Hydraulic characteristics and fracture evolution of loess under wetting-drying cycles

The Loess Plateau is one of the most geologically hazardous regions in China. In recent years, frequent extreme rainstorms and prolonged droughts in the area have caused repeated dry-wet cycles in the loess within the groundwater fluctuation zone at the edges of loess tablelands, exacerbating landslide risks. This study conducts soil-water characteristic curve (SWCC) tests, saturated permeability tests, and crack evolution analyses on intact loess from the Jingyang South Tableland under varying dry-wet cycles. The results indicate that: (1) Dry-wet cycles shift the SWCC leftward, significantly reducing soil water retention capacity, while the saturated permeability coefficient follows an exponential growth pattern. (2) The Van Genuchten (VG) model effectively describes the SWCC of intact loess after dry-wet cycles. Based on variations in fitting parameters, a predictive SWCC model is established. (3) Dry-wet cycles dynamically reshape the SWCC by driving crack evolution, thereby altering loess seepage characteristics. The crack evolution process under dry-wet cycles is divided into three stages: formation, development, and healing. (4) The mechanism linking loess hydraulic properties and crack evolution is revealed: initial dry-wet cycles significantly degrade hydraulic properties and meso-structure, further promoting crack initiation and propagation through positive feedback. After multiple cycles, cracks reach a healing threshold, with meso-structural reorganization and cementation filling leading to crack stabilization.