Construction World June 2017

PROJECT PROFILE: ROADS AND BRIDGES

The project which started in March 2016 is on track and scheduled for completion in the first quarter of 2019. Significantly this project, an initiative of the South African National Roads Agency SOC Limited (SANRAL), is currently one of the largest road infrastructure developments underway in the country. Scope It includes the construction of a new two-lane northbound carriageway, rehabilitation of the existing southbound carriageway and a large number of structures including bridges, overpasses, culverts and drainage. Bulk earthworks will amount to 800 000 m 3 , with layerworks requiring 400 000 m 3 of material and some 220 000 t of asphalt. The total concrete volume is 37 000 m³, of which the ancillary works will use over 16 000 m 3 of concrete. Contracts manager at Murray & Roberts Infrastructure, Jonathan Pearce says the project features the full array of civil engineering activities and includes the construction of 21 major culvert/under pass extensions and 11 bridges. The construction of two major river bridges on the northbound carriageway is on the critical path and work on both has begun. Preserving the environment Pearce explains that all the requisite environmental assessments have been conducted, and construction work is being done in accordance with these. This is in line with Murray & Roberts Infrastructure’s solid commitment to preserving the environment for future generations and ensuring minimum harm to the areas in which construction is taking place. The water use licence dictates stringent measures as to how the rivers may be worked in as well as restrictions to limit the footprint in and around these areas. In addition, there are strict rehabilitation programmes in place for after contract completion. Bridge construction underway The larger river bridge being constructed is over the Mhlatuze River which has its source over 100 km away. The river catchment area supports agricultural and industrial activities before it forms an estuary as it flows into the deep water port of Richards Bay. The Mhlatuze Bridge will be 240 metre long and have a total of 70 900 mm diameter bored piles with oscillated liners below seven piers, some to a depth of 65 metres to reach competent founding material and ensure adequate load bearing capacity for the final structure. The bridge construction consists of eight deck spans com- prising a total of 48 30 metre long post tensioned beams. Each span has six 1,83 metre high beams which are cast elsewhere on the site. proposed construction programme from 40 months to 37 months on the contract to construct 33 km of dual carriageway on the N2 between the Mtunzini Toll Plaza and Empangeni interchange on the KwaZulu-Natal North coast. By offering an alternative construction methodology, Murray & Roberts Infrastructure reduced the FIRST BRIDGES ON N2 contract in KZN under construction

“Complex geological conditions encountered in this area, with stiff clay that has similar properties to soft rock found at around 35 metres, has caused delays in completing the piling activity”, Pearce says. The stiff clay creates a syringe-like effect on the piling casings causing complications when liner extraction takes place. “While delays have put pressure on the construction, we are adapting our construction schedule to ensure that we meet the deadline and SANRAL expectations,” he says. The second major bridge under construction is over the Mlalazi River and has its own set of challenges, largely emanating from the inclement weather experienced during February and March this year. Being so far up the KZN north coast, the tail end of cyclones in the Madagascan channel normally hit the region bringing heavy rainfall and major flooding. This was, indeed, the case with cyclone Dineo in February with rainfall reaching more than 300 mm in 72 hours. The Mlalazi River is tidal and although the bridge is situated some 12 km from the ocean, the water level between tides can rise and fall by up to a metre. Geo-synthetic sand bags have been used to create working platforms to provide an adequate water channel with minimum environmental impact while providing safe working conditions. The specialised sand bags provide an effective seal between the water and the construction works, preventing any seepage, such as unnatural siltation, from the construction site into the river channel. The Mlalazi Bridge will have a final span of 120 metres with three piers and two abutments. Ten piles per pier, to a depth of 25 metres each, will support two of the piers and one abutment. A total of 28 post-tensioned precast beams will be placed on top of the piers and abutments “Apart from the John Ross interchange bridge, yet to be constructed, and the extension to existing overpasses currently being built in-situ, precast beams will be used. This has allowed the construction process to be sped up and has negated the need for extensive scaffolding and formwork along this busy national route,” Pearce says. The precast yard is situated in a location that allows the beams to be easily transported to where required for installation. “Access to the structural and ancillary works was given special attention as the bulk of the works could not be accessed from the N2 highway. This necessitated optimisation of vehicle usage and haulage routes to remain as productive and cost effective as possible.” As on all Murray & Roberts Infrastructure sites, safety is a major focus and on-going safety training ensures that workers comprehend potential risks associated with construction activities and how to work towards a Zero Harm goal. On this particular construction programme, special attention has been placed on working at height given the number of high structures being built. “Another mitigating step to ensure optimum safety of workers on the highway during construction activities was the building of scaffold towers to enable workers to cross the N2 to the side where work needs to be done,” Pearce concludes. Murray & Roberts Infrastructure is a division of Murray & Roberts Construction which has been purchased by a consortium led by the Southern Palace Group of Companies, creating the first major black-owned infrastructure and building construction business in South Africa. 

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CONSTRUCTION WORLD JUNE 2017 CONSTRUCTION ORLD JUNE 2017