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**AustPADS Finite Element Method Based Pavement Response to Load Model**

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**Outline Introduction Finite Element Method Material characterisation**

APADS - Austpads & Hosted service Worked examples Making sense of the results

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Introduction

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**Background Current designs use CIRCLY to calculated critical strains**

CIRCLY is a layered linear-elastic modelling of materials cross-anisotropy GUI actively developed

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**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

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**Schedule Transitioning from CIRCLY to FEM Official implementation**

The journey started Official implementation Not before some years Staged implementation Linear elastic Nonlinear elastic

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**Finite element method Overview**

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**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

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**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

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**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

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**Laboratory materials characterisation**

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**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

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Overview of the GUI

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**Overview of the GUI Pavemt structure Load definition Traffic &**

Performance relationships Layer characteristics Thickness Material parameters Critical strain location

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Worked example

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**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

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**Unbound granular pavement: inputs**

Linear elastic Thicknesses Moduli Poisson’s ratio

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**Unbound granular pavement: outputs**

The calculation is running in the background

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**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

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**Making sense of the outputs**

LINEAR-ELASTIC Making sense of the outputs

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Unbound pavement

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**Asphalt surfaced unbound**

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**Asphalt surfaced unbound**

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**Making sense of the outputs**

NONLINEAR-ELASTIC Making sense of the outputs

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Full depth asphalt

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**Analysis types Linear–elastic Nonlinear-elastic**

Results very similar to CIRCLY Nonlinear-elastic Results different to CIRCLY Need updated/calibrated performance relationships

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**Further information Thank you**

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

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