Model for Predicting Resilient Modulus of Unsaturated Subgrade Soils in South China

Subgrade soils are often unsaturated and the resilient modulus (MR) of subgrade soils is usually subjected to the climate environment and traffic loading in the field. Therefore, the Matric Suction (MS) and traffic loading are considered to be two important parameters associated to the MR prediction model. To verify the MR prediction model, the MS of the typical subgrade soil were determined through the pressure plate test. In this study, the soil-water characteristic curves were also described using the Fredlund & Xing’s model. Then, the dynamic MR of the typical subgrade soil under various stresses and water contents was measured. After that, a new prediction model was proposed with the model variables including the minimum bulk stress, octahedral sheer stress and matric suction, and the validity of the new model was verified by previous research results. Finally, the correlations between the physical properties of subgrade soils including the percentage passing through the No. 200 sieve (0.075 mm), plasticity index, liquid limit, dry density and the regression coefficients of the new model were established. The results show that the new model can be used to predict the MR well, and it effectively solves the problem that the bulk stress is equal with a different combinations of the confining pressure and deviator stress. At the same time, the MR can be predicted much more easily with physical parameters of subgrade soils rather than conducting triaxial tests.