Soil micro-penetration resistance as an index of its infiltration processes during rainfall

Rainfall infiltration is one of the most important driving factors of geological hazards, ecological environment problems, and engineering accidents. Understanding the principle of soil wetting during rainfall infiltration and its influence on soil mechanical properties is crucial for preventing geological hazards. In this study, micro-penetration tests coupled with moisture monitoring were performed to investigate the infiltration process during wetting through the measured change in mechanical characteristics. Results show that penetration resistance increases in the deep layer gradually. With increasing infiltration time, the wetting front keeps moving downward, and its range becomes wider. A slight increase of the penetration resistance in the shallow layer (d <= 17.5 mm) is observed. However, the penetration resistance in the middle layer (22.5 mm <= d <= 32.5 mm) decreases firstly before a slight increase. In the deep layer (d >= 37.5 mm), the penetration resistance decreases continuously during infiltration. Based on the measured water content profile during infiltration, it is found that the evolution of soil mechanical characteristics is fully responsible by the infiltration-induced re-distribution of water content along depth. Generally, the penetration resistance decreases exponentially with increasing water content in the soil. When the water content is low, wetting can weaken soil strength significantly, whereas this effect diminishes when the moisture surpasses a certain threshold. The results highlight that the penetration curves and water content profile show close inter-dependency and consistency, which verifies the feasibility of using micro-penetration to investigate rainfall infiltration and wetting process in surface soil layer or laboratory small-scale soil samples. This method enables fast, versatile and high-resolution measurements of infiltration process and moisture distribution in soil. (C) 2022 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V.

Automated summary

Rainfall infiltration is a key factor in geological hazards, ecological environment problems, and engineering accidents. This study investigates the process of soil wetting during rainfall infiltration and its impact on soil mechanical properties through micro-penetration tests and moisture monitoring. The results show that as infiltration time increases, the wetting front moves downward and the range widens. The penetration resistance varies at different depths. The study also finds that the evolution of soil mechanical characteristics is influenced by the redistribution of water content along depth. The method of micro-penetration proves feasible for studying rainfall infiltration and wetting process in surface soil layer or laboratory small-scale soil samples.