2863
Cavity remediation for pylon foundation of the Transrhumel Viaduct in Constantine
Résolution des problèmes de cavité sous les fondations du Viaduc Trans-Rhumel de Constantine
Steenfelt J.S., Schunk M.
COWI A/S, Denmark
ABSTRACT: The geology of Constantine, Algeria is highly influenced by previous seismic activities and the erosional feature by the
river Rhumel. The Transrhumel Viaduct is a new river crossing featuring a 749 m long cable stayed bridge with a main span of 259 m
and 80 m clearance. The soil/rock deposits are dominated by Marls of different strength underlain by Marlstone and very competent
Limestone. However, exploratory boreholes for the foundation piles of Pylon P4 indicated the presence of possible cavities of up to 1
m high within the Limestone at the base of the upper weathered zone. To save 15 m of time consuming drilling of the 14 Ø2 m foun-
dation piles into competent Limestone it was decided to end the foundation piles above the possible cavity feature in the Marlstone.
The paper describes the innovative remedial measures carried out to safeguard the capacity of the individual foundation piles and en-
sure acceptable individual and overall displacements. The cavity feature was pressure grouted and transfer of axial load across the
cavity into Limestone was facilitated by insertion of grouted steel reinforcement assemblies. The success of the remedial measures
was proven by carrying out an O-cell load test on the pile positioned over the maximum recorded depth of the cavity.
RÉSUMÉ : Les conditions géologiques de la ville de Constantine en Algérie sont pour une grande part le résultat d’évènements sis-
miques passés et de l’érosion de l’oued Rhumel. Le viaduc Trans-Rhumel est un nouvel ouvrage qui traverse le court d’eau compre-
nant un pont à hauban de 749 m avec une travée principale de 259 m placée à une hauteur de 80 m. Les sols de fondation sont majori-
tairement composés de marne de compétence variable supportée par des roches marno-calcaire et roches calcaires très compétentes.
Les sondages par forages effectués au droit du pylône P4 ont cependant révélé la présence de cavités d’une hauteur jusqu’à 1 m dans
le calcaire à la base de la zone érodée supérieure. Afin d’économiser 15 m de forage onéreux pour les 14 pieux de 2 m de diamètre
dans la roche calcaire, il a été décidé de stopper les pieux de fondation au-dessus de la zone de présence probable des cavités des ro-
ches marneuses. Cet article décrit les mesure innovantes mises en place pour assurer la capacité portante de chaque pieu de fondation
et garantir des déplacements globaux et individuels acceptables. Un coulis de ciment a été injecté dans la cavité et le transfert des ef-
forts axiaux au travers de la cavité fut assuré par l’insertion d’assemblages d’armatures placées dans le ciment. Le succès de cette mé-
thode a été démontré en exécutant des essais de charges O-cell sur le pieu fiché à la hauteur maximale de la cavité.
KEYWORDS: natural hazards, cavity, bored piles, pile load test, pressure grouting, Marls, Limestone.
1 BRIEF PROJECT DESCRIPTION
The Constantine Viaduct (Figure 1) is a new bridge, crossing
the River Rhumel in Constantine, Algeria. Constantine is situ-
ated on a plateau at 640 metres above sea level. The city is
framed by a deep ravine and has a dramatic appearance with a
number of bridges and a viaduct crossing the ravine.
Figure 1. Artist's impression of completed cable stayed bridge (Pylon P4
to the left).
The main bridge features a cable-stayed bridge as well as access
and ramp bridges. The project includes very extensive road
works of approximately 10 km, with 13 over and underpasses,
1 km of up to 45 m deep steep cuts stabilised with ground an-
chors and soil nails, 4 km retaining walls of which 1 km em-
bedded retaining walls were stabilised with ground anchors (up
to 32 m retained height).
The total length of the bridge between the main abutments is
749 m with an 80 m clearance over the river bed.
The Owner is Direction des Travaux Publics de la Wilaya de
Constantine – DTP and the contractor is Andrade Gutierrez -
AG from Brazil with COWI A/S Denmark as designer.
2 GEOLOGY WITH FOCUS ON PYLON P4
The geology of the site is highly influenced by previous seismic
activities (medium severity) and the erosional feature by the
River Rhumel.
The soil/rock deposits are dominated by Marls of different
strength underlain by Marlstone and very competent Limestone.
At the original position of Pylon P4 a very dramatic ancient
fault was discovered where the Limestone surface dips near ver-
tically and hence the Pylon was moved 14 m to the north, thus
enabling the foundation to be completely based on bored piles
with the toe well into the Limestone formation (Figure 2).
