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The problematic

Dimensioning and solicitations specific to these rings


Issues and consequences

The management of roundabouts, being traffic nodes by definition, remains a complex element.

The specific constraints that are applied, the difficulty of maintenance that they cause as well as the phasing of the often complex work to be carried out are all elements to be taken into account in a reinforcement project.


Specific requests in operation

High traffic density and circular geometry are at the heart of the specificity of roundabouts.

Present on pavements sometimes sized for the largest classes of traffic, these strategic locations are both acceleration/braking zones and cornering zones, which makes them particularly difficult to maintain.


Due to their geometry, associated with the speed practiced on these rings, the roundabouts are subject to their own constraints.

  • Shear forces

The access roads, braking and acceleration zones, cause load transfers between axles, while requiring high grip constraints.

On the annular roadway of roundabouts, the increased stresses are caused by the rotational forces of the vehicle axles on the roadway. This phenomenon results in a significant increase in tangential shear stresses.

To this are added the tangential forces resulting from centrifugal force, causing fatigue phenomena within the bituminous structure.

  • Structural constraints

The speeds used in roundabouts are lower than in rectilinear traffic. Consequently, the load application time is proportionally longer than in straight road sections.

In addition, the traffic extremely canalized by particular conditions linked to the geometry of the pavement also causes an increase in constraints.

Therefore, the effect of the centrifugal force resulting directly from the turn unbalances the load distribution between the wheels on the same axle, causing the wheels outside the turn to overload (+20 to 60%).


Tangential forces: Source of fatigue

Tangential forces due to mass transfers as well as the resultant centrifugal force exerted on vehicles in bends, applied repeatedly, cause the fatigue failure of the asphalt sizing layers (emulsions).

This phenomenon is quickly synonymous with the uncoupling of asphalt layers, leaving behind structural failures.


Outre le cisaillement dû au pivot quasi-statique des roues de véhicules lourds, des efforts tangentiels résultant de la force centrifuge sollicitent également la chaussée de façon répétitive.

Ce cas de charge se retrouve essentiellement au sein des giratoires et virages à faible rayon. Les poids lourds - principaux acteurs des dégradations d'usure routière - sont particulièrement soumis à ces efforts, par leur poids et géométrie associée.
Leur hauteur, ainsi que la hauteur à laquelle est placée la charge qu'ils contiennent (outre leur poids à vide), augmente considérablement les transferts de masse sur les roues extérieures.

Ces efforts, appliqués de façon répétée aux passages de chaque poids lourd sur une chaussée de ce type, provoquent le décollement des couches d'enrobés bitumineux par fatigue, occasionnant orniérage et / ou arrachements tout en laissant place aux fissurations associées.


Need to maintain traffic during the work

Roundabouts require special operating conditions linked to the duration of the work.

The maintenance of traffic (often being an input to the repair of these rings) then requires an optimized and perfectly controlled pace in order to limit the discomfort caused.


When a roundabout needs to be cleaned up, the absence of a deviation possibility can lead to traffic being maintained during the work.

As a result, it constitutes a work site divided into phases and completed in a reduced time in order to minimize inconvenience to users.

This imposed phasing constitutes a significant risk of discontinuity in the structure and is therefore a source of additional tensions (differential settling, opening of the recovery joints, etc.).

The high traffic density within these structures is a point to be anticipated in the management of a roundabout reinforcement operation: minimising the duration of the works remains an essential point for the smooth running of a construction site in these busy areas.


TEXUM expertise

By integrating all the parameters specific to the rehabilitation (or creation) of a roundabout, from the technical specificities to those of implementation, Texum has developed a reinforcement solution specially designed for this type of pavement.

This solution is composed of a SAMI membrane reinforced with a quadriaxial carbon fibre geogrid.


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