Equilibrium Suction Prediction Model for Subgrade Soils in Oklahoma

Abstract

A rational method for estimating soil suction variations within the so-called moisture active zone or vadose zone is required. Within the unsaturated zone, a soil suction envelope is defined by the maximum and minimum suctions at the ground surface (i.e., the suction amplitude), equilibrium suction, and depth to the equilibrium (or constant) suction. This paper presents a mechanistic-numerical model for predicting equilibrium suction that takes into account the effects of the diffusion coefficient and makes use of surface field suction measurements. The rational attenuation function in this study represents the rate of suction change within the unsaturated zone. The model can predict the equilibrium suction in response to changes in the subgrade moisture regime. The geographic information system (GIS) platform was used to create contour maps of the mechanistic-numerical equilibrium suction values for Oklahoma. In addition, the paper presents a reliable statistical-based equilibrium suction prediction model based on readily available parameters such as Thornthwaite Moisture Index (TMI), clay content, and relative humidity.