AustPADS Finite Element Method Based Pavement Response to Load Model

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

Introduction

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

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

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

Finite element method Overview

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

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

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

Laboratory materials characterisation

Presumptive model parameters Austroads project TT1452 developed presumptive model parameters: Report AP-T199-12 (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

Overview of the GUI

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

Worked example

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 0.45 500 314 198 125 79 50

Unbound granular pavement: inputs Linear elastic Thicknesses Moduli Poisson’s ratio 500 314 198 125 79 50

Unbound granular pavement: outputs   500 314 198 125 79 50 The calculation is running in the background

Unbound granular pavement: outputs Critical strain (CIRCLY output +/- 0.3%) 500 314 198 125 79 50 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

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

Unbound pavement

Asphalt surfaced unbound

Asphalt surfaced unbound

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

Full depth asphalt

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

Further information Thank you Seek me out today. 26th ARRB Conference paper (Bodin et al). www.arrb.com.au/ARRB-Conferences Austroads Report AP-T199-12 www.arrb.com.au Thank you