Comparison of Laboratory Resilient Modulus with Back-Calculated Elastic Moduli from Large-Scale Model Experiments and FWD Tests on Granular Materials

Abstract

A comparison is made between resilient moduli obtained from (i) a conventional small-scale resilient modulus test, (ii) a large-scale model experiment (LSME), and (iii) a falling weight deflectometer (FWD) in the field. The LSME is a large prototype-scale test simulating a pavement section. The FWD tests were conducted on a highway test section. All tests were conducted on a typical base course material and two granular industrial by-products used as subbase. Relationships between elastic modulus and bulk stress were derived from the LSME data by modeling the set-up as a nonlinear elastic layered system using the computer program KENLAYER. Elastic moduli were back-calculated from the FWD data using the program MODULUS. Reasonable correspondence between the elastic moduli measured at different scales was obtained when empirical corrections were made for strain amplitude using a backbone curve for granular materials and by matching stress levels. However, even when corrections are applied, the low-strain (or maximum) elastic modulus for the industrial byproducts inferred from the laboratory resilient modulus test tends to be lower (by a factor of 1.5 to 4) than the operative elastic modulus inferred from the LSME and the FWD tests. In addition, the minimum bulk stress provided by the laboratory resilient modulus test can be higher than the bulk stress existing in the field. In such cases, the elastic modulus at the field bulk stress can be estimated by extrapolation using a power function.