Supply Chain - Site Preparation - Temporary Holding Tanks

Northumbrian Water’s County Durham and Tees Valley Pipeline, which is approximately 57km in length, is designed to improve water quality and increase resilience and operability within the Tees Network. The pipeline will replace existing potable water mains across the North East of England, some of which are more than 150 years old. The new pipeline will connect Lartington Water Treatment Works (WTW) to service reservoirs at Whorley Hill and Shildon, and the route includes a major crossing of the River Tees, 12m below the riverbed. Upon its completion, the pipeline will serve approximately 200,000 customers and link strategic assets serving Barnard Castle, Darlington, and Teesside, improving overall system resilience. Construction began in November 2023 and the project is currently progressing well on site. Cross country pipeline installation

The full route of the steel welded pipeline (Phases 1 & 2) includes crossings of the A1 motorway, three river crossings and two railway crossings. Farrans Construction is contracted to deliver Phase 1 of the project, the pipeline from Lartington to Shildon Service Reservoir, via Whorley Hill Service Reservoir. The chosen pipe material is robustly coated thin-walled steel, with individual pipe lengths of varying sizes (14m maximum) and generally 800mm in diameter. The Phase 1 pipeline is approximately 34km in length, including a section of twin 800mm diameter pipe, with one of the sections forming the starting point for Phase 2.

Shafts & tunnel at River Tees

Various options were explored to determine the most suitable method of the crossing of the River Tees, near Cotherstone Village, Barnard Castle, including pipe bridges and open cut trenches in the riverbed. However, there were several constraints that limited the viability of these options, including significant aquatic life disturbance and differing riverbank heights. The chosen option for the crossing was the construction of a tunnel under the river between two access shafts. The eastern shaft is approximately 46m deep and 7.5m diameter, whilst the western shaft is approximately 32m deep and 8m diameter, with the difference in shaft depth due to the rising topography of the eastern bank of the river. Each shaft has a 221 tonne reinforced concrete base.

Farrans Construction appointed Joseph Gallagher Limited, an experienced specialist shaft and tunnelling contractor, to construct the river crossing under a sub-contract arrangement.

[caption id="attachment_14149" align="alignnone" width="1200"] Pipe laying - Courtesy of Farrans Construction[/caption] Project Pipeline - County Durham & Tees Valley: Supply chain - key participants NWL designer - pipeline, tunnels & EIA: Mott MacDonald NWL designer - pipeline & connections: Stantec UK Design & construction: Farrans Construction Lead design for Farrans: AtkinsRéalis Tunnel design & construction: Joseph Gallagher Ltd Planning consultants: Lichfields Land management consultant: Bell Ingram Land drainage design: Land Drainage Consultancy Ltd Drainage installation: DMJ Drainage Ltd Groundworks: GR Potter Contracts Ltd Archaeological surveys: ECUS Ltd Geotechnical surveys: Dunelm Geotechnical Seismic surveys: Rees Onshore Seismic Ltd Trial holes at strategic connections: Waitings Ltd Slide rail shoring: National Trench Safety UK De-vegetation of hedgerows: ATM Ltd Steel pipes: FT Pipeline Systems Pipeline welding: Environmental Fabrications Ltd Pipe laying & associated welding: Grant Plant Hire Ltd Weld testing: Responsive Engineering Pipe fittings: George Green (Keighley) Ltd Pipe fittings: APP Fusion Ltd Pipe fittings: Franklyn Yates Engineering Ltd Pumps: Pioneer Pump Solutions Underpressure connections: UTS Engineering Ltd Shaft segments: Macrete (Ireland) Ltd Tunnel precast pipes: FP McCann Supply/install temporary bridge: Groundforce Silt fencing & flumes: JR Hind Ltd Shaft & tunnel construction

To construct the shafts and tunnel, the first 2m of rock was excavated and 1m shaft segments bolted together to form a ring. The rings were surrounded with an in situ concrete ‘collar’ to provide structural integrity and ‘set’ the shafts. These rings were checked for plumbness, as this is critical to ensure the overall verticality of the shafts.

Excavation began with each subsequent precast concrete segment ring bolted to the underside of the one above, known as underpinning. To provide structural support, the rings were then back grouted through holes in the segments. This process was repeated with each new metre of rock that was broken, installing the next ring of concrete segments until the required depth was reached. The excavators and mechanical breakers used were relatively small for the hardness of the ground and the excavation depth, due to the constricted dimensions of the two shafts. The excavation process began in June 2023 and was completed in March 2024.

Once the shaft construction was complete, the bases were poured, followed by installation of the 2.24m diameter tunnel boring machine (TBM). The TBM system has a hydraulic jack that pushes it forward through the ground as it excavates the rock strata. The TBM was launched on rails from the east drive shaft. Following the excavation of the rock, the hydraulic jacks were retracted and a 2.5m section of precast reinforced concrete pipe was lowered onto the launch railing at the bottom of the shaft using a 70 tonne crane. The hydraulic jack re-engaged to push the new length of pipe behind the previous one and continue pushing the pipe and TBM forward. The tunnel is 220m long, which required 88 (No.) 2.5m long pipes segments.

The ground material, that consisted of abrasive sandstone and other materials such as quartz, caused significant wear on the cutter heads and pumps of the TBM. This slowed the excavation process significantly, but continuous work by Joseph Gallagher meant that an average of four pipe sections, or 10m of earth, were still excavated each day.

Video captures the moment tunnel boring machine completes journey under the River Tees

The concrete tunnel acts as a sleeve for the water pipes that will transfer the water supply under the river. Two parallel pipes were used to provide water supply security in case one should fail, and ductile iron was selected as the pipe material to provide additional strength and resilience. Due to the constricted diameter of the shafts, the pipes were lowered down in 5.5m sections, with each section of the pipe being joined to the next as they were fed into the tunnel. Spider supports were used to locate the pipes which were winched through the tunnel from the east to the west shaft. The spider supports, which were used as spacers, were clamped to the pipes at regular intervals and hold the pipes steady as they are pulled through the tunnel. Once the pipes were completed and tested, they were sealed, and grout was pumped in to fill the remaining void space.

Once all piping works are complete and the pipes connected to the cross-country pipeline, the shafts will be backfilled with sand to make future excavation easier should it be required. Approximately 3,500 tonnes of sand will be needed for the eastern shaft and 2,500 tonnes for the western shaft.

Management of ingress water

During construction of the shafts and tunnel, the hydrogeology of the area and consequent water ingress made the excavation technically difficult. During excavation, there was up to 45 litres/second water ingress in the western shaft; the wettest of the two shafts. To manage this, the water is continually pumped out into a lagoon system located 50m away. The water is then processed in lamella clarifying units, which remove fine sediments, to ensure the water meets the required environmental standards to allow it to be pumped into the River Tees. This was an extensive water management operation, conducted under a permit issued by the Environment Agency, ensuring all activities complied with regulatory requirements and environmental protection standards.

[caption id="attachment_14146" align="alignnone" width="1200"] Water processing lagoons - Courtesy of Farrans Construction[/caption]

The water management issues continued after the shafts had been excavated, and it was decided that the western shaft would require a concrete plug to be inserted beneath the base slab to halt further water ingress. Consequently, the team had to excavate deeper than originally anticipated so that the plug would not interfere with the tunnel alignment. The plug, which is 2.7m thick and made of approximately 167m3 of concrete, was left to cure for seven days before the water was pumped and work began on the shaft’s structural base. A plug was not required for the eastern shaft.

Environmental constraints

There have been numerous environmental constraints that have had to be considered and mitigated during the project. A prominent issue facing the construction activities is compaction of excavated soil leading to soil degradation. When soil is compacted, the pore spaces within the soil are reduced, leading to poor soil structure and the erosion of the soil surface layer. To mitigate against this, the topsoil is stripped, stored, and only reinstated when in a suitable, friable condition. Low ground pressure tracked vehicles are also used on the site and traffic restricted prior to topsoil stripping. The topsoil and subsoil are then segregated and stored according to DEFRA codes of good practice.

Construction activities within freshwater environments can pose a significant threat to aquatic life through the release of pollutants, including silt and sediments. Fluming was therefore implemented in several local watercourses to minimise pollution and sedimentation by isolating construction areas and diverting the natural flow of water through temporary piping.

[caption id="attachment_14147" align="alignnone" width="1200"] Topsoil bund at Lartington - Courtesy of Farrans Construction[/caption]

Before fluming was implemented on site, several fish species, all of which are sensitive to almost all types of anthropogenic disturbances, had to be captured and safely relocated. Electrofishing was used to temporarily stun the fish so that they could be collected and moved to a safe location, ensuring the protection of several important species including salmon and trout. The combination of flumes and electrofishing minimised the disruption to the ecosystem, whilst regular monitoring ensured the flume remained effective, preventing leaks and blockages, and allowing for the assessment of fish population health and diversity.

Ground nesting birds were also present at some locations along the pipeline site, including populations of lapwing and curlew; both of which are listed on the UK Red List of Birds of Conservation Concern. To minimise disturbance to these species and other protected species such as badgers, great-crested newts, bats and otters, work was suspended during the nesting/breeding season. In addition, any active nesting sites located near the site were protected, and local authorities such as Natural England and the Environment Agency, were consulted.

Social value & community engagement

Community and stakeholder engagement has been a crucial part of the project to date, with Farrans delivering several schemes in line with Northumbrian Water’s values. Farrans began the engagement process through a ‘Meet the Contractor’ event, held in a local parish hall with attending stakeholders including community groups, local schools and colleges, parish councils, local businesses, and residents. A digital Microsoft form was also sent out to capture the thoughts of those who could not attend the event.

Representatives from Northumbrian Water were also present, and the information gathered was used to identify key issues and concerns raised by the local community and how those issues could be tackled during the project.

To involve the local community, mark the beginning of the tunnelling process, and the arrival of the TBM, Farrans and Joseph Gallagher ran a competition to name the TBM. This was won by a local girl called Penelope who attended the event with her family, naming the TBM after herself as it was ‘strong, like her.’ Farrans and Joseph Gallagher also asked the community to nominate a local charity that would receive a £1000 donation to mark the project milestone. The Great North Air Ambulance received the most votes and attended the event on the day.

[caption id="attachment_14144" align="alignnone" width="1200"] (left) Penelope named the TBM after herself and (right) £1000 donation to Great North Air Ambulance - Courtesy of Farrans Construction[/caption]

Farrans are also involved in educational engagement by joining in with established local programs such as the ‘Start Small, Dream Big’ school initiative, run by the North East Local Enterprise Partnership. The scheme is a national DfE funded pilot aimed at raising aspirations, challenging stereotypes, and helping children connect with the world around them.

Farrans took part by running several STEM workshops, with local children taking part in exercises to design and build water filters, in the context of surviving a ‘Zombie Apocalypse’. In doing so, they learnt about the work Farrans is doing for Northumbrian Water in delivering the Tees Pipeline, as well as the importance of transferable skills and the diversity of roles within the construction and civil engineering sector.

Stakeholder engagement (farmers and landowners)

Northumbrian Water appointed a land agent to streamline the engagement of landowners and farmers along the pipeline route who would be impacted by the works. The land agent, Bell Ingram, conducted detailed conversations that began during pre-construction, and have continued throughout the project. This liaison has ensured that key stakeholders are kept fully informed of the progress of the works and any potential impacts it may have on them, including pre-construction investigation, access, and post-construction drainage designs.

Conclusion

Despite some of the technical challenges and ongoing poor weather conditions faced during construction, the project is progressing generally to programme. By July 2024 the Tees tunnel had been completed and approximately 20km of cross-country pipeline had been laid. Proactive stakeholder engagement has contributed significantly to the ongoing success of the project, with positive engagement with landowners and farmers being particularly noteworthy.

The project is on schedule to deliver water into service in early 2025, with reinstatement works to be completed by August 2025.

With approximately 60km of new 800/900mm pipeline required to replace the existing potable water mains, some of which are over 150 years old, the Tees and Central Strategic Pipeline will directly improve water quality, network resilience and operability within the Tees Network. The pipeline will serve approximately 50,000 properties and link a number of strategic assets serving the Barnard Castle, Darlington and Teesside conurbations, providing significant resilience to the overall system by 2028. The scheme will provide strategic connections between Lartington Water Treatment Works (WTW) and the existing service reservoirs (SRs) at Whorley, Shildon, Beaumont Hill and Long Newton. The works are being phased over two AMP cycles with Phase 1 currently under construction and Phase 2 in the definition stage. The scheme forms part of NWG’s wider Tees Network Strategy with further improvements to follow. Project organisation Northumbrian Water Group’s (NWG) framework technical design and design and construction delivery partners, Mott MacDonald, Stantec UK, Mott MacDonald Bentley and Esh-Stantec, are working together as part of a collaborative team called IDeA (Integrated Delivery Alliance) to deliver a major infrastructure project spanning across Darlington and County Durham. A key focus throughout the multi-disciplinary project has been effective collaboration which has been aided by involvement from specialist companies such as Lichfields and Bell Ingram. Figure 1 (below) shows the project organogram for this project. The delivery methodology, design, and construction principles have been developed jointly by all parties in the IDeA team. There have also been opportunities for carbon reduction by using low carbon water and a carefully considered material selection methodology. [caption id="" align="alignnone" width="1200"] Figure 1: Project team organogram - Courtesy of IDeA[/caption] Project scope In addition to the new pipeline, the scheme also involves the decommissioning and abandonment of over 80km of ageing pipeline as well as other assets including pipe bridges and booster pumping stations. To facilitate the abandonment of these assets, existing local networks will ultimately be connected to a combination of new or re-purposed pipelines, ensuring approximately 16,000 properties between central Darlington and Winston village to the west are among those that will benefit from the investment. Carbon reduction Carbon quantification has been an important part of the scheme in order to align with the transition towards a net zero carbon economy, and every attempt has been made to ensure the design solutions are not only hydraulically sound, but that carbon as well as total expenditure is reduced. NWG’s customers in this area are predominantly supplied from two water treatment works, depending upon prevailing supply and demand conditions: Lartington WTW: Source water is delivered under gravity into the water treatment works from upland impounding reservoirs and supplied into the potable water transmission network also via gravity. Broken Scar WTW: Source water is pumped from the River Tees into the works, treated and further pumped into the potable water transmission network. Potable water supplied from Lartington WTW is therefore more energy efficient and the construction of the new pipeline allows NWG to maximise this more cost-efficient water by delivering it into key locations of the potable water supply network in lieu of water from Broken Scar WTW, which may have passed through up to three water pumping stations. Typically, this will mean energy savings on the production and distribution of up to 30 Ml/d of potable water. [caption id="" align="alignnone" width="1200"] Figure 2: Overall pipeline schematic - Courtesy of IDeA[/caption] Design collaboration To deliver technical excellence, the project team has worked closely with NWG’s network operatives, controllers, and analysts to help them enhance their network control and to provide future planning for resilience. Extensive hydraulic modelling and scenario planning has been undertaken to ensure the network is robust, can meet requirements to support other areas of the system to the north and east of the new strategic network, as well as meet future aspirations for enhancements in the downstream network. Peer reviews of all design aspects is a continuous process on this project, utilising technical expertise from all parties. Design reviews are scheduled weekly to engage with NWG’s wider project team as well as internally within the IDeA team, meaning there is early challenge of key design aspects and collaboration to innovate and use best practice on technical issues. IDeA have been appointed as Principal Designer to ensure that CDM 2015 (Construction Design & Management Regulations 2015) is adhered too. IDeA has used the reach-back into their two parent organisations to maximise innovation, technical best practice, and the use of digital tools to assist in optimisation of the alignment, carbon assessment and delivery of the common data environment (CDE). ArcGIS online ArcGIS has been used as a CDE for this project to ensure the project team has a single source of information for making and recording design decisions. This software application was selected due its visual, interactive and geospatial environment. Geo-environmental constraints mapping, aerial photogrammetry, route alignments, utilities, local development information, hazards and design decisions are all recorded within the CDE allowing various data sets to be displayed across several geospatial maps. Alignment adjustments made within the CDE are immediately shared with the rest of the project team ensuring the team has access to information that is up to date, accurate and relevant. This CDE was also used to host the data for tenderers for Phase 1 to ensure they were provided with a common platform of information, see Figure 3 (below). [caption id="" align="alignnone" width="1200"] Figure 3: Phase 1 ArcGIS online tender package - Courtesy of IDeA[/caption] Stakeholder engagement Engaging and communicating with stakeholders at the earliest opportunity has been critical to moving the project forward. IDeA and NWG’s communications team have worked together to ensure a wide range of stakeholders have had early sight of the project including local MPs, affected councils, Environment Agency and local wildlife trusts, with letter drops and planning consultation drop-ins. IDeA has worked alongside Bell Ingram and NWG’s Estates team, to deliver early consultation and land entry notices to over 150 different landowners and their tenants impacted by the pipeline route and the significant associated site investigation works. These have included environmental/ecological surveys, ground investigation, geophysical surveys, and archaeological trial trenching. This collaboration is continuing throughout the concept design and definition stage of Phase 2 of the project. The outputs from the CDE have enhanced stakeholder engagement, allowing stakeholders to understand the scale of the project and the full constraints requiring the chosen alignment. The CDE has also been used to assist with the creation and management of land entry notices across the full scheme. Health, safety and environment There has been an extensive hazard logging process during the project concept and definition phases, using data sources such as NWG’s GIS system and from utility companies. Hazards in the vicinity of proposed works have been logged within the CDE, assigned a risk significance, and then fed into design decisions across the scheme; this process has been made more collaborative and visible by using CDE and easier to pass on into the detailed design and construction phases, see Figure 4 (below). [caption id="" align="alignnone" width="1200"] Figure 4: Hazards recorded and managed within a geospatial CDE - Courtesy of IDeA[/caption] Planning and environmental impact assessment Due to the scale of the works, planning permission is required for both phases of the main pipeline alongside an Environmental Impact Assessment (EIA). This work has required collaboration between the design teams, construction experts, the environmental and geotechnical teams and NWG’s planning consultants, Lichfields. The CDE has been used to collate the information for the EIA and has been instrumental in providing a visual platform to assist the team in defining the red line boundary to meet the requirements for the construction of the works, including working areas, access points, site laydown area and compounds. Planning permission has been granted for Phase 1 and is in process for Phase 2. The planning documentation for Phase 2 is anticipated to be ready for submission in Q1 2024. Design principles and key design aspects To optimise the pipeline route, a number of guiding design principles have been utilised including keeping the route as short as possible, keeping a uniform gradient fall in the vertical alignment, maintaining the pipeline below the hydraulic grade-line and favouring curvature over formed bends to reduce headloss. Geo-environmental impacts have been minimised by avoiding areas of significant ecological or archaeological importance and avoiding high risk ground conditions and potential ground or groundwater contamination. The route alignment has also been developed carefully considering landowner and customer impacts. Early engagement of material suppliers, ground investigation teams, early contractor engagement, and working closely with the environmental team has allowed IDeA to optimise the pipeline design and flag any potential hazards so design adjustments can be made with relative ease. Lessons learnt from Phase 1 are being used for efficiency and best practice in design and specifications for Phase 2. Steel was selected as the pipeline material via material selection matrix with input from suppliers, installers, world renowned technical specialists, NWG operational experience, as well as geotechnical, carbon and civil teams. [caption id="" align="alignnone" width="1200"] Delivery of steel pipes to the site and (inset) pipes arriving in the UK - Courtesy of FT Pipeline Systems[/caption] Tees & Central Strategic Pipeline: Supply chain - key participants Design - pipeline & tunnels: Mott MacDonald Design - pipeline & strategic connections: Stantec UK Planning consultants: Lichfields EIA: Mott MacDonald Land management consultant: Bell Ingram Land drainage design: Land Drainage Consultancy Ltd Design & construction: Farrans Construction Lead designer for Farrans: Atkins Tunnel design & construction subcontractors: Joseph Gallagher Ltd Pipe laying & associated welding: Grant Plant Hire Ltd Slide rail shoring: National Trench Safety UK Steel pipes: FT Pipeline Systems Pipe fittings: George Green (Keighley) Ltd Shaft segments: Macrete (Ireland) Ltd Tunnel precast pipes: FP McCann Strategic crossings and connections Strategic crossings and connections have all been identified, developed, reviewed, and enhanced with input from stakeholders from both NWG and IDeA through formalised design sprints, meetings and workshops. Resilience has been considered at every strategic crossing taking consideration of future maintenance access and redundancy of the system as a whole. Crossings and tunnels There are various major road crossings including the A1(M), three river crossings and two railway crossings. To determine the most suitable method of strategic crossing, all significant environmental, geotechnical and civil constraints have been carefully considered, with options being the subject of stakeholder review meetings. As a result of these discussions, tunnels have been proposed for one major road crossing, one river crossing and both railway crossings. The tunnels are all proposed at 1.8m diameter and will contain twin pipes of 700mm diameter. Lengths range from 60m to 250m and depths from 8m to 50m. The remaining major road crossings will be open cut. The two river crossings are to be traversed by pipe bridges both approximately 25m in length. [caption id="" align="alignnone" width="1200"] Tunnel shaft at the River Tees crossing - Courtesy of Mott MacDonald[/caption] Strategic connections into service reservoirs Five service reservoir strategic connections are required to deliver this project, one at the WTW and the others to SRs, with the end result giving enhanced resilience and operability to the pipeline and network as a whole. Significant consideration and collaboration with NWG stakeholders has been undertaken for each connection to de-risk construction operations and avoid interruption to supply to a significant number of customers. New flow meters, turbidity monitoring and control valves will be installed on these connections to provide further monitoring and control, enabling more flexibility in control of the system and improve water quality and efficient movement of supply throughout the network, maximising operating efficiencies. Reconnecting district metered areas Due to the extensive abandonment of pipework required, 20 district metered areas (DMAs) (approximately 16,000 properties) require re-connection to an alternative water supply. The DMA works use a combination of re-purposing existing mains, laying new mains and abandoning pumped supplies in favour of pressure-managed gravity solutions. DMA enabling works were discussed as part of the early engagement with NWG including flow reversal, flushing and conditioning. A key priority in these discussions has been the commissioning and decommissioning sequence of individual elements of the reconnection works to ensure minimum customer and operational impact. Asset abandonment and decommissioning As for the reconnection works, the abandonment works could have significant customer impact without proper consideration of sequencing and significant collaboration with NWG operational staff. The abandonment works will be sequenced to suit the commissioning of the pipeline in Phase 1, the Phase 2 pipeline and the reconnection works in Darlington and the surrounding area. The abandonment works will require a number of interfaces with the existing network requiring double isolation, thrust restraints, asset removal and trunk main drain-down and de-chlorination. Consideration is also being made to the reduction in resilience in the hydraulic network once abandonment has taken place, with contingencies being developed so that reconnected DMAs can still be reliably supplied. [caption id="" align="alignnone" width="1200"] FP McCann jacking pipes - Courtesy of Mott MacDonald[/caption] Conclusion At the time of writing (July 2023), Phase 1 of the project is under construction by Farrans Construction and the pipeline is expected to be in service by March 2025. The Phase 2 planning submission is anticipated to be made in Q1 2024, with detailed design and construction works starting in 2025. Lessons learnt from Phase 1 during the detailed design and construction phases will be used for efficiency and best practice in Phase 2. The collaborative environment created by the project team and use of ArcGIS as the CDE have enabled this project with multiple stakeholder interfaces to be delivered to efficiently and effectively. Where possible, the IDeA team involved in Phase 1 of the scheme have continued to support NWG in detailed design and construction and continued into development of the Phase 2 concept and design to retain project experience and carry lessons learnt forward throughout the project’s lifespan.