JG Afrika helps SANRAL drive another strategic road upgrade

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JG Afrika helps SANRAL drive another strategic road upgrade

JG Afrika, a leading engineering and environmental consultancy, is overseeing the upgrade of a 48 km section of the N2 highway between Caledon and Riviersonderend in the Western Cape.

The road serves as a vital link between the Eastern Cape and KwaZulu-Natal, and about 3 500 motor vehicles and 500 trucks use this economic and tourist route every day to travel between Cape Town and the many cities along the south and eastern coastlines.

Moreover, the project is being used as a fertile training ground for many local small, medium and micro enterprises (SMMEs) in line with the South African National Road Agency Limited’s (SANRAL) “Fourteen Point Plan.” It emphasises the critical role that road construction projects can play in assisting government grow a vibrant emerging contracting industry in the country.

This is just one of a number of projects in the region and along the N2 that SANRAL has prioritised to serve a larger socio-economic role by developing many black-empowered emerging contractors and creating construction-related employment opportunities for members of poor communities.

As many as 11 SMMEs are being trained by the main contractor, Group Five, which mobilised to site to commence working on the 36 month construction project in September 2017.

As part of their training, they have been tasked with the less onerous aspects of the work scope. This includes removing and erecting fencing and guardrails; providing security and traffic-control services; undertaking clearing and grubbing operations; as well as constructing the side-drains.

At the same time, the project has also created jobs for more than 100 people, the vast majority of whom are from communities in the area.

Duncan Murphy, a technical director with JG Afrika, has been involved in the project since December 2014 when the firm was initially appointed to undertake the design, and he has also been leading the team of engineers overseeing the construction programme.

Murphy says that the lion’s share of the work scope entails widening the road, which was built between 1978 and 1983, as well as upgrading its intersections to better accommodate the increase in traffic over the years and raise safety levels for road users.

“The road mainly comprised a single carriageway with surfaced lanes and shoulders. Its surface width varied between 11,5 m and 17,5 m, except for the first 1,12 km, which consisted of four lanes with a raised median island in areas. Once we have completed the project, it will have a minimum surface width of 13,4 m, including two 3,7 m-wide lanes and three metre-wide shoulders, in areas. Where there are existing climbing lanes, the road is being widened to allow for 3,7 m-wide passing and 3,7 m-wide climbing lanes, as well as a 1,5 m-wide surfaced shoulder. Some of the existing climbing lanes are being extended and we are constructing new climbing lanes,” he says.

Five new climbing lanes are being built and five existing climbing lanes widened, lengthened, or a combination of both when travelling from Caledon towards Riviersonderend.

Meanwhile, four new climbing lanes and five existing climbing lanes are being widened, lengthened, or a combination of both in the opposite direction.

There are 26 road junctions and 106 farm accesses located along the route, and eight of the road intersection being improved. This includes right-turn lanes that are being built at two intersections, as well as acceleration lanes that are being added to the eastbound lanes at a further two junctions.

At two other intersections, a left-turn lane is being constructed on both approaches and the existing geometry upgraded. A passing lane has been included on the westbound lane and an additional right-turning lane built on the same side, while rumble strips will also be installed on the approaches to the highway.

Moreover, a right-hand lane has been included on the westbound lane at a further two intersections.

A 50 mm medium-continuously graded asphalt overlay is being placed on the first 1,4 km duelled section of the road using a conventional 50/70 penetration grade bitumen binder.

The pavement layers comprise a 200 mm-thick G4 crushed stone base compacted to 100% of maximum dry density and a 200 mm-thick G5 crushed stone sub-base compacted to 97% of maximum dry density. This is in addition to a 150 mm-thick G7 upper-selected layer compacted to 95% of maximum dry density; a 150 mm-thick G9 lower selected layer compacted to 93% of maximum dry density and minimum G10 quality material to a pavement depth of 1 000 mm compacted to 93% of maximum dry density.

The bulk of the material for the layerworks is being sourced from a commercial quarry in the immediate vicinity, and cost-savings in materials has been realised by using about 30 000 mᵌ of fill material from the approximately 80 000 mᵌ of cuttings undertaken on the project.

The existing road is also being repaired, based on the findings of a visual survey undertaken by JG Afrika in January 2015.

Murphy says that the distressed pavement layers of the existing carriageway are being patched using hot-mix asphalt.

An appropriate micro-surfacing, slurry or asphalt surfacing is being used to shape and correct undulating areas, while ruts exceeding depths of 15 mm are being filled with a 40 mm-thick “mill-and-fill”.

A 10 mm single-seal armour layer is being applied on the completed base layer of the widened carriageway areas and a texture slurry over the entire carriageway before the final surfacing seal.

The entire carriageway, including the existing and widened areas, is being sealed, or resealed using a 20 mm and double seven millimetre seal.

He says the work scope also includes the widening of Droogas River Bridge and Maandagsout River Bridge, as well as the lengthening of 14 major culverts along the route.

Droogas River Bridge comprises two-spans of simply-supported reinforced-concrete deck, supported by a wall-type pier and closed-faced abutments positioned at 90° skew angle to the road centre line.

It is being widened by two simply-supported spans with about a 3,5 m clearance above the access road and 4,5m above the river bed to create a 1,95 m solid reinforced-concrete deck.

The existing barriers will be replaced with cast in-situ F-Shape barriers, while the foundations for the abutments, wing-wall extensions and central pier comprise pad footings on the hard shale, and they are identical to the structure’s existing foundations.

Maandagsout River Bridge comprises a three span simply supported 610 mm-thick reinforced concrete deck with wall-type piers and closed-faced abutments positioned at a 60° skew angle to the road centreline.

The new deck, which has a minimum depth of 550 mm, is being constructed with concrete and is similar in appearance to the existing structure, while the existing barriers are being replaced with cast in-situ F-Shape concrete elements.

Its existing piers and abutment walls are supported by caissons. Due to the close proximity of the works to the existing structure, pilings support the widened section’s piers and abutments, which have also been founded on hard shale.

A total of 94 of the 117 minor culverts along this section of the N2 are being lengthened, while new concrete-lined drains, down chutes, catch pits, cut-off drains, toe drains and erosion protection are being constructed along the widened sections.

Murphy is satisfied with the progress that has been made thus far, and attributes this success to a design that is workable and correct right from the outset, and complemented by the skills and capabilities of the engineering team deployed to this construction site.

Importantly, members of his team have been able to think on their feet to overcome unforeseen challenges that arise on typical brownfields road projects. This includes the delays in the relocation of undetected services along the route, as well as the clay material that was encountered within the immediate vicinity of Caledon.

Moreover, the professional team had to abide by a very strict road-closure regiment, considering the high vehicle traffic.

For road widening, construction sections are limited to 12 km with a maximum number of two construction sections at any one time. In addition, a minimum distance of 12 km between each construction section has to be maintained.

A single 12 km carriageway section is widened to the specified cross-section and width and two-way traffic is accommodated during the execution of the widening works at all times.

These are only permitted on one side of the carriageway at any given time. Existing road markings are removed and replaced with temporary markings to indicate the amended lane configuration during completion of the widening operations.

Once the widening works have been completed up to base level and the 10 mm Cape Seal armour layer has been applied to widened areas, the remaining preparatory works are completed up to the road’s centre/alignment line. This preparatory work accommodates traffic in half-widths using a “Stop/Go” system during the day and ensuring two-way traffic at night.

Work on the opposite side of the 12 km long carriageway section starts once the adjacent preparatory work has been completed.

The widening works and subsequent preparatory works on the opposite side are completed in the same manner and the specified final seal is applied once all of the preparatory works has cured.

Meanwhile, the application of the final seal over this 12 km road section is undertaken in one continuous operation in half-widths and two-way traffic is accommodated on the other half of the carriageway where sealing is not being done. This work is planned in such a way that the longitudinal construction joint falls on the road centreline or alignment line where the equipment has been established. These longitudinal joints are in line with the specified lane markings.

Traffic is only allowed on the completed seal and the construction of the final-seal surfacing over the 12 km road section is completed swiftly to minimise the disruptions to traffic.

A maximum of four Stop/Go setups are permitted at any one time and with a minimum distance of three kilometres between each setup.

Murphy concludes that he is proud to be involved in another SANRAL project that has again highlighted the larger role that road construction projects play in society by also providing ample training and employment opportunities for disadvantaged communities.

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