Seepage instability mechanism of water inrush channel in non-uniform filling-type karst tunnels under different fine particle contents

In order to investigate the frequent water and mud inrush disasters caused by seepage instability in filling-type karst tunnels, the seepage instability mechanism of the water inrush channel under different fine particle contents is studied by mechanical analysis, laboratory testing and numerical simulation in the non-uniform filling-type karst tunnels. Firstly, a mechanical seepage instability model of the water inrush channel under different fine particle contents is developed. Secondly, the incipient particle motion mechanical test is conducted under different fine particle contents. Thirdly, the incipient particle motion and seepage instability of the channel under different fine particle contents are simulated by the CFD-DEM coupling method. Finally, the derived formulas for the incipient flow velocity are applied to the Junchang project. The main findings include that: (1) There is a nonlinear variation trend between the incipient flow velocity and the particle size, the incipient flow velocity initially decreases and subsequently increases with the increase of the particle size. (2) The shear strength of the particles decreases with the increase of the fine particle content, and the cohesion of the particles increases with the fine particle content. (3) The variable shape of the water inrush channel under different fine particle contents increases with the incipient flow velocity, and decreases with the increase of the fine particle content. (4) The main mode of critical instability for the particles is rolling instability. The error between the theoretical incipient flow velocity and the experimental incipient flow velocity in rolling instability increases with the particle size.