Detail Design of two "deck-on-piles" bridges, Nigeria

Lagos’ road infrastructure is struggling to stay ahead of population growth which has led to extensive traffic congestion. Lagos State Government appointed our client, Hitech Construction Company, to design and construct road upgrades in the Isheri Area of Lagos to alleviate the congestion in that region. One of the project roads traverses two wide marshes. Hitech appointed Aurecon to design the two bridge structures, which are 700m and 200m long respectively, to cross the marshes.

Located in a coastal region, the project site posed many construction constraints and challenges, including poor drainage and founding materials and the lack of materials for the construction of fills.

Aurecon conducted a thorough investigation into a full range of engineering solutions for the two bridges. Due to the environmental conditions of the natural marshes, it was necessary to provide a straightforward and practical solution which made use of repeated design elements. In addition, the design needed to be easily enacted within a short construction period, even with a limited availability of equipment.

After an intensive foundation investigation, it was decided that the use of friction piles offered the best technical solution (some 1 000 were used in total). These “deck-on-piles” bridges, made up of in-situ cast concrete beams with precast concrete slabs forming the 40 long deck spans, would be perfectly suited to overcoming the lack of good foundation layers and rock bed.

To facilitate fast construction and reduce cost, the in-situ beams were constructed on top of a temporary berm to negate the need for support and formwork. The berm will later be removed after the completion of the bridge to prevent damming and allow for free drainage of the marsh.

Ultimately, Aurecon delivered a bridge design which included an appropriate configuration which would affect minimal environmental impact.

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