Construction of the Msikaba Bridge near Lusikisiki in the Eastern Cape – which started in earnest in late 2019 – continues to make good progress. The bridge’s four huge anchor blocks are now nearing completion, over 50 % of the concrete for the bridge’s two 127 m high pylons has been poured and the complex deck construction phase of the project is about to start.
On the safety front, the project has a superb record, with 3 million LTI-free hours being notched up on 21 October 2022. This is a major achievement for a technically demanding project which has a large workforce (more than 500 people currently), who have mainly been recruited locally and who, for the most part, had no formal sector work experience of any kind prior to recruitment.
The Msikaba Bridge, which forms part of the South African National Roads Agency Limited’s (SANRAL) N2 Wild Coast project, is being constructed by the CME JV, a partnership between Concor and MECSA, both 100% black owned Grade 9CE South African construction companies. Along with the still-to-be-built Mtentu Bridge, Msikaba – which will span the spectacular 198-m deep Msikaba River gorge – will drastically cut travel times for vehicles travelling between the Eastern Cape and KZN with the time saving being up to three hours in the case of heavy freight vehicles.
Commenting on the Msikaba Project, Concor’s Laurence Savage, who is Project Director, says “the cable-stayed bridge, which will contain 48 500 m3 of concrete and 2 900 tonnes of structural steel, is probably the most complex structure of its type ever to be built in South Africa and probably in Africa, and particularly when you understand the remoteness and logistical challenges faced in an environment where two weather systems confluence resulting in substantial wind challenges.”
“Msikaba will be a truly iconic structure,” he says. “At 580 m in length, it will the longest cable-stayed bridge – in terms of main span – in Africa and it will have the second longest main span of any bridge on the continent. At 192 m above the floor of the gorge, it will also rank as one of the highest bridges in Africa, only exceeded by the Bloukrans Bridge at 216 m and, once it is completed, Mtentu at 223 m.”
Cable-stayed designs are well-known for making aesthetically pleasing bridge structures and Msikaba is no exception. As Savage says, “The bridge, which will accommodate a dual two-lane carriageway, has an extremely slender design which will make it very pleasing on the eye. Moreover, it does not disturb in any way the natural environment of the gorge.”
The bridge is being built from both the north and south banks of the gorge and comprises two identical ‘halves’, each spanning 290 m, which will meet mid-point over the gorge. Each half is supported by 17 pairs of cables attached to 127 m high inverted Y-shaped concrete pylons, one on each side of the gorge, which are essentially tapered circular shafts that straddle the roadway by means of inclined legs. The pylons are back-stayed into the anchor blocks by 34 pairs of cables – 17 for each half – which are positioned 130 m behind each pylon.
Commenting on progress on the project thus far, Savage says that an important milestone was reached in April 2022 when the south pylon legs were hydraulically jacked apart. These two legs make up the first 20 m of the pylon and were built without any lateral support as free cantilevers. The jacking apart of the legs countered the bending moment at the bases of the cantilever structure placing them into a ‘straight’ position before they are joined together.
With both pylon legs and the bifurcation section above the legs now completed, the focus is now on the construction of the pylon spires and the first lift on the south spire started in November 2022. The JV is utilising a custom-designed 15 m high climbing formwork system for spire construction. This provides four levels for concrete, fixing, curing and cleaning. It also accommodates the complex geometry of the spires, which start with a diameter of 6 m but taper to 4.5 m diameter at full height. The pylons are both expected to be fully complete in September 2023.
Discussing the anchor blocks, Savage describes these as the “unsung heroes of the structure”. Each block has a length of 49 m, a width of 10 m at the base (narrowing to 4 m on the spine of the structure), a depth of 17.2 m, and a mass of 21 500 tons.
“These blocks are critical parts of the bridge and yet are not very prominent as they are contained in huge excavations – of 100 MPa rock. These anchor blocks were one of the first elements that we started constructing, recognising the volume of work required to meet programme, ,” he says. “The excavations were achieved by means of restricted blasting in 2 m stages and for each stage lateral support was installed to the excavation walls using rock anchor rods, drape mesh and shotcrete to ensure that the excavations remained safe during construction.”
He adds that on completion of the bulk excavations intensive dental excavation and finishing work was required. This involved the hand excavation, and the cleaning of crevices before the placing of mass concrete as a blinding layer for the structural foundations. The dental cleaning of the crevices and concrete blinding ensured stability and security of the integrity of the foundations.
All four anchor blocks will be fully complete in Q1-2023, opening the way to another critical part of the project – the construction of the steel-concrete composite deck over the gorge. This is an exercise which – among many other challenges – has to consider the significant wind conditions that occur at the site.
The first 24 m of the deck on either side of the gorge is a reinforced concrete ladder deck that is cast into the first steel deck segment, known as deck segment zero, DS0. Because of crane access restrictions, DS0 will be slid laterally into place before reinforcement is installed and concreted. The remaining segments, DS1 through to DS17 on either side, will be installed using the free cantilevering method, with each segment being installed in sequence.
To place the decks in position, two gantries, specially designed and manufactured by Freyssinet, the sub-contractor for the cable-stay system, will be used. These are large 160-ton assemblies, each 30 by 15 m by 7 m high, which are able to launch the deck segments – which have an average weight of 84 tonnes – over the gorge, rotate by 90 degrees, lower and align them with the previous segments.
Once a segment is in position, the next steps would be to weld the segment to the previously placed segment; installing the stay cables and applying initial tensioning; installing formwork and reinforcement; casting the 250 mm thick concrete deck slabs; and final tensioning of the cables. The launch gantry is then positioned for the launch of the next segment.
Underdeck gantries on either side are required to facilitate welding, the installation of deck formwork and the movement of materials. They will outlast the construction phase and be used for routine maintenance inspections and maintenance once the bridge is in operation.
“The gantries, which have come from Europe, are expected on site shortly as are the first steel deck elements, which we are sourcing locally,” says Savage. “We will start launching the deck segments in early 2023 at a rate of two segments (one from either side) every two to three weeks, with this speeding up to around a segment every second week from either side by Easter. We are expecting to substantially complete the deck in 2023 with closure at the mid-point being achieved in Q2-2024. Commissioning of the bridge will follow later in 2024.”
The scope of the CME JV’s work at Msikaba includes not just the bridge itself but also what are known as four tributary structures that lie outside the bridge construction site. These are concrete structures bridging tributaries of the Msikaba River. They are all structurally complete with only some earthworks outstanding.
While construction of Msikaba from a technical point of view is demanding, in some ways the managing of relationships with surrounding communities is equally so. “We have worked very hard – and at considerable cost – to ensure that the project has the full support of surrounding communities and that the benefits stemming from construction are localised to the greatest extent possible,” says Savage.
Not only has the CME JV recruited about 70 % of its workforce locally – all of whom have been subjected to intensive on-site training – but it has also identified and supported a host of local SMMEs, around 40 in all, who have been appointed as sub-contractors and suppliers.
“The work allocated to them ranges from the fairly simple and straightforward, thatching for example, to quite major tasks,” Savage observes. “Some are supplying and operating ‘yellow metal’ and run fleets that include 30 ton excavators and 10 m3 trucks while others run steel-fixing teams, supply and operate batch plants or undertake road rehabilitation. We assist them with training and we also ensure they work safely.”
Summing up the Msikaba Project, Savage says that the final product will be a world class bridge showcasing the abilities of Concor and its JV partner MECSA. “We are proud to be part of this landmark project, which is uplifting local communities and which is also expected to have a substantial effect on economic growth in the Eastern Cape and KZN,” he concludes.
