311 / 2018-05-03 18:06:24

Numerical simulation of borehole instability and failure types based on fluid-solid coupling dynamic model of coal-containing gas

Hoek-Brown failure criterion; GSI; borehole instability; failure mechanism; fluid-solid coupling model

矿井瓦斯与煤与瓦斯突出 > 煤矿瓦斯

In order to reveal the instability and failure mechanism of coalbed boreholes when drilling in soft coal seams containing high gas, hard and soft compound coal seams, and outburst coal seams, based on Hoek-Brown failure criterion, geological strength index (GSI), and the dynamic characteristics of porosity and permeability of coal containing gas, the plastic flow factor is introduced into the elastoplastic constitutive equations, and the fluid-solid coupling dynamic model is established. Then, the distribution law of plastic zones around boreholes with different coal structures under different side pressure coefficients (SPC) is discussed, and the instability and failure types of coalbed borehole are classified. Research results indicate that the distribution ranges of the plastic zones around boreholes decrease gradually with the increase of the GSI value under different SPC, and there is a typical power function relation between the radius of plastic zones and GSI values. However, the shapes of plastic zones vary according to different SPC and GSI values. When GSI value is smaller, the shapes are approximately shaped like fans, ellipses, and the letter “X” under different SPCs. Otherwise, the shapes are approximately shaped like circles, the letter “V,” and pans. The failure types of coalbed borehole can be divided into stress-controlled failure, structural plane-controlled failure, and coal and gas blowout in soft coal seams, which respectively occur in hard coal seams whose GSI values vary from 60 to 100, coal mass with moderate strength, whose GSI values vary from 30 to 60, and soft coal seams, whose GSI values vary from 0 to 30.