Climatic Wetting‐Drying Cycles Induced Microstructure Damage and Tensile Strength Deterioration in Near‐Surface Soil

Abstract Near‐surface soils are increasingly exposed to repeated wetting‐drying (W‐D) cycles under intensifying climate change. Such hydroclimatic fluctuations progressively degrade soil structure and mechanical properties, posing risks to the stability of earthen slopes and infrastructures. This study aims to investigate how climate‐driven W‐D cycles influence the tensile behavior and microstructural evolution of compacted near‐surface soils. Direct tensile tests were conducted on soil specimens after different number of W‐D cycles, followed by measurements of water content, void ratio and suction. Microstructural changes were analyzed using mercury intrusion porosimetry. Results show that tensile strength decreases significantly with increasing W‐D cycles and tends to stabilize after three cycles. This reduction in tensile strength indicates a decreased resistance to crack initiation and propagation, making surface soils more susceptible to desiccation cracking under successive W‐D cycles. Microstructural analysis reveals a trimodal pore size distribution in soil specimens, characterized by macropores, mesopores and micropores. With continued cycles, macropores collapse significantly, micropores remain relatively stable, while mesopores and potential macrocracks unexpectedly increase. The soil microstructure approaches an equilibrium state after three W‐D cycles. Based on these observations, a physically meaningful damage coefficient is proposed to quantify climate‐induced microstructural damage. A concise predictive model incorporating this coefficient is developed and validated to describe the evolution of tensile strength. These findings provide microstructural insights into the climate‐driven mechanical degradation of near‐surface soils, with broad implications for cracking, erosion, and shallow instability of earth structures under a changing climate.