Research Progress on the Evolution Characteristics of Engineering Properties of Expansive Soils in Complex Environments

Expansive soils are widely distributed in regions such as Anhui,Henan,and Yunnan in China.Their characteristics of swelling upon water absorption and shrinking upon water loss pose significant safety risks to the health and maintenance of various structures.Coupled with the impact of complex environmental conditions,these soils lead to substantial and often unpredictable damage in engineering projects.In recent years,to mitigate these risks,scholars have conducted extensive research.This paper reviews the evolution of the engineering properties of expansive soils under three environmental conditions:wetting-drying cycles,freeze-thaw cycles,and combined wetting-drying-freeze-thaw cycles.Through tests such as permeability,water absorption-swelling,and triaxial shear,the study analyzes changes in the physical and mechanical behavior of expansive soils during these processes.Using techniques like Scanning Electron Microscopy (SEM),X-ray Diffraction (XRD),and water vapor adsorption-desorption tests,the paper examines the microstructural response of expansive soils to environmental factors.Additionally,it summarizes the transformation of macro- and micro-level physico-chemical properties under complex conditions,including shear strength,internal friction angle,cohesion,micropore changes,and fissure formation.The study also reviews the influence of environmental factors like acid rain,heavy rainfall,and temperature changes on expansive soils,providing insights into the mechanisms underlying these changes.