Study on the Mechanism of Changes in Matric Suction and Shear Strength Mediated by Microstructural Evolution of Loess Under Wetting-Drying Cycles

Abstract Loess is abundant in sol-based materials and water-absorbing mineral components widely distributed in the world, and its physical and mechanical properties are significantly influenced by the water environment. Under the condition of wetting-drying cycles, the mechanical properties of loess can deteriorate remarkably, which adversely affects the stability of loess engineering. To explore the water environment dependence relationship between matric suction and shear strength of loess under wetting-drying cycles, this paper conducts a series of experimental studies, including XRD test, Pressure Plate test (PPT) and Unsaturated Consolidated Drained Shear test (UCD). The research results show that: the hysteresis law of the matric suction - volumetric water content curve is jointly determined by the matching degree between the amplitude of wetting-drying cycles and the bound water range of soil, the swelling-shrinkage characteristics of clay minerals, and the cumulative effect of microstructural modification; owing to the compensating effect of matric suction on soil strength, the soil strength attenuation induced by wetting-drying cycles is mainly concentrated in the range where matric suction is lower than the air-entry value (s < AEV). On this basis, this paper constructs a Van Genuchten Extension Model that correlates matric suction with the number and amplitude of wetting-drying cycles. The research results can provide theoretical support for improving engineering durability and help avoid the problem of inaccurate parameters caused by the adoption of “static assumptions” in engineering design, thus having important practical reference value.