The effect of instrumentation on the determination of the resilient modulus of unbound granular materials using advanced repeated load triaxial testing

Unbound Granular Materials (UGMs) are used in the base/subbase layers of flexible pavement structures for the vast majority of the main roads around the world. The resilient modulus of UGMs is a key input parameter for the design and analysis of flexible pavement structures. In the present study, four road base UGMs with a range of moisture contents are used to evaluate each material's resilient deformation behaviour using laboratory repeated load triaxial tests. The triaxial system for the tests is instrumented with four axial deformation gauges: an on-specimen axial Hall-Effect transducer, an internal Linear Variable Differential Transformer (LVDT), an external LVDT, and the actuator LVDT. The application of a Hall-Effect transducer directly mounted on the specimen and the three LVDTs permits the comparative study of alternative deformation measurements for the determination of an accurate and reliable resilient modulus value. By comparing tests results obtained with each transducer, the relative capability of each measurement is determined and a reference transducer for deformation measurement is identified. A constitutive model is then used to carry out a regression analysis and to predict the resilient modulus of the four tested materials.