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Performance verification of a geogrid mechanically stabilised layer
Vérification de la performance d’une couche stabilisée mécaniquement par une géogrille
Wayne M., Fraser I., Reall B., Kwon J.
Tensar International Corporation
ABSTRACT: As part of the study to evaluate performance of a geogrid stabilised unpaved aggregate base overlying relatively weak
and non-uniform subgrade soils, a controlled field study was conducted in Weirton, West Virginia, USA. A punched and drawn
polypropylene triaxial geogrid was installed at the interface between a soft clayey subgrade and crushed limestone. In-ground pressure
cells were used to monitor horizontal stress within the subgrade and base throughout subsequent compaction and traffic loading. The
results demonstrated that the lateral stress in the subgrade were approximately ¼ that of the control section and in addition, the
geogrid confines unbound aggregate leading to an increased lateral stress and a higher resilient modulus for the stabilised base layer.
To verify that these results are applicable to different subgrade and aggregate materials, additional full-scale field tests were
conducted in Salt Lake City, Utah, USA. A total of four pressure cells were installed in test section, at spacings of 2.6 and 2.9 metres
from the centerline and offset 3 metre parallel to the direction of travel. Pit run material was used as a base layer in this study. Pit run
gravel is unprocessed material that contains all sizes of rock. The results show that the horizontal pressures within the subgrade
created by both the static and live loading conditions were significantly reduced by using the geogrid whereas a >80% increase in
horizontal pressures were measured for the control section after placement of aggregate fill. Post-traffic trenching of the control
section found significant mixing of the subgrade materials, whereas very little intermixing of the subgrade materials was reported for
the stabilised section. This paper presents the results and analysis from these field studies. The results confirm that the geogrid
promotes improved aggregate confinement and interaction, leading to enhanced structural performance of the unpaved aggregate base.
RÉSUMÉ : Dans le cadre d’une étude pour évaluer la performance d'une géogrille pour stabiliser une couche granulaire non revêtue
sur des sols de fondation de faible portance et hétérogènes, une étude expérimentale in-situ a été réalisée à Weirton, Virginie-
Occidentale, Etats-Unis, Une géogrille triaxiale, fabriquée à partir d’une feuille de polypropylène perforée et étirée a été installée à
l’interface entre un sol de fondation argileux mou et une couche de concassé calcaire. Des capteurs de pression ont été installés dans
le sol pour mesurer la contrainte horizontale dans le sol de fondation et la couche de gravier pendant le compactage et la circulation.
Les résultats ont montré que la raideur latérale dans le sol de fondation était approximativement le quart de celle de la section de
contrôle et par ailleurs, la géogrille confinait les agrégats granulaires conduisant à une augmentation de la raideur latérale et de la
rigidité de la couche de base stabilisée. Pour vérifier que ces résultats sont applicables à différents types de sols de fondation et à
d’autres matériaux granulaires, d'autres essais in-situ à grande échelle ont été réalisés à Salt Lake City, Utah, Etats-Unis. Un total de
quatre capteurs de pression ont été installés dans les sections d'essai, espacés de 2,6 et de 2,9 mètres de l'axe et décalés de 3 mètres
parallèlement à la direction de déplacement. Un matériau non traité a été utilisé comme couche de base dans cette étude. Les résultats
montrent que les pressions horizontales dans le sol de fondation créées par les deux conditions de chargements statique et dynamique
ont été significativement réduites par l'utilisation de la géogrille, alors qu'une augmentation de 80% des pressions horizontales a été
mesurée pour la section de contrôle après la pose de matériaux d'agrégats, par rapport à la section stabilisée. Cet article présente les
résultats et l'analyse de ces études in-situ. Les résultats confirment que la géogrille favorise le confinement et l'interaction des
agrégats, conduisant à améliorer la performance structurelle de la couche granulaire non revêtue.
KEYWORDS: Field trafficking performance, Triaxial geogrid, Lateral stress, and Resilient modulus.
1 INTRODUCTION.
In cases where a gravel surfaced road is required over subgrade
conditions that are unable to adequately support the traffic loads,
geogrids are commonly used to stabilize the aggregate base
course and improve pavement performance by decreasing the
load distributed to the subgrade. The aggregate that is directly
above the geogrid is laterally confined and the result of this
enhanced confinement leads to an increase in the resilient
modulus of aggregate adjacent to the geogrid. As a result, the
stabilised aggregate spreads surface loads over a wider area of
subgrade. In general, an equivalent stabilised road section
thickness yields an increased allowable traffic load compared to
an unstabilised road section.
Geogrids have been used successfully to improve the
performance and increase the design life of unpaved roads since
the 1970’s. Nonwoven geotextiles have been efficient in
applications that require the separation of aggregate layers from
the underlying subgrade soil.
Throughout the history of geosynthetics, monitored full-
scale field studies have been extensively utilized to study the
performance of geogrid stabilised sections. Although more
sophisticated and precise methods, (i.e., numerical modeling
and laboratory test models) can be utilized to study specific
variables and/or to optimize a geosynthetic, a basic field study
remains as one of the most effective means of providing a
definitive proof of performance.
Full scale research has provided guidance, basic criteria and
information for the use of geogrids in roadway design (Tingle
and Webster 2003). Subgrade bearing capacity factors of the
unstabilised and stabilised sections were determined using
empirical data from full scale testing performed by the
Engineering Research and Development Center (ERDC). The
