North Hykeham Relief Road Mains Diversions (2026)
Installation of PE pipe within a protective sleeve - Courtesy of @one Alliance
Construction of the North Hykeham Relief Road is progressing in Lincolnshire, creating a new strategic link between the A46 Lincoln roundabout and the A15 Sleaford Road roundabout at the southern end of the Lincoln Eastern Bypass. The scheme, delivered by Lincolnshire County Council (LCC), includes new junctions at South Hykeham Road, Brant Road and Grantham Road. As the route has developed, several existing Anglian Water assets have been identified within the footprint of the proposed highway infrastructure. To enable construction of the new road while maintaining the resilience and performance of the water network, a significant programme of water and wastewater diversions has been required.
Project need
Working on behalf of Anglian Water, the @one Alliance was tasked with delivering a £5.6m programme of asset diversions to support the wider highways scheme. The programme comprises the diversion of eight potable water assets and one wastewater asset, with the relocation of approximately 4km of buried infrastructure across multiple locations along the route.
The works extend along South Hykeham Road, Station Road, Grantham Road, Sleaford Road and Wath Lane, affecting assets ranging from local distribution mains to strategic trunk infrastructure, including a 500mm water main.
Showcasing the proximity to the A607 – Courtesy of @one Alliance
Several existing pipelines directly conflict with the alignment of proposed roundabouts, roads and associated structures. At the A46 roundabout, three potable water mains are affected by the highway proposals, comprising two 180mm mains and one 125mm main, requiring the installation of approximately 614m of replacement infrastructure.
Elsewhere, an existing 90mm water main along South Hykeham Road is being diverted to facilitate construction of a new roundabout, while an existing 180mm main on Station Road requires relocation to accommodate a proposed roundabout and bridge crossing.
Challenges
The principal challenge has been to deliver these diversions safely, maintain uninterrupted customer service and coordinate works alongside a major highways construction programme with multiple stakeholders and interfaces. Some of the most technically challenging works are at Grantham Road, where both a 500mm and a 355mm potable water main require diversion. At Sleaford Road, a further conflict arises with an existing 300mm raw water main that lies within the footprint of a proposed roundabout.
The solution
To align with the North Hykeham Relief Road construction programme, the @one Alliance adopted a phased delivery strategy, sequencing diversions to ensure assets are relocated ahead of the relevant highway works.
Successful delivery has required close collaboration among Anglian Water, Lincolnshire County Council, the design and construction teams, and the wider supply chain. This coordinated approach has minimised programme clashes and enabled the wider infrastructure scheme to progress as planned.
Installation of the new pipes – Courtesy of @one Alliance
A combination of open-cut construction, sleeving and slip-lining techniques has been used throughout the project, with installation methods selected to suit local conditions, existing utilities and future highway requirements.
At South Hykeham Road, the existing 90mm main is being replaced with PE100 pipework. Sections of the new main are being installed using open-cut methods, while sleeving and slip-lining techniques are being used where crossings of proposed highways and existing services are required.
The Grantham Road diversions involve two of the programme’s largest assets. The existing 500mm water main is being replaced with a new 560mm PE100 pipeline, while the existing 355mm main is being replaced on a like-for-like basis with a new PE100 asset.
Both mains are being installed along a common route, with appropriate separation maintained throughout. Where the alignment crosses Grantham Road and the proposed highway infrastructure, protective sleeves are installed to facilitate future maintenance access and provide additional asset protection beneath the completed road.
At Sleaford Road, the existing 300mm raw water main is being replaced with a 355mm PE100 main. Installation is being carried out using a combination of open-cut construction and sleeved crossings beneath the proposed highway and access infrastructure.
Hydraulic modelling has played a key role in developing each diversion design, ensuring that the replacement assets maintain network performance after relocation.
Newly installed pipework ready to be backfilled – Courtesy of @one Alliance
For example, modelling undertaken for the Grantham Road 500mm main confirmed that a 560mm PE100 replacement would accommodate potential maximum flows without creating unacceptable hydraulic constraints. Similarly, the replacement 355mm main delivers equivalent hydraulic performance to the existing asset.
Modelling at Sleaford Road showed that the proposed 355mm PE100 pipeline delivers hydraulic performance comparable to that of the existing 300mm ductile iron main and maintains sufficient capacity to support flows from Dunston Water Treatment Works.
This design-led approach has enabled the project team to develop solutions that meet operational requirements while remaining practical and efficient to construct.
North Hykeham Mains Diversions: Supply chain – key participants
The successful delivery of the diversion programme has relied on collaboration among Anglian Water, Lincolnshire County Council, the @one Alliance and a specialist supply chain, including:
- Project delivery: @one Alliance
- Main contractor: Balfour Beatty
- PE pipework: Aliaxis
- Ductile iron pipework & fittings: Saint Gobain PAM UK
- Valves & hydrants: AVK UK Ltd
- Fittings & ancillary materials: Wolseley UK
- Recycled aggregates: Richardson Recycling
- Reinstatement works: CPC Civils
- Surfacing & reinstatement works: WN Surfacing Ltd
Benefits of the solution
The principal benefit of the programme is that it removes a major infrastructure constraint, enabling the construction of the North Hykeham Relief Road while maintaining the integrity and operation of Anglian Water’s network. By relocating affected assets ahead of highway construction, the project eliminates conflicts between existing buried infrastructure and the proposed road layout, thereby reducing delivery risk for both programmes.
New valve fittings installed within an excavated trench, ready for connection and reinstatement – Courtesy of @one Alliance
The scheme also provides an opportunity to replace ageing assets with modern polyethylene pipework, helping to enhance long-term network resilience and operational reliability.
Where appropriate, asset sizes have been increased following hydraulic assessment to ensure sufficient capacity is maintained to meet future operational requirements. This ensures the new infrastructure not only accommodates the highway scheme but also supports the ongoing performance of the water network.
The use of sleeving and slip-lining techniques has enabled the project team to overcome numerous site constraints, limiting disruption and reducing the extent of excavation required in sensitive locations.
Equally important has been the phased delivery approach. Given the multiple interfaces between water infrastructure and highway construction, careful planning and coordination have been essential to maintaining programme alignment across all stakeholders.
As the diversion works progress towards completion, the majority of assets have now been successfully addressed, bringing the wider highway scheme significantly closer to delivery.
Conclusion
As construction of the North Hykeham Relief Road continues across Lincolnshire, the £5.6 million Anglian Water mains diversion programme is nearing completion. The project has involved diverting eight potable water assets and one wastewater asset, requiring approximately 4km of infrastructure to be relocated to accommodate the new strategic route. From local distribution mains to critical trunk infrastructure, including a 500mm water main, the programme has presented a diverse range of engineering and construction challenges.
The @one Alliance has addressed these challenges through a combination of detailed hydraulic modelling, phased delivery, open-cut installation, and sleeving and slip-lining techniques, ensuring the network’s operational performance is maintained throughout construction.
Laying new pipes near the Sleaford Road roundabout – Courtesy of @one Alliance
The project also highlights the importance of early engagement and collaboration where water infrastructure intersects with major transport schemes. By working closely with Lincolnshire County Council, Anglian Water and the wider supply chain, the team has successfully coordinated complex diversions while supporting progress on a major regional infrastructure investment.
As the final connections and commissioning activities are completed, the programme will remove a significant constraint on the highway route, enabling delivery of a key transport link while ensuring Anglian Water’s assets remain resilient, accessible and capable of serving existing and future customers.
The successful delivery of the North Hykeham Relief Road mains diversions demonstrates how effective collaboration among water companies, infrastructure alliances, local authorities and specialist contractors can enable the safe and efficient delivery of multiple major projects within a shared corridor.
Excavated material being loaded and transported around the site - Courtesy of @one Alliance
