Microscopic Mechanism and Evolution Model of Cracks Development in Expansive Soil under Rainfall-Evaporation Cycle

Abstract

This study investigated the cracking development of expansive soils under cycling conditions of rainfall evaporation using Nuclear Magnetic Resonance(NMR) testing and image analysis methods. The study examined both internal and surface perspectives and analyzed the impact of small and medium rainfall cycles on the fine-scale mechanism of expansive soils. The experimental results showed that micropores and small-medium pores transformed into macropores during the cycling process, and this transformation was directly related to the intensity of rainfall. Furthermore, the porosity of the expansive soil increased during moisture absorption and decreased during dehumidification. Additionally, as the number of cycles increased, irreversible pores formed, resulting in the dispersion and damage of soil samples. The surface cracking development was divided into four stages, with primary cracking development occurring more rapidly during cycles of moderate rainfall evaporation. The average width of cracks was used to quantify the degradation of soil samples, and a model was developed to predict the evolution of crack width with an approximate relative error of 20% between predicted and measured values. This study has significant theoretical and practical implications for understanding the mechanisms of deformation and damage in expansive soils.