Water–rock two-phase flow model for water inrush and instability of fault rocks during mine tunnelling

Abstract

Water inrush hazard is one of the major threats in mining tunnel construction. Rock particle migration in the seepage process is the main cause of water inrush pathway and rock instability. In this paper, a radial water–rock mixture flow model is established to study the evolution laws of water inrush and rock instability. The reliability of the proposed model is verified by the experimental data from a previous study. Through the mixture flow model, temporal-spatial evolution laws of different hydraulic and mechanical properties are analysed. And the proposed model’s applicability and limitations are discussed by comparing it with the existing water inrush model. The result shows that this model has high accuracy both in temporal evolution and spatial distribution. The accuracy of the model is related to the fluctuation caused by particle migration and the deviation of the set value. During the seepage, the porosity, permeability, volume discharge rate and volume concentration of the fluidized particle increase rapidly due to the particle migration, and this phenomenon is significant near the fluid outlet. As the seepage progresses, the volume concentration at the outlet decreases rapidly after reaching the peak, which leads to a decrease in the growth rate of permeability and porosity, and finally a stable seepage state can be maintained. In addition, the pore pressure is not fixed during radial particle migration and decreases with particle migration. Under the effect of particle migration, the downward radial displacement and decrease in effective radial stress are observed. In addition, both cohesion and shear stress of the rock material decreased, and the rock instability eventually occurred at the outlet.

The Physical Behavior of Protected Coal Seams Based on Triaxial Unloading Conditions

“…Numerous scholars have conducted extensive research into the brittle nature of rock, and several rock brittleness indicators have been proposed based on rock strength indicators, stress-strain curves, and rupture angles. Zhang et al [46] proposed a new brittleness index for studying rocks by considering the joint influence of the pre-and post-curve peaks on the degree of rock brittleness, as shown in Equation (27). Based on this, the brittleness-ductility characteristics of the conventional triaxial tests and unloaded coal bodies were analyzed, as shown in Figure 10.…”

“…At the same time, laboratory physical similarity simulation tests have also been widely used to study the mechanical properties and damage characteristics of the overlying coal seams during protective seam mining, which is also the most common approach adopted when providing reference values for practical engineering [23][24][25]. Compared to a single research approach, a combination of multiple approaches is more convincing and can better serve the actual project [26][27][28]. The unloading effect of protective seam mining on the protective seam is affected by many factors.…”