Investigation on the Fracturing Permeability Characteristics of Cracked Specimens and the Formation Mechanism of Inrush Channel from Floor

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.

A state-of-the-art review on rock seepage mechanism of water inrush disaster in coal mines

“…The simulation results show that with the increase of water pressure, the confining pressure decreases, while the permeability of the floor increases, and the fractures' penetration and water inrush occur at the stress change position. Wang et al (2021) established a numerical model and analyzed the fracture and hydraulic properties of fractured specimens. It is found that the permeability of floor strata is closely related to the horizontal stress after coal mining, and the longitudinal propagation of wing fractures contributes to the formation of water inrush pathways.…”

Water Inrush Mechanism of Roof Induced by the Fault Weakening Effect in the Coal Mining

“…Zhang et al [28] simulated the hydraulic fracturing and studied the evolution law of crack propagation and acoustic emission by RFPAflow. Wang et al [29] used RFPA-flow to study the influence of confining pressure and pore pressure crack propagation and permeability of rock mass under uniaxial compression and, on this basis, analyzed the formation mechanism of floor water inburst channel.…”

Thermal-Hydraulic-Mechanical (THM) Coupling Behaviour of Fractured Rock Masses

“…Fractured rock masses are rich in defects of different scales, including pores, microfractures, joints/fractures, and macroscopic discontinuities; the presence of these defects changes the mechanical properties of the rock masses to some extent (deformation modulus and strength parameters are reduced, and the rock masses are anisotropic) and also affects the permeability characteristics of the rock masses [1][2][3]. Along with the increased exploitation of underground space, the geological environment in which the deep rocks are located is special, presenting mechanical characteristics such as high in situ stress, high ground temperature, and high karst water pressure.…”