There are many karst collapse columns in coal seam roof in the southern coal field in China, which are different from those in coal seam floor in the northern coal field, due to the stratum characteristics. The karst collapse column in coal seam roof tends to reactivate and conduct water and induce the serious water inrush disaster, when the karst collapse column communicates with the overlying aquifer. In order to reveal the evolution mechanism of water-conducting channel of collapse column in karst mining area of southwest China, the aquifers and water inflow rule in 1908 working face in Qianjin coal mine are analyzed. Besides, the particle size distribution and mineral component of collapse column are researched by the X-ray diffraction test and the screening method, which are the basis for researching the water inrush mechanism in karst collapse column. On this basis, the water inrush of roof collapse column under the influence of mining is researched by establishing the numerical calculation model with the UDEC numerical software. The results show that the water flowing into the 1908 working face comes from the Changxing formation aquifer and Yulongshan formation aquifer above the coal seam, and the proportion of coarse particles and fine particles in collapse column is 89.86% and 10.14%, respectively. With the advance of working face, the water-conducting channel connected the working face with the aquifer, or the surface is formed by collapse pits, karst caves, and collapse column. The research results can be treated as an important basis for the water-preserved mining in southern coal field in China.
The fault water inrush is a key factor which leads to tunnel construction in karst regions. Based on the fluid mechanics principles, the paper addresses a numer?ical coupled model for karst fault tunnel with COMSOL Multiphysics software. Besides, the Darcy law equation, Brinkman equation, and Navier-Stokes equation are inserted to stimulate the steady flow of aquifer, the non-linear seepage of fault and the free flow in tunnel excavating area in software, respectively. Then, the pres?sure and flow velocity in three flow fields are analyzed under different permeability ratios in numerical model. It is shown that the fault permeability is the key factor affecting water inrush, and that the pressure and flow velocity change visibly in adjacent domains between two flow fields.
In order to improve and restore the strength and stability of broken overburden caused by coal seam mining in underground, the grout containing aggregate is employed to backfill specific fracture space in rock strata, which is an important method to prevent the mine water leakage and roof collapse in working face. Therefore, the migration characteristics and restoration mechanism of grout containing aggregate in overburden fractures based on the CFD-DEM coupling model are researched in this paper. Specifically, the mechanical constitutive model of aggregate migration is obtained by mechanical analysis of particles and flow field, and the mechanism of aggregate flow and transport with grout in rock fracture is put forward. Besides, the coupled CFD-DEM model is built by numerical simulation software, and the transport process of grout containing aggregate in the fracture is numerically calculated. On this basis, the transport law and deposition characteristics of aggregate transport with grout are studied, and the inner mechanism of the change law is obtained. The research results indicate that the aggregate is gradually deposited by various “settlement forces” during the migration process. The smaller the particle size and density of aggregate are, the slower the deposition rate of aggregate particles and the longer the migration distance are. The aggregate with particle size of 3 mm and density of 3250 migrates 1.25 m to reach the maximum solid ratio of 12.9%. The settlement ratio reaches 100% after migration of 1.5 m, and the longest migration distance is 1450 mm. In addition, the solid ratio of each aggregate firstly increases and then decreases with its migration, which is analyzed from the perspective of aggregate deposition and concentration change. When the aggregate density of two particle sizes changes from 3500 to 3750, the aggregate migration distance is significantly reduced. The research results provide an important guiding significance for reasonably selecting aggregate parameters and optimizing the design of grouting holes in mining engineering.
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