East London Sheetpile
Rehabilitation of sheet pile quay wall at South Africa’s only river port
The Port of East London on the south-east coast of South Africa is the country’s only river port. In recent years, the Transnet National Ports Authority (TNPA) carried out a range of projects aimed at refurbishing and modernising the port’s infrastructure to sustain existing business and cargo traffic, as well as gear up for future growth.
One of these projects set out to rehabilitate the 83 m wharf adjacent to the Princess Elizabeth Dry Dock and Latimer Landing. Its old sheet pile quay wall was installed in 1942 and was past its 50-year design life. Corrosion holes in the steel sheet piles had resulted in loss of fines and the consequent settlement of the platform behind the quay wall, and replacing the old wall was recommended.
Zutari was appointed in 2013 to undertake the feasibility (FEL 3) study on the most appropriate design to rehabilitate the sheet pile wharf. After supervising and analysing a geotechnical investigation, Zutari developed a proposed design in more detail, which included making the structure resilient to the future sea level rise expected for the region. The proposal was to have a combined steel sheet pile wall with tubular piles, interspaced with AZ piles and installed in front of the existing sheet pile wall. A ground improvement scheme, reinstatement of services and pavement design also formed part of the engineering solution. In addition to providing structural engineering services, Zutari was also responsible for site supervision.
Responding agilely to the unexpected
During the installation of shear pins in front of the existing quay wall to secure its toe, the existing sheet pile quay wall was found to have its founding toe offset up to 1,000 mm to the waterside, compared to the top of the wall. This meant the design position of the new wall had to be changed and moved further into the waterside.
However, the contractor’s piling rig had a limited reach, beyond which the tubular piles could not be installed, and the steel tubular and sheet piles had already arrived on site. As a solution, a set number of angled tubular piles and sheet piles were made to form the curve of the wall towards the graving dock in an amended design.
The design approach was to provide an infrastructure solution that was as flexible as possible, considering possible changes in future user requirements.
Flexible design solution guarded against other issues
The FEL project life cycle process ensured that all possibilities were considered, and fatal flaws identified early in the option development process.
Factors influencing the evaluation process were:
- The extremely hard natural bedrock found on site during the geotechnical investigation, which would be difficult to excavate or penetrate
- The lack of evidence of fine-grained material in the lower fill material, which led to the conclusion that the original fine material had been leached out through the corroded existing sheet piles
The design approach was to provide an infrastructure solution that was as flexible as possible, considering possible changes in future user requirements.
Zutari developed a detailed construction sequence to ensure safe implementation of the design without overloading the existing wall, as well as a graphical sequence to illustrate each of the construction phases, assist with analysing the stability of the wall at each stage, and develop a safe and practical construction sequence.
Good collaboration the key to success
The good and robust collaboration within the project team, including the designers, contractor and the client, enabled the project to be successfully implemented within time and budget. The Zutari project team was applauded by TNPA for their responsiveness, level of engagement, and positive contribution towards project working relationships.
*The Aurecon Africa business has been officially renamed Zutari as at 21 July 2020. Zutari acquired Aurecon Middle East on 20 November 2020.
