Formation of gas- and water-impermeable area in a mine working roof with injection bolts

Abstract

Safety and efficiency of coal mining depend on natural geomechanical and hydrogeological conditions of mining operations. They initiate the processes of deformation and water and gas filtration in the cracked coal seams and host rocks. Abundant water and methane inflowing into the mine workings, as a rule, leads to accidents, increased downtime of longwall faces, reduced productivity and economic losses. One of the ways to prevent gas and water inflow is to create an impermeable zone in the rocks around the mine working with injection bolts. Formation of such zones depends on the filtration area size and the rock permeability inside this area. It is conditioned by the natural fracturing of the rocks and degree of their unloading during the technological cycle of the mine face advancing. The purpose of this work was to investigate the conditions for the formation of an impermeable area in the mine roof with using injection bolts. A numerical model of the coupled processes of rock deformation and filtration of liquid polymer components was used for investigating the rock permeability in the mine working roof depending on the number of injection bolts. The host rocks permeability was calculated for cases when one, three or five injection bolts were installed in the mine roof. It is shown that permeability of the roof rock around the injection bolt decreases when polymer solidification process begins and the metal tube starts to work as a roof bolt. Diameter of the created polymer-reinforced rock-bolt support reaches 2.0 m, for the accepted initial and boundary conditions. When number of the bolts is three the polymer-reinforced monolithic rock-bolt supports are not interconnected; they are separated by fractured, disturbed rock, while installation of five polymer-reinforced supports in the mine roof form a rock-bolt canopy, which is practically impermeable. That is why density of the injection bolts installation plays a significant role in the formation of the rock-bolts canopy. With the increase of the number of bolts from one to five, average value of the permeability coefficients in the mine working roof decreases by 4 times. The formed rock-bolts canopy can serve as a barrier that restrains water and gas inflowing from the undermined rocks into the mine working. Keywords: injection bolt, injection of the consolidating mixture, impermeable beam, numerical simulation of coupled processes.