Key parameters of directional hydraulic fracture of hard roof

Hard roof is one of the main factors that inducing dynamic disasters in coal mines. As a new technology for controlling hard roof, directional hydraulic fracturing is lack of researches especially the key parameters and its determination method which severely restrict the industrial application of this technology. Based on the elastic plate and voussoir beam theory, the analytical stress solutions and fracture criterion of the hard roof are given in this paper. Four key parameters that total and fracturing thickness, sublevel fracturing thickness, maximum hanging roof after fracturing and the fracturing dip angle were put forward, at the same time the determination method and formula of the four key parameters were studied, the research results laid a foundation for the promotion applications of technology.