Study On The Effective Area And Permeability Of Anisotropic Coal Blasting

The coal seam is heterogeneous due to the existence of bedding and cutting,which makes it anisotropic.The effective distance and permeability of coal seam in different directions are obviously different when blasting cracking is carried out in coal seam.In order to explore the characteristics of effective crack distance and permeability change of anisotropic coal seam,this paper takes the coal body of no.2 coal seam of zhaogu-2mine as the research object,and conducts the tensile and compressive strength tests along different directions to analyze the mechanical anisotropy characteristics of the coal body.Then,according to the anisotropic characteristics of coal mechanics,the rational distribution of holes in the coal seam is conducted,and the effective area of blasting cracking is tested in the field,so as to observe the changes of gas extraction concentration and purity in the coal seam before and after blasting cracking,and the effective area of blasting cracking is preliminarily determined.Then the dynamic mechanical characteristics of coal and the permeability before and after blasting impact are analyzed by SHPB active confining pressure test and permeability test.At last,the nonlinear software ls-dyna is used to simulate the blasting splitting process of coal seam.The effective blasting splitting area and its permeability change characteristics of anisotropic coal seam are determined by the combination of experiment and simulation.The main conclusions are as follows:(1)The blasting crack area is elliptic.With the blasting hole as the center,the effective splitting distance is 4.3 m in the direction parallel to the bedding and 2.6 m in the direction perpendicular to the bedding.(2)The maximum dynamic strain rate of coal increases exponentially with the impact pressure.the dynamic strain rate of coal samples perpendicular to the bedding direction is obviously lower than that of coal samples parallel to the bedding direction.at the same impact pressure,the maximum stress value of coal samples perpendicular to the bedding direction is obviously higher than that of coal samples parallel to the bedding direction.(3)The permeability of coal seam decreases exponentially with the increase of the cracking distance under blasting impact.The coal seam permeability decreases rapidly in parallel to the bedding direction relative to the coal seam permeability perpendicular to the bedding direction.