Professional consulting engineering company SMEC South Africa has completed the two-phase R55 project, which entailed upgrading a 6-m-wide single carriageway to a dual carriageway – comprising four lanes, two each in the opposite direction – five bridges across the Hennops river, which passes through Centurion, near Pretoria, and installing new streetlighting for both phases.

The first phase of the project, the 6 km stretch of road from the N14 to the K103 (Wierda road), was completed in November 2009 and cost about R268-million.

The second phase was completed at the end of 2012 and cost about R228-million. This recently completed phase is from the K103 (Wierda road) to the P39/1. The R55 is an important economic and public transport link between Pretoria and Johannesburg.

“The second phase of the project, which officially opened on November 22, 2012, runs from Weirda road to the P39/1 and is about 4 km long. We began working on the second phase in November 2010,” says Vela VKE’s technical director in the Pretoria Implemen- tation Division, Tshepo Matshego.

New technology was used during the construction of the piles of the bridges in both carriageways. The area where construction took place is underlain by dolomitic soils, which are prone to sinkholes, and the bridges are founded on piles ranging between 8 m and 25 m in depth. These factors resulted in the contractor proposing a new method – the Odex piling method.

Matshego explains: “The Odex piling method of construction is not entirely different from the normal procedure. This method uses pressurised air and Rotafoam to bring the excavated debris to the surface. One challenge of this method was that, once we hit a pocket of air underground (as can be expected in dolomitic areas), the drilling machinery jammed. This meant the drilling bit had to be pulled out and resulted in time delays. However, the contractor, Esorfranki Civils, made up time by fast-tracking the construction of the superstructure.”

During the period December 2010 to March 2011, when the second phase started, there were heavy rains in the area that affected the start of piling owing to the overflowing of the Hennops river. This was a major challenge as the accommodation of traffic was such that the bridge on the new carriageway had to be completed first so that traffic could be moved there while the existing carriageway was being rebuilt. The bridges were then on the critical path and the rains set the project back by two months.

“The road is open for use and has boosted growth in the area, with housing and industrial developments along the route. The upgrading of the road has come at an appropriate time,” concludes Matshego.