Construction World December 2018

Civil Engineering Contractors

C hallenges included limited time for reconstruction due to ongoing erosion, tidal working, lack of working space for machines, beach access only, wave breaking during high tides, continuous sand movement, safety of the public, prevention of excavated concrete migrating to sea, excavation below water alongside existing structures and durability requirements for the marine environment. The difficult nature and limited scale of works demanded innovative methods of working. The solution of a mass concrete footing founded on bedrock and a reinforced concrete seawall was successfully completed and demonstrates the effective use of concrete as a permanent coastal protection solution. Restricted excavation between an old existing seawall and the now defunct seawall was required to be carried out down to the bedrock level at -2.0 MSL (mean sea level). This was within the tidal zone on An existing concrete seawall, located in the beach intertidal zone of a seafront property in Kleinbaai, was undermined during a worst-ever recorded sea storm in 2017, and in the process of collapsing into the sea. Undermining of an existing gravity main foul sewer and three-storey house structure directly behind the wall was inevitable. Repair of the wall was no longer feasible, making urgent reconstruction the only option. REPLACEMENT OF SEAWALL ERF 234, BLOUBERG STRAND

HIGHLY COMMENDED

the beach: A mass concrete foundation, embedded on the bedrock, for a new and reinforced concrete seawall to safeguard the existing three- storey house and surrounds. CSV Construction proposed to make use of interlocking Nippon Type IV steel sheetpiles to be installed to form a cofferdam within which the excavation could be carried out. The failed seawall was constructed a number of decades ago with its foundations placed on top of a layer of sand that overlaid bedrock at -2.0 m below MSL. At the time it would have been challenging to excavate below the sea level to be able to build a founding structure directly on top of the preferred bedrock. During a severe sea storm in 2017 the sand was washed from the beach on a large scale resulting in the seawall’s foundations to be undermined. This caused the wall to lean forward, about to topple. WSP Consulting Engineers, in consultation with Southern Oceaneering Marine Contractors and CSV Construction was able to design the new wall to be constructed, anchored directly onto the bedrock level at 3,5 m deep below ground level. The steel sheetpile cofferdam solution offered by CSV Construction enabled the Engineers to design the permanent structures to be constructed within the confines of the temporary works that were constructed under extremely challenging conditions, within the tidal wave zone. The project has since been completed successfully with no damage to the existing buildings and providing peace of mind against the onslaught of the ocean for years to come. 

PROJECT INFORMATION

• Company entering: CSV Construction • Client: Hartwig Trust • Contract value: R7-million • Start date: May 2018 • End date: September 2018 • Main Contractor: Southern Oceaneering • Principal Agent: WSP Group Africa • Consulting Engineer : WSP Group Africa • Specialist Contractor: CSV Construction

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