Milestone
Tunnel boring machine breaks through at Knutsford treatment works
By Staff Writer | 17 August 2026
A 40 tonne tunnel boring machine has completed the first stage of its underground journey at Knutsford, breaking through at the town's wastewater treatment works as part of United Utilities' 48 million pound sewer network upgrade.
The breakthrough was announced on 12 August 2026. The machine, named Lily by pupils at Bexton Primary School after the nearby River Lily, began its drive from Parkgate Industrial Estate before breaking through at Knutsford Wastewater Treatment Works in Cheshire.
The machine will now return to Parkgate and be lowered underground for the second part of its journey, travelling in the opposite direction to Moor Pumping Station near Moor Pool.
The scheme will provide additional stormwater storage and improve water quality in Moor Pool by installing a 1.8 kilometre storage tunnel between the pumping station at Moor Pool and the wastewater treatment works in Knutsford. Once complete, the tunnel will be 20 metres underground at its deepest point and two metres in diameter, and will store up to five and a half million litres of stormwater in periods of heavy rainfall before it is treated at the Knutsford works.
Maria Fletcher, United Utilities' County Business Lead for Wastewater in Cheshire, said: "This is also a remarkable feat of engineering, delivering major underground infrastructure that will store up to five and a half million litres of stormwater in periods of heavy rainfall."
The company states that the project forms part of a wider programme in which it will spend more than 13 billion pounds over the next five years across the North West, covering rivers, lakes, bathing waters and drinking water supplies.
What the practitioner should take from this
A double drive from a single launch site is an economical way to build a tunnel of this length, and it concentrates programme risk in one machine. Between the two drives the machine must be recovered, returned to Parkgate, inspected and relaunched, and every one of those operations sits on the critical path with no parallel working possible. The practitioner should ask how the contract treats machine breakdown and cutterhead intervention time: on a two metre bore there is no man entry access to speak of, so an intervention means recovering the machine, and the delay analysis should recognise that from the start.
Ground risk on a drive beneath a town deserves the usual scrutiny of the baseline. Where a geotechnical baseline report exists, the boundary between expected and unexpected conditions is a drafting choice made before tender, and it decides who pays when the machine meets something the borings did not show. Where no baseline was set, the argument arrives unstructured, which is worse for both parties.
The five and a half million litre storage figure also carries a quiet lesson for anyone pricing storm storage schemes under the current investment programme. Performance is stated as a volume and an outcome, fewer storm overflow activations, and the regulator measures the outcome. Whether the contractor's obligation ends at building the stated volume, or extends to the performance the volume is meant to deliver, is a distinction the contract should draw expressly.
None of that reflects on this project, where no dispute has been reported. It is the ordinary commercial anatomy of a small bore storage tunnel under a market town, and the baseline documents agreed before launch are the ones that matter when the machine goes back in the ground.