Study on the Liquefaction Mechanism of Mixed-Size Tailings Material Based on Grain Contact State Theory

Tailings ponds serve as high-potential energy structures designed to store waste tailings and other industrial materials. However, they can give rise to significant environmental pollution and pose a substantial threat to social and economic development, as well as the safety of people's lives and property. Seismic disasters can cause liquefaction of tailings, leading to destabilization and dam failure of tailings ponds, and the evolution of dynamic pore pressure of tailings can indirectly reflect the destabilization process of tailings ponds. Fine grain content is one of the main factors affecting the dynamic strength and pore pressure development of tailings. This article studies the microscopic characteristics of tailings material through microscopic observation, triaxial testing, discrete element simulation, and grain contact state theory, aiming to analyze the influence mechanism of fine grain content on the micromechanics of tailings. Based on the grain contact state theory, the tailings with different fine grain contents are classified into three types: coarse grain tailings, intermediate-size grain tailings, and fine grain tailings, and the grain contact is classified into four different states. In contact state 1, the vibration pore pressure exhibits a "fast-stable" development mode with increasing vibrations. In contact state 2 or 3, the vibration pore pressure develops linearly with vibrations. For contact state 4, the development of vibration pore pressure presents a "fast-stable-sharp" development mode. The effect of fine grain content (FC) on the liquefication of the tailings studied in the present work is as follows. When the fine grain content is FC<30%, the liquefaction resistance of the tailings decreases with the increase of FC. When FC>30%, the liquefaction resistance increases with the increase of FC. When FC=30%, the liquefaction resistance is the lowest, indicating that the critical threshold of the fine grain content of the tailings studied in the present work is FCth=30%.