Investigation of Non-Equilibrium and Dynamic Behavior of Soil Water Characteristic Curves through Field Monitoring

In this paper, soil water characteristic curves (SWCCs) were reconstructed through simultaneous field measurement of soil water content and suction value. The objective of this study was to evaluate whether field-based monitoring could capture the different SWCC paths in various seasons. Moreover, field measurement of SWCC makes it possible to quantify the hysteresis phenomenon, analyzes the effect of various temporal resolutions on SWCC, and highlights the differences in reconstructed SWCC for the same soil during various weather conditions. Field data from one expansive subgrade site in Texas, USA were collected through moisture and suction sensors over a 3-year monitoring period. Analyzing the rainfall and evapotranspiration data, three distinct wetting and drying cycles were identified which allowed correct discrimination of the cycles. The pattern of changes in SWCC was identified in the various wetting and drying cycles. While the field data was fitted through the Van Genuchten equation, variations of the unsaturated soil parameters ( α, n, m) were identified in various cycles. Air entry value indicator parameter α ranged from 0.05 to 0.11 kPa −1 while the slope of the SWCC curve parameter n value varied from 1.1 to 1.45. Comparing these results with previous studies, it was concluded that wetting and drying cycle parameters do not have any predefined correlation. However, these unsaturated parameters required for numerical modeling are dependent on the climatic events happening year-round.