Predicting the Repeated Load Behaviour of Pavement Subgrades Using the Three-surface Kinematic Hardening Model

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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

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Presentation Outline

• Introduction
• Finite element analysis of a 3-layer pavement
• Model predictions under cyclic loading
• Conclusions

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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

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Cross-section of a Pavement
Moving wheel load
Bituminous
Granular Sub-base
Subgrade
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FE Mesh

• 8-noded quadrilateral elements
• Wheel load of 600 kPa
• 50 cycles

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Results
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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

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Problem

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

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Model Predictions

• Simple triaxial simulation on isotropic normally
  consolidated soil
• Model parameters

M ? ecs ? G'ec (kPa) T S ?
0.89 0.073 1.994 0.008 60000 0.25 0.08 2.5

• 20 isotropic cycles with ?p' 100 kPa

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Results
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Results
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Problem

• Isotropically normally consolidated soil
• Accumulation of negative permanent shear strain
  for low stress pulses

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Results
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Results
u
u
u
u
u
u unloading
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Results

• Load pulses cycle in the way shown

Kinematic surface
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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