Response analysis of subgrade soils using signal phase shift obtained from laboratory lightweight deflectometer tests

Abstract

Over the past decades, the use of fast and reliable measurement techniques of soil mechanical properties has gained popularity. The lightweight deflectometer (LWD) is among the tools developed that can allow one to determine the elastic modulus of soil. Viscosity response components in pavement or soil typically induce phase shifts between stress and strain peaks, which can be translated to phase angle. Subgrade soil may exhibit varying response types depending on its nature and characteristics. Using large laboratory subgrade samples, an experiment was designed to measure the elastic modulus and phase angle with an LWD in different stress and humidity conditions. A model associating the elastic modulus inferred from LWD tests with parameters describing stress, water content and soil properties was proposed. This model is fundamentally inferred from the relationship between elastic modulus and phase shift, and was used to assess the relative contribution of varying conditions on soil stiffness.