Investigation and prediction of water infiltration process in cracked soils based on a full-scale model test

Desiccation cracks induce preferential flow in cracked soils, leading to water rapidly infiltrating into deep soils and filling from bottom to top in the cracks, thus potentially result in shallow landslides. The major objectives of this study were to investigate rainwater ponding and the infiltration process in cracked soils and to validate a new predictive model. A full-scale slope model test was conducted under rainfall-evaporation cycles. Desiccation cracks on the slope crest were photographed, where the water ponding time was recorded, and the crack patterns were quantified by image processing techniques. Crack depth was also measured by thin iron wire and flexible ruler. The moisture content and matric suction at different soil depths under the photographed area were monitored by hydrologic sensors, and their response time was recorded to identify the preferential flow and estimate the infiltration depth. Besides, an improved dynamic dual-domain preferential flow model based on classic Green-Ampt concepts was proposed to elaborate and predict the ponding as well as the infiltration process in cracked soils. The model incorporates 12 parameters. It can simulate water filling from bottom to top in the cracks and accounts for dynamics in desiccation crack properties without requiring the use of hydraulic parameters for the crack domain. The experiment results showed that crack closure degree and ponding time of the soil matrix decreased with rainfall-evaporation cycles. Rainwater can quickly infiltrate into slope even the cracks were nearly closed. Two preferential flows and seven sequential flows were recognized, and the maximum infiltration depth was about 120 cm with 30 cm crack depth during rainfall. Then, performance of the model was verified with the monitoring data. It provided satisfying estimations of the ponding time and wetting front depth with general root mean square deviations (RMSD) of 21.2 min and 109.6 mm, respectively. In conclusion, this model comprehensively captures the physical characteristics and hydraulic effects of desiccation cracks, which shows a great possibility of further applications and improvement.