Tunnelling work starts on Chester's new drain
13 April 2021Underground tunnelling has now started on the surface water drain through Chester city centre.
The new drain will run south along St. Martin’s Way, Nicholas Street, Grosvenor Road and Castle Drive. It will be almost 1km in length, 1.2m in diameter and require 9 access shafts spaced along the route, each 7m wide and 12m deep.
The tunnel is being installed by VINCI Construction UK on behalf of Cheshire West and Chester Council.
The new drain will result in significant environmental protections and benefits. It will reduce flooding and drain bursts in the city centre; reduce the volume of water requiring sewage treatment; help cut energy use; and reduce untreated sewage discharges into the river during heavy rainfall when the current network is already at capacity.
Welcoming this important work, Andrew Lewis, Chief Executive of Cheshire West and Chester Council said: “The new drain is a major future-proof investment in Chester’s recovery from the pandemic, and an essential requirement ahead of our major regeneration schemes, including the Northgate development.
“This is the biggest infrastructure project in Chester for decades. We regret that it will result in some traffic disruption and inconvenience to nearby residents and businesses. Please bear with us as we work to complete this vital work as quickly as possible.”
Over 85 per cent of the tunnel will be excavated via a ‘pipe jacking’ process rather than an open cut to significantly minimise disruption above ground. This industry standard process uses a remotely controlled, laser guided tunnel boring machine with rotating cutting knives and discs that will be driven by a set of hydraulic rams in the base of each drive shaft along the route.
A closed slurry system allows the excavated rock to be brought to the surface separation plant and recycles the water used in the cutting process. As the tunnel boring machine moves forward along the route, sections of the new drain are lowered down the shaft and pushed along the tunnel behind the tunnel boring machine to form a continuous watertight drain.
Once the tunnel boring machine reaches the receiving shaft it is recovered, and the process starts again to excavate the next drain section and will end and at an outfall on the River Dee.
Garry Bowker, Regional Director for the Northwest of VINCI Construction UK Limited said: “We are delighted to commence the tunnelling phase of the new drain, our contractors will be using the most advanced technology available to ensure we can work safely and efficiently to deliver this critical project.
“Our ability to undertake this tunnelling project, as well as the main Northgate Phase 1 development, demonstrates the wide range of technical expertise we can offer as a business.”
Work on the new drain is currently expected to be completed by the end of the year when the Clockwise traffic diversions for the inner ring-road can be lifted, with construction of the Northgate development continuing until summer 2022.