SSI Engineers & Environmental Consultants, a black empowerment engineering and environmental consultancy – which forms part of the DHV Group – has been awarded the prestigious CESA Glenrand MIB Engineering Excellence Award for its work on the local Mgeni viaduct project.
In addition, it was recognised by the Durban Branch of the South African Institution of Civil Engineering 2010 Awards for “The Most Outstanding Civil Engineering Achievement – Technical Excellence Category”.
The Mgeni viaduct is a 410m long incrementally-launched bridge which forms part of the new main road P577 between KwaMashu and New Germany. This 14km long route will provide the fifth main crossing of the Mgeni River in the Durban region and is located about 10km inland from the coast. Completion of the P577 will provide a direct link between the residential areas of KwaMashu, Ntuzuma and Inanda with New Germany and Pinetown further to the west.
Planning and design of this road was completed in the mid-1990s but construction was delayed until 2002 due to lack of funds. The decision to proceed was based on the significant contribution the road would make to the socio-economic development of the local communities, linking them to new employment opportunities and dramatically reducing transport costs.
The site of the Mgeni viaduct is dominated by the steep rocky escarpment on the left (east) bank of the river, which falls sharply to river level and rises gently towards the west.
To give you an idea of the scale of the project consider: The viaduct comprises twin pre-stressed concrete box girder decks with a total of nine spans – one of 34m, one of 36m, six of 50m and one of 40m.
It is supported by eight 6m x 3.5m featured hollow piers varying in height from 18m to 45m, which were founded on intact sandstone at shallow depth and constructed by sliding. The four tallest piers required stays during launching to prevent excessive horizontal deflections.
Each deck is 3.7m deep by 15m wide and will carry three 3.5m-wide traffic lanes, shoulders and 1.5m-wide sidewalks at the outer edge. The twin decks are separated by a 0.5m gap, which is closed by heavy precast concrete T-sections to form a raised median between the carriageways.
The successful completion of this structure for the KwaZulu-Natal Department of Transport without major incident testifies to the quality of the contractor’s temporary works and control measures during the construction of this technically challenging project.
The SSI team involved in the planning, design and construction management of the Mgeni viaduct has been together since 1981 when the first incrementally launched viaduct in South Africa was constructed across the Umhlatuzana River adjacent to the Marrianhill Toll Plaza on the N3 near Pinetown. Bruce Durow has been intimately involved in the planning and design of both structures and Kurt Hillermann has been the resident engineer on both projects. The depth of experience of this team ensured that a high quality design was presented to the contractors.
Caring for the environment
The natural beauty of the bridge setting has been the inspiration for exceptional attention to the environment. The designers minimised the impact that the location of the substructure would have on the Mgeni River and site staff respected the requirements of the contract which imposed heavy fines for violations of environmental requirements.
The environment was a recurring theme during daily toolbox talks. Specific interventions were the relocation of indigenous trees and the recording and reinstatement of the riverine environment. Numerous audits were carried out and a clean bill of health was obtained.
The Department of Water Affairs gave the project its stamp of approval.
** Information provided by the South African Institution of Civil Engineering