Construction World April 2015

PROJECTS AND CONTRACTS

The detail design for the rehabilita- tion and re-alignment of the road, including upgrades on 11 culverts, one river bridge and one road-over CHALLENGING ASPECTS of N5 rehabilitation Werner Venter, contracts engineer from the DMV/AECOM JV. Edgar Dube, project manager from SANRAL. >

re-routed through QwaQwa and for the remaining traffic on the N5 the time lost due to waiting for the blasting and clearance of debris was never more than one hour. Some sub-surface drainage challenges were encountered between km 20 and 25. After an on-site investigation, it was found that due to the high water table in this area, several natural springs existed in the road prism. This problem was solved using a herringbone system of sub-soil drains. The Elands River tributary culvert was done in 11 stages. The floor of the culvert was completed in total to allow for the collapsible internal shutter to be pushed along rails to the adjacent section. The shutter was then erected again only once the previous section had been cured. A total of 120 cub.m of concrete was cast for the walls and deck of each of the 11 sections. Proper care had to be taken with the fill adjacent and on top of the culvert. The final fill reached a height of 9,7 m above the top of the deck of the culvert. This implies a static load of 20 ton/m 2 of the culvert deck slab. The total static weight of material on the deck slab range in the order of 17 600 t. The new main Elands River Bridge has five spans, each consisting of 10 precast concrete beams. These beams are covered by an in-situ deck slab of 250 mm, with perma- nent precast shutters between all beams. The two abutments are supported by 4 piles each, which on average have been founded to a depth of 19 m, while piers 1 and 4 each have five piles in the order of 9 m deep. Piers

was found to be 3,3 m and a working space of 1,6 m was required for the adjacent construc- tion activities, road signs and flag people. There were, however, instances along the route where the road had to be constructed in third-width sections. Fortunately these were only applicable for about 8 km of the road. Traffic in these sections were separated during phase two to run both sides of the work zone, a situation which required extra care and effort from the contractor’s personnel. Another aspect that had to be intro- duced was the construction of temporary seals during the winter period to allow for the traffic to be transferred to the newly reha- bilitated road, as existing old road sections were deteriorating very quickly and became unsafe and uneconomical to repair. Winter seals have been an aspect of investigation and research by SANRAL and other entities like the bitumen manufac- turers and consultant/contractor companies to try and overcome the big loss in produc- tion during the embargo period for sealwork in South Africa (May to September). On the basis of these research findings, temporary sealwork was allowed with the use of a speci- fied bitumen emulsion [SC E1(t)] with 9,5 mm pre-coated stone, covered by a well designed slurry mix. Using this design the safe flow of the traffic as well as the construction produc- tion could be successfully maintained. The cuttings in the new alignment section were done by blasting up to the required levels. Traffic along the N5 was

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rail bridge, as well as the new in-situ culvert with a fill height of 9,7 m and wall thickness of 700 mm and the new Elands River bridge was done by the SANRAL appointed AECOM/ DMV Baeletsi joint venture. The construction works were scheduled to start in November 2012, but were delayed by environmental issues until April 2013. The construction time allowed for comple- tion of the project is 30 months. Currently, after 24 months into the project, work is well underway and the initial backlog is slowly but surely diminishing every month. Construction challenges The road rehabilitation specification has an embargo on the use of stop/go systems. The challenge, therefore, is to keep the traffic flowing in both directions while the opposite side of the road is being constructed. The available road widths at certain places were such that the traffic had to be accommo- dated on freshly built bypasses in the middle of the rainy season. This, at times, led to crisis management solutions to enable the free-flow of traffic. A rapid increase in heavy vehicles contrib- uted to the traffic accommodation chal- lenge on this project. The speed limit was reduced to 60 km/h at work zones assisted by the placing of removable speed humps. The absolute minimum road width to use

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CONSTRUCTION WORLD APRIL 2015