JG Afrika took swift action on behalf of the Bakwena Platinum Corridor Concessionaire to repair the damaged Groot Marico River Bridge on the N1/N4 to prevent further damage and provided road users with a more convenient alternative to a 36 km detour while repairs were being undertaken.
JG Afrika is contracted by Bakwena to undertake regular inspections and oversee the maintenance of the major structures along the route. The Groot Marico River Bridge is among the largest of the 280 structures along the highway.
The firm first noted the crack in one of the bridge’s piers in 2015 during the routine bridge inspections, and noted on the Bridge Management System, which JG Afrika uses to monitor the state of the structures and prioritise repairs on behalf of the Bakwena Platinum Corridor Concessionaire.
Located in the North West province, the 80 m-long bridge is 7 m high and comprises six spans and five piers. The first half was built in the 1970s and the second is tied to the original structure and was constructed in 2002.
After extreme flooding in the North West province in early January 2017, the crack in the bridge pier widened. This resulted in the rotation of the pier and the settling of the deck structure.
“The settlement was on the older side of the structure. We immediately closed this section and implemented a stop-and-go system to redirect the vehicle traffic to the newer portion of the bridge. This provided a safe short-term solution until we completed our assessments of the settlement to determine the actions that were required to repair the structure,” says Emma Day, a JG Afrika associate and highway engineer.
Assessments, done by JG Afrika’s bridge engineer Mr Kobus Burger, revealed that the failure was as a result of the erosion of the founding material below the old bridge’s spread footings.
The initial design entailed installing piles at the four corners of the failed pier, and a concrete beam with a lip would be cast between the piles to support the pillar. However, the engineering team had to quickly come up with an alternative solution when the damaged pier rotated further when piling commenced during the repair operations. They decided to dowel into the existing pier and to then cast it into the concrete beam.
Designed in only a week, this solution also proved to be a more effective means of undertaking the repairs by doing away with the need to excavate below the pier to construct the lip on the concrete beam.
The river was diverted by a large berm, by the main contractor G4 Civils before the installation of the propping and staging to support the bridge during the repairs.
Stefanutti Stocks Geotechnical commenced piling once the bridge deck had been supported. Their scope of work also included the construction of piled protection structures in front of the piers on either side of the failed pier to prevent the possible failure of the other piers.
After their installation, Civilcon started constructing the concrete beams to join the piles and support the pier.
A rapid high strength concrete was used to further accelerate the works programme, with this 40 MPa concrete mix design achieving a desired strength in only seven days.
With the structure now stabilised, MBR jacked the bridge up by 100 mm to its original height. The bridge deck was then supported on steel shims of varying heights to accommodate the angle of the pier. This phase was followed by the repair of the crack and the reinstatement of the river bed to complete the repair works.