In-Situ and Numerical Investigation of Groundwater Inrush Hazard from Grouted Karst Collapse Pillar in Longwall Mining

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.

Hydraulic Behavior of Karst Aquifers

“…Constant exchange of best practices, technological progress, and new ideas in this engineering segment, connected with interactions of karstic groundwater and underground constructions, continues also in our Special Issue. Three papers presented here aimed at detailed groundwater monitoring for underground structures in karsts [14], formulation of evolutionary laws on water inrush from the cavity [15], and description of the reverse fault control mechanism in the development of underground rivers [16]. Although these do not cover the entire spectrum of underground engineering problems in karsts, but due to their presence in this Special Issue, they can be considered as new gems in the mosaic of karst geotechnics.…”

“…The potential aggressiveness of karstic groundwater toward the concrete lining of the Pirot Hydropower Plant water-conveyance tunnel (southeastern Serbia) was revealed by detailed monitoring in these complex geologic/hydrogeologic conditions [14].Čokorilo Ilić et al [14] performed their studies both inside the empty water-conveyance tunnel and, depending on the power plant operating regime, at observation wells along the tunnel, springs, and a stream in the vicinity of the tunnel. Apart from the water's aggressiveness toward the tunnel concrete lining, observations of the quantitative parameters pointed out hydraulically critical tunnel zones.…”

Numerical investigation of flue gas injection enhanced underground coal seam gas drainage

“…Wang et al determined the diffusion coefficient of CO 2 and CH 4 diffusion in coal. Ma et al analyzed the influence of groundwater migration on the mechanical properties of coal seam. Wang et al studied the microscopic structure, coal deformation, gas and water transport behaviors in heterogenous coal by CT three‐dimensional reconstruction.…”

Numerical Simulations of Fracture Propagation in Jointed Shale Reservoirs under CO2 Fracturing

“…The large consumption of water will restrict the oil and gas reservoir developments in a water-deficient area [8,9]. Second, due to the large amount of water and chemical reagents used in the hydraulic fracturing, it may cause potential water pollution and chemical pollution if the treatment of flowback fluids with chemical reagents is insufficient [10][11][12]. Third, for the reservoirs containing clay minerals, the permeability may decrease after water injection, thereby decreasing the production of gas reservoirs [13][14][15].…”