Construction World December 2018

Consulting Engineers

WINNER

REHABILITATION OF MAIN ROAD BETWEEN ATLANTIC ROAD, MUIZENBERG AND CLOVELLY ROAD, CLOVELLY – PHASE 3 The lack of space and the need to keep all services functioning throughout the project led to the use of a number of unconventional construction methods.

considerably due to the aesthetic benefits, as well as the increase in off- street parking areas. The employment of a firm of Professional Public Liaison Consultants has proven to be invaluable in terms of keeping the public informed on all matters and happenings concerning the project on an on-going basis. Design innovation The existing ground conditions were determined to consist of a bouldery mountain screen material with the top of the bedrock in places being several metres below the railway line in most areas. This precluded the use of any form of normal excavation technique in order to construct the foundations for the Clovelly retaining wall on the bedrock. Mini-piling was initially investigated but the wall would have required a total of in excess of 250 piles and the time required to construct them, the very limited space and the cost of the operation resulted in a better solution being sought. The solution selected was the use of Uretek Soil Stabiliser, which was pumped into the founding scree material using injection tubes set out on a 1 m by 1 m grid. The Uretek system works by injecting expanding geo-polymeric structural resins deep into the ground through small holes. This improves the quality of the foundation soils to the required bearing capacity and it can also be used to raise the level of the retaining wall should this be required in order to correct for any settlement. These tubes were cast into the mass concrete footing and a second round of material injection was carried out after the mass concrete had been constructed. The mass concrete footing was monitored using laser levels and as soon as it commenced lifting then the injection was ceased as this confirmed that all voids were satisfactorily filled. In retrospect, it would have been very difficult to utilise any other method. Environmental Impact Consideration From the start of the project, an extensive Community Liaison as well as Environmental awareness programme was run by Chand Environmental. They served as the public liaison consultants from Phase 1 in 2008 until the completion of Phase 3 in January 2018.

Construction innovation technology The lack of space and the need to keep all services functioning throughout the project led to the use of a number of unconventional construction methods. The method of pipe cracking was adopted for the replacement of the existing foul sewer. The new pipeline is comprised of butt-welded 250 mm diameter HDPE pipes, which were jacked into place between manholes. The use of Waterbound Macadam for the subbase was an innovation as this method of layer works has not been widely used in recent times. It proved to be an invaluable as the Waterbound Macadam could take temporary traffic accessing adjacent properties immediately and could be repaired very easily in areas where trenching was required. After trials aimed at trying to vibrate the sand in dry proved unsuccessful, it was changed to a wet method of washing in the sand using water and this was very successful. This was only used as there was extensive subsoil drainage provided under the kerb line on both sides of the road. The Uretek grouting, soil stabilisation method is the first time in South Africa where it has been used to create the required founding conditions for a structure the size of the Clovelly Retaining Wall and in such constrained conditions. Corporate Social Investment Due to the highly mechanised nature of the Project, there was limited scope for the utilisation of local labour however this was maximised where possible. One very large labour based component was the hand cut sandstone cladding that was applied to almost all of the Clovelly Retaining Wall, which was prepared and applied by a local team of stone masons and labourers who they trained up for the project. Despite all the difficulties and complexities described above, it is considered that the newly rehabilitated Road, Services and the Ancillary works have considerably enhanced the attractiveness of this popular and historic transport corridor. It has been reliably learned that property values along the completed sections of road have increased

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