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Correlation between deflections measurements on flexible pavements obtained
under static and dynamic load techniques
Corrélation entre les déflexions de revêtements flexibles mesurées sous chargement statique et
dynamique
Murillo Feo C.A.
Ph.D., Civil Engineering, Department of Civil and Agricultural Engineering. Universidad Nacional de Colombia, Av. NQS 45-03
Bogotá, Colombia
Bejarano Urrego L.E.
Civil Engineering, Universidad Nacional de Colombia, Av. NQS 45-03 Bogotá, Colombia.
ABSTRACT: Over the last 40 years several nondestructive techniques have been developed for determining the structural capacity of
flexible pavements as a function of the deflections produced by the application of a load. The techniques most used in Colombia to
measure pavement deflections are the Falling Weight Deflectometer (FWD) and the Benkelman beam, the first one works under dynamic
loading and the second device under static loading. However, for over 10 years, the use of devices under static loading has not been
recommended by several design methodologies, including AASHTO, but these are still used widely in many countries, for this reason it
was necessary to establish the correlation between the deflections obtained from FWD and Benkelman beam, specially on deteriorated
pavement structures; for this purpose, it was selected a section of flexible pavement road with presence of different types of deterioration.
The influence of type of deterioration, the temperature of the asphalt layer and the presence of nearby drainage structures and vegetation in
the measurements were evaluated. The obtained results showed that both devices have high correlation, and it is possible to obtain FWD
deflections as a function of Benkelman beam deflections.
RÉSUMÉ : Dans les quarante dernières années plusieurs techniques ont été utilisées pour déterminer la portance des chaussées en utilisant
les bassins de déflection générée par l’application d’une charge. Le déflectomètre FWD est devenu aujourd'hui l’appareil de référence in-
ternational pour la détermination de la portance des chaussées. Cependant, en Colombie, la poutre Benkelman est la technique plus utili-
sée, bien que l’utilisation d’appareils sous charge statique n’ait pas été recommandée par plusieurs méthodologies. Par conséquent, il était
nécessaire d’établir la corrélation entre les déflexions obtenues à partir de la poutre Benkelman et le FWD. Plusieurs tests ont été menés
afin de réaliser la comparaison entre les déflections obtenues par la charge statique ainsi que la charge dynamique. Les essais ont été réali-
sés sur chaussée souple avec différents types de détérioration. L’influence du type de déficience, la température, la végétation ont été pris
en compte. Les résultats ont montré qu’il est possible d’établir une corrélation entre les deux appareils.
KEYWORDS: Non-destructive test, Benkelman beam, FWD, deflections, flexible pavement, structural number, resilient modulus,
backcalculation.
1
INRODUCTION
Most of the road network in Colombia has a significant level of
deterioration and therefore requires major rehabilitation projects;
in general, most of these rehabilitation activities involve a new
asphalt layer on the original pavement structure; knowledge and
analysis of structural capacity of the pavement is essential to
perform a durable and economical rehabilitation design.
It is possible to quantify the structural capacity of the pavement
by means of the structural number (SN), which, in this case, is
obtained in function of the deflections generated on the surface of
the pavement by a process of backcalculation. The most used
equipment in Colombia for measuring deflections on pavement
structures are the Falling Weight Deflectometer (FWD) which
works under dynamic loading and the Benkelman beam which
works under static loading.
The Benkelman beam was one of the first methods developed
for measuring deflections on pavements, is economical, readily
available and has been widely used in the world, however, its
performance is slow, has high degree of uncertainty taking data
and mainly it operates under a static load which does not really
represent the effects exerted by moving vehicles, presenting low
reliability of results. On the other hand the FWD, although it is
more expensive, has a high performance, is automated and
operates under a dynamic load, this is the most efficient
equipment and advanced technically exists to measure the
deflections of a pavement structure simulating the action of a
moving load.
Different associations like the AASHTO do not recommend
the use of deflectometers under static load, but in several
countries, including Colombia which presents damage in the most
of the road network, these devices are still in use especially the
Benkelman beam, not only for structural evaluation but also for
design of pavement structures; this is due especially to difficult
acquisition, unfamiliarity and cost of falling weight deflectometer.
