitigate the risk of groundwater inrush hazard. However, the fracture or instability of the coal pillar near KCP can cause the instability of surrounding rock and even groundwater inrush hazard. To evaluate the risk of groundwater inrush from the aquifer that is caused by coal pillars instability within grouted KCP in a gob, an in-situ investigation on the deformation of the surrounding strata was conducted. Besides, a mechanical model for the continuous effect on the coal pillar with the floor-pillar-roof system was established; then, a numerical model was built to evaluate the continuous instability and groundwater inrush risk. The collective energy and stiffness in the floor-pillar-roof system are the two criterions for judging the stability of the system. As a basic factor to keep the stability of floor-pillar-roof system, the collective energy in coal pillar is larger than that in floor-roof system. Moreover, if the stiffness of floor-roof or coal pillar meets a negative value, the system will lose stability; thus, the groundwater inrush pathway will be produced. However, if there is a negative value occurring in floor-pillar-roof system meets, it indicates that the system structure is situated in a damage state; a narrower coal pillar will enlarge the risk of continuous instability in the system, leading to a groundwater inrush pathway easily. Continuous coal pillars show a lower probability of instability. Conversely, the fractured coal pillars have a greater probability of failure. The plastic zone and deformation of the roadway roof in the fractured coal pillar are larger than that of continuous coal pillar, indicating that the continuous coal pillars mitigate the risk of groundwater inrush hazard effectively.
Highlights
With the increase of mining depth, difficulty, and production for coal resource in China, the mining-induced hazard occurs frequently, such as the water inrush accidents
Due to the weakness of surrounding rocks within karst collapse pillar (KCP), the fracturing of the coal pillar near KCP can cause the instability of surrounding rock and the increase of the seepage ability, resulting in groundwater inrush hazard
Numerical investigation that is based on the theoretical model is usually a common and effective method to predict the variations that cannot be measured in the field condition
Summary
With the increase of mining depth, difficulty, and production for coal resource in China, the mining-induced hazard occurs frequently, such as the water inrush accidents. With the progress of water inrush the number of groundwater damage inrush accidents each year. With the progress of water inrush prevention, the number accidents in coal mines is declining. Since 2000 to 2012, 1110 types ofof groundwater damage accidents in coal mines isminers declining. 4444since miners or missed [2].of mine groundwater inrush accidents have reported, with 4444 miners diedmakes or missed disaster affects theinrush safe mining, causes major labor and economic loss, and a serious. Chinese scientists have made preventing fatal mine water inrush accidents. The overlying strata loses its stability, rock fragments fall into the cavitation space, and karst collapse pillar (KCP) is formed. A typical hazard-causing geologic structure,space, KCP and is widespread the coalfields of northern. As typical hazard-causing geologic structure, KCP is widespread the coalfields of northern.
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