Abstract
To study the fracture characteristics and the permeability change law of the cracked specimens during the complete stress-strain process, a mechanical model was constructed, from which different types of crack initiation angles were obtained. The crack inclination angles under uniaxial compression, confining compression, and confining tension, and the influence of confining pressure and pore water pressure on the crack propagation and permeability of rock mass were investigated and simulated with RFPA-Flow software using prefabricated crack models with crack initiation angles of 30°, 45°, and 60°. Furthermore, the formation mechanism of inrush channel from floor was qualitatively analyzed. The results indicated that the theoretical initiation angles of wing cracks, secondary coplanar cracks, and secondary inclined antiwing cracks were found to be 70.53°, 0°, and 123.8°, which were consistent with the simulation results. The crack propagation was mainly concentrated at the postpeak stage of the complete stress-strain curve, causing the peak of seepage velocity to lag behind the stress peak. For the case with a constant confining pressure, the rate of crack initiation and propagation to final failure was positively correlated with the internal pore pressure. For the case with a constant water pressure, the speed of crack initiation and propagation to final failure decreased first and then increased as the confining pressure increased. In addition, the longitudinal propagation of wing cracks and the increase in permeability were prone to occur in the low confining pressure zone, which induced the formation of water inrush channels. The research result provides an improved understanding for predicting and preventing water inrush disasters.
Highlights
To study the fracture characteristics and the permeability change law of the cracked specimens during the complete stress-strain process, a mechanical model was constructed, from which different types of crack initiation angles were obtained. e crack inclination angles under uniaxial compression, confining compression, and confining tension, and the influence of confining pressure and pore water pressure on the crack propagation and permeability of rock mass were investigated and simulated with RFPA-Flow software using prefabricated crack models with crack initiation angles of 30°, 45°, and 60°
The formation mechanism of inrush channel from floor was qualitatively analyzed. e results indicated that the theoretical initiation angles of wing cracks, secondary coplanar cracks, and secondary inclined antiwing cracks were found to be 70.53°, 0°, and 123.8°, which were consistent with the simulation results. e crack propagation was mainly concentrated at the postpeak stage of the complete stress-strain curve, causing the peak of seepage velocity to lag behind the stress peak
The crack propagates approximately in the direction parallel to the axial pressure, gradually propagates to the upper and lower end faces of the specimen, and forms a “wing crack” which destabilizes and fails. e evolution of pore water pressure is consistent with the crack propagation process, which implies that the evolution of pore water pressure in the longitudinal direction (y-direction) is greater than that in the transverse direction (x-direction). is facilitates the further propagation of the fracture in the fluid-solid coupling process and leads to a significant increase in longitudinal permeability
Summary
To study the fracture characteristics and the permeability change law of the cracked specimens during the complete stress-strain process, a mechanical model was constructed, from which different types of crack initiation angles were obtained. e crack inclination angles under uniaxial compression, confining compression, and confining tension, and the influence of confining pressure and pore water pressure on the crack propagation and permeability of rock mass were investigated and simulated with RFPA-Flow software using prefabricated crack models with crack initiation angles of 30°, 45°, and 60°. To study the fracture characteristics and the permeability change law of the cracked specimens during the complete stress-strain process, a mechanical model was constructed, from which different types of crack initiation angles were obtained. Erefore, studying the propagation and evolution of rock mass cracks and their permeability characteristics is the base for studying the formation of the floor water inrush channels during mining, and it is the key to correctly understand the mechanism of mine water inrush disasters. Brace and Bombolakis conducted a singlecrack uniaxial compression test using photoelastic material and glass to study the fracture characteristics of brittle rock materials, where only wing cracks are found, which is propagated in a curved path and paralleled the direction of compression loading, and no secondary cracks appeared [11]. The stress condition for the initiation of secondary cracks and the crack initiation angle were rarely discussed in the involved mechanical models
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