Exploration of a mechanistic model for the quantification of the resilient modulus using free-free resonant column testing

Resilient modulus (MR) is one of the key properties used to characterise and quantify the mechanical behaviour of soil materials for pavement design purposes. Standard MR test procedures are often complex, lengthy, and cost-prohibitive for most routine daily applications. Therefore, correlative models relating to easy-to-obtain basic soil index properties, such as the Atterberg limits, have been historically used to predict and estimate MR; such index properties, however, are not always effective for obtaining correct MR values. Alternatively, the California bearing ratio (CBR) and nonlinear stress–strain constitutive models have also been used to estimate MR. The work presented in this paper proposes the implementation of an enhanced hyperbolic constitutive model (eHCM) for the estimation of MRbased on small-strain modulus measurements from the free-free resonant column (FFRC) test. The proposed approach aims to circumvent some of the challenges and complexity associated with the lengthy MR laboratory testing. Using the Texas flexible pavements and overlays database (namely the DSS) as the data source, the research methodology included: (a) formulating and developing the eHCM, (b) estimating MR values using the eHCM model along with FFRC test measurements, (c) calibrating and validating the eHCM model using modulus measurements obtained through conventional MR testing, and (d) establishing statistical correlations between eHCM model parameters and routinely measured soil properties. Ten in-service highway test sections from the DSS, encompassing both granular (flex) base and raw subgrade soil materials, were used for the study. From the corresponding results and findings, the eHCM model was found to be satisfactory in terms of adequately quantifying the mechanical behaviour of granular base and subgrade soil materials, yielding coefficient of variation values comparable to the literature. Overall, the proposed eHCM model indicated promising potential as a viable alternative, surrogate, and/or supplement for rapid MR estimation based on simple and inexpensive field or laboratory small-strain modulus testing such as the FFRC.