Civil Engineering December 2021 | Vol 29 No 11

Civil Engineering December 2021 29 W ith Section 6 of National Route N6 between Rouxville and Smithfield in the eastern Free State having reached the end of its service life, SANRAL appointed Zutari (previously Aurecon) to undertake the design and construction supervision of this 40 km section of road. The project purpose was to ensure the upgraded route would meet all current and future transportation and safety needs for the design horizon. Key aspects of the project were: Q Q Extensive road pavement strength- ening with an improved vertical geometry and road cross-section Q Q The addition of several passing lane road sections Q Q Rehabilitation of all large drainage structures Q Q Widening of the multispan Caledon River Bridge Q Q Replacing the bridge over the Eldorado River Q Q Upgrading all surface and subsurface drainage features Q Q Upgrading all road furniture Q Q Improving pedestrian safety in Rouxville and Smithfield Q Q Formalisation of walkways, parking layout and roadway through Rouxville Q Q Improvement of pedestrian infrastruc- ture within Roleleathunya. Investigations and design work started in 2014, construction commenced in June 2017 and was completed within the extended project time by December 2020. TWO VERY DIFFERENT BRIDGES Bridge works were fast tracked to complete footings and extensive piling during the dry season. The Caledon River Bridge was wid- ened on both sides using pre-stressed beams manufactured off-site. The works, involving widening of the piers and abutments proved quite challenging due to unpredictable flood levels and the asymmetrical dimensions of the existing structure, which required adjustments to various concrete elements as the works unfolded. All such adjustments were addressed in a timely manner, avoiding any significant adverse impact on works progress or costs. While the Caledon Bridge works could progress under traffic, the Eldorado River Bridge had to be demolished and replaced, resulting in the need for a cost-efficient temporary bypass with suitable drainage provision. This was achieved by balancing the number of culvert openings with the formation fill height, as well as adequate side-slope protection in the event of any overtopping by flood waters. In fact, over- topping occurred twice but the temporary measures were adequately effective. ROADWORKS APPROACH AND CHALLENGES The roadworks required extensive mass earthworks and improvements to roadbed conditions. This was exacerbated by the increased moisture level of the in situ silty-sand soils during a very wet rainy season in 2017/2018, which necessitated additional works to repair and strengthen roadbed conditions. A conventional 450 mm pioneer layer that incorporated the lower pavement layer was the most cost- and time-efficient solution. Some minor vertical geometry adjustments were also implemented where roadbed under- cutting could be cost-effectively reduced. Improvements to the vertical road geometry required lowering of several ex- isting crests. The in-situ materials consisted mainly of mud rock and required extensive blasting operations. The depth of several cuttings impacted on the available road re- serve width, which was solved by expropria- tion in extreme cases and/or the adjustment of side slopes through use of gabion walls. Virtually all pavement layers were re- placed with new layers and only limited in situ layers constructed where conditions allowed. CONCLUSION Although the rehabilitation works on the N6 route were outwardly a conventional road construction project, the project team faced many unique challenges. Their unwavering and committed team effort ultimately ensured a successful project outcome that met all client requirements and expectations. The exemplary concern given to generating benefits for local businesses, improving infrastructure, and addressing road user safety will certainly go a long way towards uplifting communities in the area and offering road users a much im- proved and safer traveling experience.  SANRAL SA I CE 2021 Nat i onal Awards Category: Techn i cal Excellence FINALIST Technical Excellence category (Sponsored by Maccaferri SA) KEY PLAYERS Client: SANRAL Consultant: Zutari Contractor: WBHO Rehabilitation of National Route N6 between Rouxville and Smithfield The completed Caledon Bridge Replacing Eldorado Bridge to improve hydraulic capacity