Influence of freeze–thaw cycling on the soil mechanical properties of open-pit mine dump under different moisture contents

Abstract

Freeze–thaw circulation under different moisture contents is the main influencing factor of the soil strength characteristics at a dumping site. The fine-grained sand materials of an internal dumping site in the Yuanbaoshan open-pit mine of China were selected as the research object; the changes of soil strength and deformation characteristics of 5 types of freeze–thaw (F–T) cycles were studied under 8 types of moisture contents. The stress–strain curve of soil sample shows strain hardening after different F–T cycles. The shear strength of the soil material decreases unevenly with increasing number of F–T cycles, and the greatest decrease in the shear strength occurs after the first F–T cycle. Under the condition of the same F–T cycles, the cohesion and internal friction angle (shear strength parameters) of the soil material decrease nonlinearly with increasing moisture content and decay in the form of a power function. For the same moisture content, the effect of F–T cycling on the internal friction angle of the soil is small, but the cohesion of the soil decreases as the number of F–T cycles increases, eventually stabilising. A quadratic polynomial equation can accurately describe the quantitative relationship between the cohesion and number of F–T cycles, at the same time, the unified regression equations of cohesion, moisture content and F–T cycle are established. The research results provide an important idea for the design of dumps and slope stability analysis, especially for the first year after dumping.