Finite element modelling for prediction of permanent strains in fine-grained subgrade soils

Roads are designed with good reliability to fulfil the long-term performance during the design period. In order to achieve an effective design, the long-term performance of pavements should be optimized during the design phase. One of the strategies is to develop models which are capable of predicting the long-term performance. This paper focuses on one of the most critical distress modes in flexible pavements, namely, rutting. The plastic strain of subgrade soils is modelled to quantify the amount of rut contributed from the subgrade. The deformation from the first loading cycle is incorporated in the elastoplastic theoretical framework based on the Drucker–Prager yield criterion. The proximity of deviator stress to the static failure limit of subgrade soils is considered to predict the amount of incremental plastic strains at each loading cycle. The model is implemented in the User Material Subroutine in the finite element program ABAQUS™. The prediction of plastic strains using the proposed model provides a good agreement with laboratory test with deviator stress level up to 50% of the static strength of the soil. The mobilisation of subgrade soils in pavements is normally low due to reduced stress magnitude at the subgrade level, which makes the proposed model in this study more appealing to understand the development of plastic strains in subgrade soils.