- Water
- 08 Aug 2025
Client: Thames Water
Duration: June 2023- ongoing
Situation
The Millennium Main is a 1000mm trunk main transporting portable water from Nunhead Reservoir to Deptford to support population growth and supply to the Greenwich Peninsula.
Tunnel sections of the pipeline had experienced failures in the past and the glass reinforced plastic pipes had deteriorated with extensive blistering, leading to concerns that the pipes were no longer serviceable.
M Group Water has been working with Thames Water to carry out site investigations, identify a cost- effective rehabilitation solution and deliver a £21m project to rehabilitate this trunk main using a hybrid lining system.
Task
In 2021, our team began investigating the status of the pipe annulus grouting to provide Thames Water with a cost-effective solution for repair. Using an innovative technique of pipe penetrating radar and geophysics, we were able to provide an accurate assessment of the state of the main.
As part of the site investigation, pipe wall samples were taken from GRP pipes to test pipe strength and analyse their composition. The results showed that the GRP pipes should have more than 30 years remaining asset life if the grout annulus were fully reinstated.
We wanted to find a solution to resolve the complex challenge of reaching and repairing voids in the annulus without causing additional strain and stress on the pipe, by pushing a material through the pipe, using a standard cement bound material and drilling.
Action
Following the review of several lining solutions, the decision was made to reline the pipes using a hybrid liner, considering the whole life cost, pipeline hydraulic performance , construction period and other risk factors.
Our team worked to rehabilitate the Millennium Main, ensuring compliance with Regulation 31 UK’s Water Supply (Water Quality Regulations) on our chosen technique as this approach had not been undertaken in England Wales at this point.
Since June 2024, the team has used innovative rehabilitation techniques for the main. Pipe Penetrating Radar (PPR) and geophysics identified trunk main voids, reducing confined space entry and costs.
Collaborating with Water Service Group and AECOM, we used PPR to survey the main, allowing AECOM to use geophysics to pinpoint drilling locations to confirm anomalies. PPR also located grout ‘sinking’ around the pipe.
In a first for portable water, Bacel® Hardform was used to fill the voids, restoring the pipeline’s structure. Additionally, we partnered with VIP Polymers to modify the VIP WECO seal, achieving Regulation31 approval and delivered savings of £15 to £20m against traditional methods.
During the development of the hybrid liner, an above-ground mock-up of the lining system was built to refine the detailed arrangement of the hybrid liner, to test the installation of the lining system, and to check if the installation work could be carried out safely during the actual installation.
Result
We began the installation of the hybrid liner in June 2023. The works within the pipes and tunnel shafts were carried out by our operatives who were qualified for high risk confined- space work.
A total of 973 hybrid liner units were installed in the GRP pipes and each unit was tested by air pressure to check leak tightness of the liner unit.
Benefits and outcomes included:
· Reducing confined space working for our operatives.
· The use of an innovative, new product which has a life expectancy of over 150 years.
· Excellent collaboration between our client and partners to get asset approval for use of new product.
· Finding innovative solutions that challenge existing methods.
· Reduction in grout holes, which could have weakened the pipe further.
The main is currently planned to return to service in August 2025.
“By working collaboratively with our client and partners to tackle a major challenge, we challenged our own processes, and the asset standards of our client, to deliver a cost effective, sustainable, and safe solution.” Nigel Butler, Contracts Director at M Group Water.
