Predicting the Repeated Load Behaviour of Pavement Subgrades
Predicting the Repeated Load Behaviour of Pavement Subgrades Using the Threesurface Kinematic Hardening Model By K. W. Hau, G. R. Mc. Dowell, G. D. Airey and S. F. Brown School of Civil Engineering University of Nottingham
Presentation Outline • Introduction • Finite element analysis of a 3 -layer pavement • Model predictions under cyclic loading • Conclusions
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
Cross-section of a Pavement Moving wheel load Bituminous Granular Sub-base Subgrade
FE Mesh • 8 -noded quadrilateral elements • Wheel load of 600 k. Pa • 50 cycles
Results
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
Problem • Comparison between CRISP and layered elastic theory • The 3 -SKH model poorly predicts shear strain under low stress pulses
Model Predictions • Simple triaxial simulation on isotropic normally consolidated soil • Model parameters M * ecs * 0. 89 0. 073 1. 994 0. 008 G'ec (k. Pa) 60000 T S 0. 25 0. 08 • 20 isotropic cycles with p' =100 k. Pa 2. 5
Results
Results
Problem • Isotropically normally consolidated soil • Accumulation of negative permanent shear strain for low stress pulses
Results
Results u u u = unloading
Results • Load pulses cycle in the way shown Kinematic surface
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
- Slides: 16