Temporal changes of soil temperature with soil water content in an embankment slope during controlled artificial rainfall experiments

Monitoring of soil water behavior is crucial for the prediction of disastrous slope failures. To improve the ability of engineers to detect temporal changes in soil water content on a slope, we investigated whether or not soil temperatures, which are relatively easy to obtain, could be used as indicators of changes in the soil water content. In order to evaluate the relationship between changes in soil temperature and soil water content, the soil temperature and volumetric water content in a slope on an embankment were measured during controlled rainfall experiments using a large-scale rainfall simulator at the National Research Institute for Earth Science and Disaster Prevention in Japan. Soil temperature was measured with highly accurate sensors at depths of 0, 0.2, 0.4, 0.6, and 0.8 m at four sites on the slope. Volumetric water content was measured at depths of 0.2 and 0.5 m at two sites. The results showed that for many sampling sites the soil temperature increased with the volumetric water content once the rainfall began. Three types of soil temperature behavior were observed: 1) a steep rise, 2) a gradual rise, and 3) a negligible change. The relationship between the elapsed time from the start of rainfall to the start of soil temperature rise and volumetric water content rise implies that soil temperature monitoring using high-resolution sensors is a viable way to detect general volumetric water content behavior due to rainfall infiltration during various rainfall events. These results also indicate that soil temperature monitoring has the potential to improve the understanding of soil water behavior in a slope, which is dependent on rainwater infiltration.