Crack evolution and strength deterioration of fine-grained tailings under dry and wet cycle

Abstract

Affected by repeated tailings discharge and rainfall, tailings materials are constantly in a state of moisture absorption and desorption, which degrades mechanical properties of tailings. To investigate the evolution of cracks and the deterioration of strength in fine-grained tailings under dry-wet cycling conditions, direct shear tests and nuclear magnetic resonance (NMR) tests were conducted. The strength deterioration and pore structure characteristics of fine-grained tailings were analyzed. Using image processing technology, surface crack parameters of fine-grained tailings were extracted, and the crack evolution characteristics under dry-wet cycles were explored. The evolution of surface cracks can be divided into two stages: rapid crack development and steady crack development. In the rapid crack development stage, both the area and average width of the cracks decrease significantly, while the total length decreases slowly. In the steady crack development stage, the crack area and average crack width gradually decline, and the total crack length undergoes a pronounced reduction. The porosity of the tailings consistently increases due to the cycles. Cohesion and the internal friction angle of the tailings decrease exponentially with increasing porosity, and both also decrease as the number of dry-wet cycles increases. Consequently, the safety factor of the tailings dam gradually declines with increased cycling, leading to reduced dam stability and increased risk for safe operation. The research results provide certain guiding significance for the stability and long-term safe operation of tailings dams.