1. AustPADS Finite Element Method Based Pavement Response to Load Model

2. Outline Introduction Finite Element Method Material characterisation
APADS - Austpads & Hosted service
Worked examples
Making sense of the results

3. Introduction

4. Background Current designs use CIRCLY to calculated critical strains
CIRCLY is a
layered linear-elastic modelling of materials
cross-anisotropy
GUI actively developed

5. Background Austroads PTF want greater flexibility
future design tasks
non-linear modelling of materials
Finite Element Method framework
provides headroom to grow
start a journey
Austroads developed FEM tool
linear-elastic materials
cross-anisotropy
nonlinear-elastic materials
simple interface

6. Schedule Transitioning from CIRCLY to FEM Official implementation
The journey started
Official implementation
Not before some years
Staged implementation
Linear elastic
Nonlinear elastic

7. Finite element method Overview

8. Pavement model: what for?
Objective: calculate the critical responses to be used for performance prediction (performance relationships) Pavement model = multi-layered structure + axle load
The pavement model is used to calculate the strains in the pavement material.
From theses critical strains the design life can be determined using the MATERIAL performance relationships
The pavement model is the combination of the pavement structure (layers, thicknesses, material modulus, Poisson’s ratio)
AND
Loading conditions (standard axle considered according to AGPT 02)
Critical strains locations
Current pavement model
Multilayered
Infinite in plane
Subgrade semi-infinite
Wheel-load = circular

9. Finite Element Method: Quick Overview
Finite element method (FEM) in pavement engineering
Available finite element packages (ABAQUS, …) are very general
Program developed by academics (Universities, Research organisations…)
2D-axi. FEM pavement model
Mechanical, static Hydraulic, Thermal analyses can be computed
3D FEM pavement model

10. Linear vs nonlinear analysis
Stress State
Modulus E 1
Linear elastic material
Stress State σ
Modulus
E(σ) 1
Nonlinear elastic material
𝐹 = 𝑲 𝑈
𝐹 = 𝑲 𝝈 𝑈
Stiffness matrix varies with the stress state (i.e. load)
 Iterative process
Stiffness matrix is CONSTANT

11. Laboratory materials characterisation

12. Presumptive model parameters
Austroads project TT1452 developed presumptive model parameters: Report AP-T (Austroads, 2012)
Base materials (High and normal quality crushed rock)
Subbase materials
Typical subgrades
Material
𝒌 𝟏 (MPa)
𝒌 𝟐
𝒌 𝟑
High quality base
250
1.0
-0.25
Normal quality base
220
Material
𝒌 𝟏 (MPa)
𝒌 𝟐
𝒌 𝟑
Upper granular subbase
175
0.9
-0.25
Lower granular subbase
150
0.8
Material
CBR (%)
𝒌 𝟏 (MPa)
𝒌 𝟐
𝒌 𝟑
Silt (ML) 2 10
0.0
-0.50 … 5 35
0.10
-0.35
Highly plastic clay (CH)
Silty/sandy-clay (CL/SC) 3 15 70
0.15
Sand (SW, SP) 85

13. Overview of the GUI

14. Overview of the GUI Pavemt structure Load definition Traffic &
Performance
relationships
Layer characteristics
Thickness
Material parameters
Critical strain location

15. Worked example

16. Unbound granular pavement: inputs
Sprayed sealed surfaced unbound granular pavement Subgrade design CBR = 5%
Material
Thickness (mm)
Sub-layers
thickness (mm)
Design modulus (Mpa)
Poisson’s ratio V = H (-) Ev
EV/EH
Sprayed seal surface - na
Unbound granular
475 95
500 2
0.35
314
198
125 79
Subgrade
Semi-infinite 50
0.45

17. Unbound granular pavement: inputs
Linear elastic
Thicknesses
Moduli
Poisson’s ratio

18. Unbound granular pavement: outputs 
The calculation is running in the background

19. Unbound granular pavement: outputs
Critical strain (CIRCLY output +/- 0.3%)
Moduli problem
(being fixed)
Thicknesses
Austroads method (AGPT Part 2 – Appendix K.1)
Critical strains from CIRCLY output:
Subgrade 906 μm/m midway between the loaded wheels

20. Making sense of the outputs
LINEAR-ELASTIC
Making sense of the outputs

21. Unbound pavement

22. Asphalt surfaced unbound

23. Asphalt surfaced unbound

24. Making sense of the outputs
NONLINEAR-ELASTIC
Making sense of the outputs

25. Full depth asphalt

26. Analysis types Linear–elastic Nonlinear-elastic
Results very similar to CIRCLY
Nonlinear-elastic
Results different to CIRCLY
Need updated/calibrated performance relationships

27. Further information Thank you
Seek me out today. 26th ARRB Conference paper (Bodin et al). Austroads Report AP-T199-12
Thank you