Determining the Seepage Stability of Fractured Coal Rock in the Karst Collapse Pillar

Abstract

The karst collapse pillar (KCP) is a common geological structure in the coal mines of northern China. KCPs contain many fractured coal rocks, which can easily migrate under the action of high-pressure water. The destruction or instability of the cementation structure between the rocks can directly induce coalmine water-inrush accidents. To study the seepage stability of cemented and fractured coal rock under triaxial pressures, a self-designed triaxial seepage testing system was used and the permeability k and non-Darcy factor β of the cemented and fractured coal rock were tested. Furthermore, the 1D non-Darcy seepage equations were used to calculate the evolution criteria of the seepage loss stability. The results show the following: (1) The cemented structure in the KCP under the triaxial pressures can be easily destroyed. The damaged coal and rock body mainly exists in bulk form, and the permeability depends mainly on the effective stress of the particles. (2) The seepage process in the KCP structure is a combination of pore flow, fracture flow, and pipe flow, and the transition of the seepage state is closely related to the change in the magnitude of β. (3) Under the long-term effect of confined underground water, the migration of small fractured particles in the KCP will increase the structural porosity. If the parameter βk2 reaches the threshold value, the seepage system will evolve into a pipeline flow state, eventually causing a water-inrush accident.

Experimental study on the permeability of crushed coal medium based on the Ergun equation

“…A large number of studies have shown that the flow of gas in crushed coal bodies can be divided into three zones 28 : (1) Low Reynolds number zone: Re < 10, wherein viscous drag dominates, classifying it as the linear laminar flow region, wherein the flow follows Darcy’s law; (2) medium Reynolds number zone: 10 < Re < 100, wherein viscous resistance dominates, classifying it as a non-linear laminar flow region, wherein non-linear permeability behaviour predominates; (3) A high Reynolds number zone: Re > 100, wherein turbulent flow occurs, inertial forces dominate, and the flow resistance is proportional to the square of the flow velocity. The Re number is shown in Fig.…”

Re-crushing process and non-Darcian seepage characteristics of broken coal medium in coal mine water inrush

“…By studying the flow characteristics of porous rock media under pressure, Ma et al 13 proposed a logarithmic equation between axial pressure and permeability coefficient. By studying the effect of external compressive stress on the seepage characteristics of granular coal, Ma et al 14 and Zhang et al 15 found that at higher compression rates, the strength of particle breakage is greater. As the porosity of the sample gradually decreased, Wu et al 16 and Ma et al 17 believed that particle breakage during compaction was the main reason for the generation of tiny particles, which would show a non-Darcian seepage state.…”

Stability Assessment of Ground Surface along Tunnels in Karst Terrain Using Improved Fuzzy Comprehensive Evaluation

“…Because of the complex karst phenomena, the ground collapse in karst terrain has the characteristics of invisibility, burstiness, and mass occurrence [1,2]. Once the ground collapse happens in the karst terrain, it may cause great casualties and economic losses [3][4][5][6][7]. Recently, more and more efforts have been made in the development and utilization of underground space, and thousands of tunnels have been constructed in karst terrain all over the world, resulting in the fact that hundreds of ground collapses caused by tunnel construction have happed [8][9][10].…”