Challenging road construction in Benin 

A major provincial road built on a particularly difficult base course is to be reconditioned in the West African country of Benin.
On the face of it, it sounds like an easy job for a professional road builder: 42 kilometres of existing road in Benin is to be re-surfaced. But the challenges are greater than they seem on the route between the provincial towns of Pobé and Kétou.

"It is a road builder's nightmare. Sections of the road are built on extremely poor material, so-called 'expansive soil'. The soil lacks any bearing capacity when it is wet, with the result that we cannot build directly on it," says Project Manager Andrew Inman, COWI.

The road has crumbled away

The project is part of Danida's road sector program in Benin. The road links up with the main road between Togo and Nigeria, and links the northern part of the country with the capital Porto Novo on the coast.

The current surface of the road dates back to 1982. The project road is in a very poor condition and in places the original asphalt has completely disappeared. COWI is responsible for the detailed design, the preparation of tender documents for an international tender, and the supervision of construction works.

Fibre cloth in the pavement construction

The fact that expansive soils are present has to be taken into consideration in the pavement design. As yet it has not been decided exactly which solution will be employed, but Andrew Inman mentions the possibility of using a geo-textile, e.g. a fibre cloth in the construction of the new pavement. A geo-textile laid on top of the sub-soils would keep the layer separate and control the differential settlement.

As part of the project, funds will also be made available for additional local infrastructure and other development projects designated by the local population, and training in road safety will be given in schools and local communities.

Benin is far from the only country in Africa where COWI builds roads. At present, COWI is also providing consultancy services for road projects in Tanzania, Ghana, Uganda and Ethiopia. 

By: Janne Toft Jensen, jaje@cowi.com
Published: 05.05.2004


Expansive soils  
Certain clays will expand (increase in volume) as it absorbs water and will shrink (lessen in volume) as water is drawn away. These clays are determined to be "expansive soils". Expansive soils are particularly prevalent in the Tropics.

These types of soil often cause major damage to the infrastructure, in countries whose climates include annual dry and rainy seasons.