Model for predicting resilient modulus of unsaturated subgrade soil using soil-water characteristic curve

Soil suction (ψ) is one of the key factors that influence the resilient modulus (M R ) of pavement subgrade soils. There are several models available in the literature for predicting the M R –ψ correlations. However, the various model parameters required in the existing models are generally determined by performing regression analysis on extensive experimental data of the M R –ψ relationships, which are cumbersome, expensive, and time-consuming to obtain. In this paper, a model is proposed to predict the variation of the M R with respect to the ψ for compacted fine-grained subgrade soils. The information of (i) the M R values at optimum moisture content condition (M ROPT ) and saturation condition (M RSAT ), which are typically determined for use in pavement design practice; (ii) the ψ values at optimum moisture content condition (ψ OPT ); and (iii) the soil-water characteristic curve (SWCC) is required for using this model. The proposed model is validated by providing comparisons between the measured and predicted M R –ψ relationships for 11 different compacted fine-grained subgrade soils that were tested following various protocols (a total of 16 sets of data, including 210 testing results). The proposed model was found to be suitable for predicting the variation of the M R with respect to the ψ for all the subgrade soils using a single-valued model parameter ξ, which was found to be equal to 2.0. The proposed model is promising for use in practice, as it only requires conventional soil properties and alleviates the need for experimental determination of the M R –ψ relationships.