Expansion of Water Inrush Channel by Water Erosion and Seepage Force

Abstract

Water and mud inrush is a common geological disaster in the construction of karst tunnels. The loss of soil particles in filling-type karst disaster-causing structures is the key factor leading to the expansion of the water inrush channel. Considering the effects of water erosion, seepage force, and soil cohesive force, three-dimensional force analysis for soil particles on the side wall of the water inrush channel is conducted. The critical condition of incipient particle motion is established. The incipient flow velocity for sliding instability and rolling instability of the particle is deduced, respectively. The criterion of incipient particle motion is proposed. The expansion mechanism of the water inrush channel is revealed. The influencing factors of the incipient flow velocity are analyzed and the rules of particle loss are discussed. Finally, through the analysis of particle–fluid coupling and calculation of discrete element method (DEM)–computational fluid dynamics (CFD) coupling, numerical simulation for the incipient particle motion and channel expansion is implemented, and the proposed mechanism of incipient particle motion is verified. The results show that: (1) the incipient flow velocity of rolling instability is obviously greater than that of sliding instability; (2) the incipient flow velocity first decreases and then increases with the increasing particle radius and dip angle of the inclined plane; (3) the incipient flow velocity decreases linearly with the increase of hydraulic gradient and porosity; and (4) in the expansion of the water inrush channel, the incipient flow velocity of most particles is the critical flow velocity of rolling instability, while the incipient flow velocity of a few particles is the critical flow velocity of sliding instability.