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BVFF nummer:
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BVFF 2019:2-02
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Projekttitel
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Utveckling av en enkel fältmetod för mätning av packbarhet och permanenta deformationer hos obundna väglager
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Projektledare/Kontaktperson
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Dina Kuttah
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Telefon
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013204245
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Utförarorganisation
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VTI
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Medutförare
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VTI
KUAB Konsult & Utveckling AB
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Bakgrund
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Many road and transport administrations including the Swedish transport administration (trafikverket, TRV) have paid a particular attention to find a simple and a time saving technique to evaluate the unbound layers quality and properties directly in the field during roads construction and to provide input parameters to the roads design software by a simple and quick field methods.
Road performance models are used to estimate the total number of allowable load repetitions that a pavement can operate without structural and functional failures. The performance models are related to the strains in the pavement layers and the adequacy of the pavement layer is obtained based on deflection measurements where the stiffness of individual layers is back-calculated. Field tests are carried out using nondestructive testing such as Falling Weight Deflectometer (FWD) and Plate Load Testing (PLT). Nowadays, the light weight deflectometer (LWD) has widely been used overseas and become more and more popular in quality assurance of roads due to its light weight and time saving procedures.
This in situ estimation of the unbound layers plastic deformations with respect to the applied loading and other environmental conditions will enable the defining of the weak points in the compacted layers during construction and estimate the expected pavements ruts (deformations) and the required road rehabilitating actions in the future.
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Sammanfattning
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Flexibla överbyggnads¬konstruktioner är globalt sett den vanligaste typen för transportinfrastruktur.
Flexibla konstruktioner är oftast dimensionerade med mekanistiska-empiriska metoder. Även om mekanistiska-empiriska metoder oftast ger acceptabel dimensionering så har de sina begränsningar. Materialmodeller med mekanistiska-empiriska metoder bygger på elastiska teorier och förutsätter elastisk respons från vägmaterial. Begränsningar av tillåtna spårdjup bör ta hänsyn till faktiska belastningsrelaterade permanenta töjningar från vägtrafiken.
Trafikverket är intresserade av att utvärdera obundna lagers "packbarhet" och kunna bestämma ackumulerade permanenta deformationer vid belastning med hjälp av en enkel och tidsbesparande teknik för fältförhållanden. VTI har i samarbete med KUAB AB utvecklad en unik lätt fallvikt (light weight deflectometer, LWD) som har använts för att på ett enkelt och effektivt sätt uppskatta viktiga parametrar för obundna materiallager nämligen dynamiska elasticitetsmoduler som kan användas i dimensioneringsprogram. Trots att den nyutvecklade svenska lätta fallvikten är multifunktionell, kan den inte mäta permanenta deformationer som orsakas av dynamiska laster ännu. Syftet med detta projekt är att kunna fortsätta utveckla denna svenska lätta fallvikt så att man ska kunna bestämma ackumulerade permanenta deformationer på obundna materiallager i vägar på plats under byggskedet.
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Förväntat resultat
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Conducting test data from simple field tests has been in focus for many roads’ construction companies, and traffic administrations among them TRV and its contractors.
In this context, VTI has implemented a field time-saving and cost-effective testing method for evaluating unbound layers quality and properties directly in the field and provide input parameters to the roads design software mainly based on mechanistic-empirical methods. The use of the developed LWD will reduce the gap between the testing methods of unbound materials required in the pavement design software and those used in the field by roads contractors for compaction control. Even though mechanistic-empirical methods for roads design give a realistic design approach than purely empirical one, there are some limitations associated to them. The material models of mechanistic-empirical methods are based on elasticity theory and they consider the elastic response of pavement materials. In fact, limiting the rutting in pavements based on the subgrade strain criterion does not consider the actual load-associated plastic strains; rather, it is based on performance prediction models. Correspondingly, this project (suggested in this application) is intended to develop further the Swedish LWD to measure the elastic and plastic surface deformations separately. The new LWD’s model will be used to describe the relationship between the plastic deformation of a specific unbound pavement layers and the axial stress level, moisture content, compaction degree, and loading frequency. As a result, the unbound layers compaction potential and the cumulative plastic deformation of each unbound layer can be estimated at the field.
This issue is of interest for the Swedish transport administration since the project will help in the adaptation of TRV regulations by developing simple and practical method to control the requirements on unbounds materials for roads built of local Swedish materials during construction.
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Plan för resultatspridning och implementering
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The results of this project will be published as peer-reviewed article(s) and as a VTI report. In addition, a seminar will also be organized to publish the project result among the corresponding stakeholders (experts from trafikverket and industry).
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Tidsramar
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Startdatum 2019-06-13
Slutdatum 2020-08-31
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