No abstract

Hydraulic fracturing is an effective mean to prevent coal bumps in deep coal mining. The calculation of stress redistribution of coal sidewall after hydraulic fracturing can evaluate the fracturing effect and provide a reference for the hydraulic fracturing scheme design. In this paper, a theoretical model of stress redistribution of roadway sidewall after hydraulic fracturing is established with considering the effect of crushing zone. And the influences of the water injection length and the fracturing radius on the stress redistribution of roadway sidewall are investigated. The results show that the water injection section should be set at a deeper position with considering the existence of the crushing zone. The coal roadway sidewall after hydraulic fracturing is divided into five zones: the crushing zone, the shallow plastic zone, the pressure relief zone, the deep plastic zone, and the elastic zone. The stress redistribution law is obviously affected by the water injection section length and fracturing radius. With the increase of water injection length or fracturing radius, the pressure relief effect is more evident, but the axial force of rockbolt increases gradually. In order to acquire a better pressure relief effect, the matching of the water injection length and the fracturing radius should be considered crucially in the hydraulic fracturing design for preventing coal bumps.

The energy supply effect caused by the stiffness difference between roofs and sidewalls is an important factor that induces strain coal bursts. In order to quantitatively reveal the energy supply mechanism of strain coal bursts, this paper first establishes a coal burst energy model of the rock–coal system and proposes the calculation formula of coal burst kinetic energy considering supply energy and the stiffness ratio of rock to coal. Then the whole energy evolution law of the rock–coal system with different stiffness ratios is researched by using the numerical simulation method, and the whole process is divided into three stages. With the decrease in the stiffness ratio, the elastic strain energy of the coal changes little, while its kinetic energy is negatively correlated with the stiffness ratio in a power function. Meanwhile, the elastic strain energy and kinetic energy of the rock have power function relations with the stiffness ratio, too. When the rock–coal system is fractured, the kinetic energy of the coal comes from the release of elastic strain energy from the coal and the energy supplied from the rock. The energy supply rate is between 22% and 35% when the stiffness ratio changes from 3.0 to 0.5, and they show a linear relationship, while the supplied energy has a negative power function relationship with the stiffness ratio.