Experimental Study On The Relationship Between Fracture Rate And Permeability Of Rock Strata In Different Parts Of Coal Mining Area

With the large-scale coal mining, a large area of mining out area was formed in mining area, resulting in underground rock stress re distribution and fracture rock mass damage. The damage causes a great change in the fracture rate and permeability of the rock mass. And then it causes the mining area to be covered by the aquifer to the mine leakage, which may cause the overlying aquifer to be drained, and the influence on the local life and production activities.However coal mining will encounter fractured rock mass seepage problem, thus goaf seepage characteristic of overlying rock research to promote the coal mine production safety. Therefore, the study of the seepage characteristics of the overlying rock in the goaf has important engineering practice value to promote the coal mine safety production and realize the sustainable development of coal mining and coal industry.In order to study the relationship between the fracture rate and permeability of strata in different parts of mined out area, in this paper, the similar simulation experiment was designed to study the development situation of overlying strata and fracture after the coal seam mining, and to analyze the fracture rate of the strata in different locations; again Based on the similar simulation experiment of the goaf, the model of the simplified fracture physical model is established. The experimental system of rock seepage and rock seepage in the goaf caving zone, the rock mass in the fracture zone of the goaf and the vertical seepage test system of the fractured zone in the goaf are designed. The permeability test system can test of mined out area in different parts of rock mass permeability. Finally, combined with model experiment results show that the fracture rate results, analyzed the relationship of mined out area in different parts of the rock cranny ratio and permeability.The main results are as follows:(1) According to the simulation results, The development law of overlying strata in coal seam mining is discussed, and the fracture distribution characteristics of "vertical three zone" and "horizontal three zone" are analyzed and described. And the fracture rate of rock strata in different parts of mined out area was statistically.(2) According to the goaf caving zone broken rock mass seepage characteristics experiment shows, the seepage hydraulic gradient and seepage velocity does not conform to Darcy’s law, which is a power curve. The permeability coefficient of the rock mass with different fracture rate in goaf is calculated.Experimental results also show that the permeability of the broken rock not only relates to the fracture rate, but also to the sample particle size and fracture structure.(3) According to the fracture of goaf with seepage characteristic experiment shows that, the seepage hydraulic gradient and seepage velocity are not consistent with Darcy’s law, also showed a power curve. And the permeability coefficient of rock mass in different parts of the goaf is calculated. The experimental results also show that the permeability of fractured rock mass is not only related to the fracture rate, but also to the fracture connectivity of the rock mass.(4) According to the fracture of goaf with seepage characteristic experiment results show that, The horizontal permeability coefficient and the vertical permeability coefficient of the same crack rate and fracture structure rock mass have obvious difference. The horizontal permeability coefficient is 20 times of the vertical permeability coefficient.