Cover of Innovative Bridge Raising for Flood Immunity
Innovative Bridge Raising for Flood Immunity
  • Publication no: ABC2017-054-17
  • Published: 21 April 2017

This article describes the innovative raising of an existing 201 m long, six span bridge by 2.3 m for flood immunity.

The existing National Road 2 (N2) near Colchester, in the Eastern Cape province of South Africa, was in a poor state with signs of pavement failure and general poor riding quality.

The South African National Road Agency Limited (SANRAL) appointed Aurecon in a joint venture with Semenya Furumele Transportation Engineers, for the upgrading of this portion of road. Traffic studies showed that a dual carriageway highway is required and this meant that the existing carriageway had to be rehabilitated and a new carriageway constructed.

The N2 crosses the Sundays River near Colchester by means of a 201 m long, six span bridge. The catchment area of the Sundays River Bridge is very challenging and includes two sizable dams. A very sophisticated hydrological model showed that the existing bridge was not able to accommodate the design flood with the required freeboard. After a number of options were considered, it was decided to raise the existing deck level by 2.3 m. The raising of bridge decks are normally required to provide additional clearance for overpass bridges and seldom exceeds 1 m. Raising of the existing deck over water by approximately 2.3 m required careful planning and an innovative approach.

The article will focus on the design and particularly on the innovative construction techniques employed during the raising of the bridge. The end result provided an extremely cost effective solution while the intervention will be all but invisible to the untrained eye.