1. School of Civil Engineering University of Nottingham Predicting the Repeated Load Behaviour of Pavement Subgrades Using the Three- surface Kinematic Hardening Model By K.W. Hau, G.R. McDowell, G.D. Airey and S.F. Brown

2. Presentation Outline Introduction Finite element analysis of a 3-layer pavement Model predictions under cyclic loading Conclusions

3. Introduction Current pavement design methods are empirical based Objective: apply fundamental soil mechanics principles to pavement engineering FE analysis of 3-layer pavement Capability of the 3-SKH model in predicting soil behaviour under cyclic loading

4. Cross-section of a Pavement Bituminous Granular Sub-base Subgrade Moving wheel load

5. FE Mesh 8-noded quadrilateral elements Wheel load of 600 kPa 50 cycles

6. Results

7. Problem Common nodes at the subgrade interface Elastic layer will pull the soil in tension Overcome by applying equivalent stress Permanent strain obtained by assuming the top two layers will follow the surface of the clay

8. Problem Comparison between CRISP and layered elastic theory The 3-SKH model poorly predicts shear strain under low stress pulses

9. Model Predictions Simple triaxial simulation on isotropic normally consolidated soil Model parameters M * e cs ** G' ec (kPa)TS  0.890.0731.9940.008600000.250.082.5 20 isotropic cycles with  p' =100 kPa

10. Results

12. Problem Isotropically normally consolidated soil Accumulation of negative permanent shear strain for low stress pulses

13. Results

14. u u u u u u = unloading

15. Results Load pulses cycle in the way shown Kinematic surface

16. Conclusions The 3-SKH model predicts essential features of soil behaviour under cyclic loading Poor prediction of shear strain for small stress pulse Should not be a serious problem in pavement modelling