Project summaryKampus is an exciting new £250m ‘garden neighbourhood’ being built on an old university site in the centre of Manchester. Contractor Mount Anvil is building two new 16-storey apartment blocks, extending a 13-storey tower of three floors and refurbishing two listed industrial buildings. By the Rochdale Canal and close to Piccadilly Station, the site will offer ‘secret’ streets, gardens and terraces in a unique location in this dynamic Northern Powerhouse region.
After being asked to assist with the construction, we provided all site services, from primary and secondary controls, grid lines setting out and as-built verification. We added manual monitoring, laser scanning and subsurface investigation from our large portfolio of services. Our experience proved vital in investigating an old culvert under one of the intended blocks.
Manchester has an interesting and ‘busy’ underground history, spanning canals, covered rivers, culverted streams and other industrial tunnels. It was therefore crucial for our client to know exactly what was beneath the site so that the construction work could be completed safely.
Our investigations found two tunnels running under the site. One, Duke’s Tunnel, has a fascinating past as it was used in the transport of coal from the Worsley mines along the Medlock River to the former London Road Wharf, now beneath Manchester Piccadilly station.
The tunnel was completed in 1789 but not used for long, as the Rochdale Canal was completed shortly afterwards, in 1800. The original entrance is still visible from the Medlock but the riverbed has silted over the years, leaving only the top of the arch visible.
The second discovery was Shooter’s Brook, a tributary of the Medlock River which was culverted and used as a surface water sewer. Many access points were visible, two on each side of the stream at Sackville Gardens and in the basement of the Piccadilly Place car park.
As the tunnels were respectively 12 and eight metres below the surface, traditional methods of detection such as ground penetrating radar or electro resistivity technology were not practicable. It was decided to attempt a survey in-situ using laser scanning techniques. Our company pioneered the use of laser scanning for commercial surveys in the early 2000s and continues to innovate and lead the sector today.
To assess the risks and establish a method statement, we carried out a CCTV survey which confirmed that both manholes were connected and the tunnel was clear of any obstacles. That meant it was technically and physically possible to carry out the survey in safe conditions.
Due to the access conditions and the dimensions in some parts of the tunnel, it was agreed to treat it as a high risk confined space. We used two “top-man” and two “bottom-man” teams, one for each entry point. Two CCTV crews were also assigned to keep permanent visual contact with the crews during the survey. After completing a walk-through, we decided the atmosphere was safe and it was agreed not to use breathing equipment, although an emergency one was on standby.
Once the supervisor had given the full brief, the survey started from the car park basement. Because all externals and the ends of the tunnel were already scanned and co-ordinated using precise traversing and linked to the Ordnance Survey Grid and Datum, the survey team simply started to scan from the centre of the chamber. They then leapfrogged along the tunnel, ensuring common targets were visible and there was a good overlapping between set-ups to allow an accurate registration of the data.
Once captured, the data was used to register the point clouds together and extract the outline of the tunnel so it could be overlapped with the above ground plot. The accurate mapping of the tunnel has allowed our client to design the piles.
Our team of experts; Matthieu Marsault (Project Manager), Thomas Townley (Senior Surveyor) and Danny Minshull (Junior Surveyor) delivered the project efficiently and in a timely manner. Special thanks to Industrial Water Jetting Systems Ltd (IWJS) for providing the CCTV and confined space assistance.
Our client knew only that the culvert existed between two manholes and realised that it needed to be mapped accurately to avoid the risk of piling through. Looking at the image below, we can clearly see it was the right decision.
Using our information, the client’s structural engineer was able to redesign the piles of the proposed 16-storey building and ensure a safety corridor around the culvert. A new manhole was also installed within the site for the surface water.
As we have shown with this successful project, we deliver services to equip our clients with the data and information they need to make critical decisions at every stage of their project or asset life cycle. With every scheme, we draw on the skills and experience of our people to deliver certainty our clients can trust.
For more information on this project, please contact Matthieu Marsault at firstname.lastname@example.org