Replacement Piles for the Houphouet-Boigny Bridge, Cote D'ivoire-Paper

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The Houphouët-Boigny Bridge in Abidjan is a vital road and rail link between Côte d’Ivoire’s interior and its port. After decades of heavy traffic, corrosion, ground movement and other damage, the bridge required major repairs, including replacement of foundations whose condition could not be confirmed. Traffic on the bridge and in the lagoon had to remain operational throughout construction.<br /><br />New piles had to be installed beside the existing foundations and could not extend below their toes, to avoid undermining the working bridge. Soft silts and loose sands also meant the piles needed to transfer most of their loads into deeper, competent sand through end bearing. Instead of increasing pile size or number, the project team improved the ground beneath each pile: four jet-grouted columns were installed below each pile toe. Preliminary load tests showed that this treatment increased ground stiffness and reduced settlement.<br /><br />Parallel seismic surveys confirmed the existing pile depths before construction. A total of 56 replacement piles, up to 68 metres deep, were bored from marine platforms. After the piles were built, 224 jet-grouted columns were formed beneath their toes. Coring and strength tests verified the grout columns, while sonic logging checked pile integrity.<br /><br />Careful planning was essential to manage strong lagoon currents, marine traffic and the risk of affecting the existing foundations. By tailoring the ground to the required pile capacity, the design avoided larger or more numerous piles, reducing concrete, steel, spoil handling and associated transport and disposal.

Keywords

Houphouët-Boigny Bridge

Abidjan

Côte d’Ivoire

bridge rehabilitation

replacement piles

jet grouting

foundation repair

marine construction

pile load testing

ground improvement