The Use of a Kinematic Hardening Model for Estimating Subgrade Stiffness in Layered-elastic Analyses

Abstract

It is well known that subgrade stiffness is dependent on stress level; it is not a simple function of California bearing ratio (CBR). A procedure for estimating the subgrade stiffness using a constitutive soil model based on critical state soil mechanics is proposed. The procedure uses a kinematic hardening model to establish stress changes in the subgrade due to the application of a wheel load. These stress changes are then applied to simulated triaxial samples of subgrade clay using the same model for a number of cycles to quickly determine appropriate resilient moduli for input to a multi-layered elastic analysis. Comparison of the resilient deformation predicted by the multi-layered elastic analysis with that determined rigorously using the full elastic–plastic analysis for the pavement, shows that the kinematic model can be used to estimate subgrade stiffness from simulated triaxial tests. The kinematic hardening model requires only eight parameters which can be determined from simple laboratory triaxial tests.

Keywords:

• Elasticity
• Plasticity
• Kinematic hardening
• Critical state soil mechanics

Acknowledgements

The authors are very grateful to Dr Amir Rahim of CRISP Technical Support, for modifying CRISP so as to be able to perform cyclic loading.