WSP’s micro-tunnelling project breaks new ground and sets a new record

WSP’s project, which entails the planning, design and construction monitoring services for the Farm 694 development is set to bring significant benefits to Mitchell’s Plain communities.

Location

South Africa

Client

Western Cape Government Department of Infrastructure (Branch: Human Settlements)

Project Value

ZAR 176 million

Project Status

Construction phase completion date: March 2023

The project is intended to support the Western Cape Government Department of Infrastructure’s plan to develop several housing opportunities for the Kosovo Informal Settlement and the surrounding area. It will also support several other planned developments, as well as the densification of the Mitchell’s Plain area. The project will bring significant infrastructure development to the area, improving the living standards of the Kosovo community and surrounds.

The Farm 694 project is the first phase of the ambitious upgrade and enables de-densification of the larger Kosovo Informal Settlement, with a focus on bulk sewer and water services upgrades.

Owing to the project’s proximity to existing services and roads, WSP decided to use the contractor’s (Power Smart JV) alternative tender offer. The alternative tender proposed micro-tunnelling by the specialist sub-contractor CSV Construction (Pty) Ltd, as opposed to open-trench excavation, to minimise disruptions to the project and surrounding community. The micro-tunnelling technology also improved tolerances vertically and horizontally in the naturally flat area and proposed flat slope sewer line (1:1886 or 0.053%).

The project is significant for two reasons. Firstly, it has been minimally disruptive to local communities, due to the implementation of micro-tunnelling. While most projects of this class would have required conventional, open, and deep excavation, micro-tunnelling enables limited excavation along the bulk sewer and water pipeline route instead.

This is important, explains Du Toit Carstens, Technical Director: WSP in Africa Civils, as conventional excavation (up to 8 metres deep) would have posed major safety risks for both construction personnel and the public.

“The project is located within an existing developed area and the full extent of the pipeline is situated within an existing 4 metre servitude and existing class 3 arterial road. Conventional construction methods would have substantially impacted the surrounding community. Apart from major traffic disruptions, several public spaces, including parks and schools, would have had to be closed for the duration of the construction period for safety reasons,” Carstens elaborates.

Another reason that the project is notable, is because it has the distinction of being the longest length of pipeline (2.5km) and biggest diameter pipeline to be constructed within South Africa using the micro-tunnelling method.

WSP was appointed to this project by the Western Cape Government’s former Department of Human Settlements in September 2018 as a joint venture (JV). WSP was appointed for the planning, detailed design, and construction monitoring services whilst MPAMOT was appointed for construction monitoring and the contract administration services for the upgrade.

Construction commenced in August 2019 and the project was completed in March 2023, with the micro-tunnelling completed in March 2022. The full scope of the project included the installation of a 500-metre water main, including all associated pipe fittings and chambers along New Eisleben Road in Mitchell’s Plain; installation of 1250 metres of 1200 mm diameter sewer pipeline between Merrydale Road and Park Avenue, and the installation of 1150 metres of 1350 mm diameter sewer pipeline from Park Avenue along Spine Road to the Mitchell’s Plain Wastewater Treatment Works.

Furthermore, the project entailed the construction of all associated structural manhole chambers including installation of a new collection chamber at the Mitchell’s Plain Wastewater Treatment Works. In addition, the installation of a new Sand Trap structure along the sewer pipeline was constructed for the removal of grit and debris.

A project of this scope invariably has its obstacles, and this one is no exception. The COVID-19 pandemic was not the least of them, leading to unavoidable project delays. Yet the project team’s adaptability and collaborative approach helped to mitigate against these delays.

“One of the challenges was the continuous changes that needed to be made to the design during the construction phase, in order to accommodate unknown existing services. This was done either by temporarily relocating services, permanently relocating services or reconfiguring existing services,” explains Darren Osborne, Civil Engineer (Civil & Municipal Infrastructure) at WSP in Africa.

Another significant challenge was not knowing the total extent and accurate location of a major existing stormwater pipeline which clashed with the new bulk sewer pipeline. This is not uncommon in South Africa’s informal settlements, where documented plans and what has actually been built are often misaligned. WSP’s local knowledge and experience in overcoming these kinds of challenges played a key role in the project’s success. Digital engineering tools, like Civil3D, were used to enhance collaboration and timeously adjust designs to suite the circumstances on the ground and ensure accurate construction drawings.

“We managed to address these challenges by constructing temporary stormwater infrastructure including a siphon structure and sand trap during micro-tunnelling, and then micro-tunnelling a new stormwater pipeline section over the new bulk sewer pipeline after installation,” adds Arnaud Malan, Civil Engineer specialising in Water & Wastewater, WSP in Africa.

Despite the various challenges faced on this project, the professional team and appointed contractor remained committed to ensuring the success and completion of the project, which substantially benefits the surrounding communities. Working in the team’s favour is the fact that, if required to, the micro-tunnelling machine could be run 24-hours a day and merely requires a switching of operators. While this was only necessary a few times, it enabled the contractor to catch up any time lost when the need arose.

This gave comfort to residents in the area, as this project highlights the vital role that water and functioning infrastructure play in the lives of communities.

Mr Sandile T Gqoboka, Acting Director, Western Cape Government Department of Infrastructure, stated in letter to WSP, that The Department of Infrastructure would like to endorse the Kosovo Farm 694 Housing Development Project for its outstanding [work] and social impact in improving the livelihood of one of the vulnerable communities in the Western Cape. He further stated that the success of this project is a demonstration of a collaborative approach by Government, Private Sector and Community Stakeholders, contributing to social integration and promoting diversity within communities.

Off the back of this successful project, WSP’s Kosovo team co-authored a technical paper on slurry shield micro-tunnelling, which they co-presented with the City of Cape Town and CSV Civil Contractors at the South African National Council on Tunnelling (SANCOT) Symposium in 2023. Farm 694 Kosovo was also awarded the CESA AEON award for best project in the category R250 million to R1 billion in August 2024.

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