Supply Chain - Stormwater Storage - Storage Tunnels

The Southampton Shellfish Scheme comprises the upgrade to four wastewater treatment works and one combined storm overflow (CSO) discharging effluents to the Solent. The Water Industry National Environment Programme (WINEP) No Deterioration Shellfish Drivers (ND_SW) have dual targets: (i) to reduce the number of intermittent storm discharges to 10 significant spills or less per year (as a 10-year average) for the agglomeration of assets impacting Southampton Shellfish Water, and (ii) for the final effluent discharges, achieve a 6.6 log reduction in E. coli between crude sewage and the boundary of Southampton Shellfish Water. Additionally, WINEP U_IMP5 drivers resulting in an increase in flow to full treatment (FFT) were applicable at some of the sites, therefore design and construction for all drivers were combined under the same project. Site Pre-U_IMP5 initial calculated volumes (m3) Post Post U_IMP5 impact to agglomeration (June 2021) (m3) Final Volumes (m3) Millbrook WwTW Yes Yes Yes Slowhill Copse WwTW Yes Yes Yes Woolston WwTW Yes No No * Ashlett Creek WwTW Yes No Yes Ensign Park CSO Yes No No Table 1: Southampton Shellfish Scheme drivers * N/A, but FFT is being increased as a mitigation for ND_SW driver Southampton Shellfish Scheme sites

The technical solutions considered during design included increasing the storm tank capacity and the hydraulic capacity of the wastewater treatment works (WwTW) to reduce the intermittent storm discharges, with UV irradiation or membranes being considered to achieve the disinfection requirements.

[caption id="attachment_14597" align="alignnone" width="1200"] UV irradiation system at Slowhill Copse WwTW (December 2023) - Courtesy of Southern Water[/caption]

Details of the five sites are as follows:

Millbrook WwTW treats for a population equivalent (PE) of 147,000 with biological treatment provided using a 4-stage Bardenpho Activated Sludge Process (ASP). Slowhill Copse WwTW treats for a PE of 77,000 PE and provides biological treatment via a Modified Ludzack-Ettinger (MLE) configured ASP. Woolston WwTW treats for a PE of 70,000 and has an MLE configured membrane bio-reactor (MBR). Ashlett Creek WwTW treats for a PE of 15,000 and provides biological treatment via a sequential batch reactor (SBR). Ensign Park is a combined sewer overflow (CSO). Modelling & optimisation of storm volumes

The project drivers required a reduction of spill frequency at storm overflows for all the catchments that discharge into Southampton Shellfish Water. This impacted five separate wastewater treatment works catchments.

Early in the design, the Southern Water (SW) project team identified an efficiency opportunity of combining the FFT U_IMP5 (increase in flow to full treatment) Driver with the Shellfish Driver, which had a significant impact on reducing the volume of the storm storage tanks. SW held regular meetings and agreed the approach with the Environment Agency (EA) including alignment of Regulatory output dates to the end of the AMP period.

The assessment of storm storage is based on the agglomeration approach outlined in the EA PR19 shellfish guidance and methodology. The definition of a significant spill was agreed with the EA at the conceptual stage of the scheme. This assessment treated all the discharges as a single agglomeration.

[caption id="attachment_14601" align="alignnone" width="1200"] UV irradiation system at Millbrook (May 2023) - Courtesy of Southern Water[/caption]

In summary, the integrated combined driver approach provided the following benefits:

Avoided abortive investment: Storm tanks for ND_SW being oversized (increased FFT from U_IMP5 reducing storm flows). UV irradiation system and associated feed pumping for ND_SW being undersized (increased FFT from U_IMP5). Reduced carbon impact: By avoiding assets no longer required. By avoiding an inefficient 2-stage construction approach. Avoided potential abortive third party land acquisition and development. Reduced construction, traffic movements and the impact to the local community, particularly within the urban areas. Avoided unnecessary impact to the environment and ecology. Avoided potential abortive works for 3rd party infrastructure (for example, power upgrades).

To develop the solutions required at each wastewater treatment works, the sewer network performance for the five catchments was designed using a 10-year rainfall dataset. The observed spill frequencies across the catchment had to be agglomerated to ensure that 10 significant spills or less per year was achieved over a long-term (10 year) average.

This meant the modelling was more complex and took a lot longer than a usual model build and verification exercise because of the need to assess all five catchments together.

Following subject matter guidance from across the industry, the project team used an innovative approach of using an extended rainfall series duration and a single rain gauge. In addition, the team targeted the storage volumes at sites where there was available capacity to arrive at the most efficient storage volumes that were significantly lower than the original estimates, all while complying with good industry practice. In summary, this included:

Extending the rainfall series for a longer period than 10 years to be more representative of long-term weather patterns, addressing extremely ‘wet’ periods within the original 10-year series. Using a single rainfall profile as this coastal rain gauge is more representative of the rainfall falling on the main urbanised sections of the catchments. An extended rainfall series to help address the annual frequency, extremeness and year-on-year variability of rainfall patterns and particularly wet or dry periods. [caption id="attachment_14602" align="alignnone" width="1200"] Storm Shaft in Ashlett Creek (June 2024) - Courtesy of Southern Water[/caption] Optimising storm storage volumes

The project team considered the best location for increasing the capacity of storm storage considering the cost/benefit for reducing significant storm spills. For example, at Millbrook WwTW redundant storm tanks were utilised that provided a volume of 3,140m3. The increase in volume at Millbrook enabled the storage volumes to be optimised across the agglomeration of sites with volumes being offset against other more constrained sites.

Southampton Shellfish Scheme: Supply chain - key participants Client: Southern Water Delivery partners & outline/detailed design: GTB Galliford Try Binnies UV design & coastal & network modelling: Stantec UK Coastal & network modelling: Southern Water Civils & pipework: Knights Brown Civils & pipework: Impact Formwork Storm shafts & tunnelling: HB Tunnelling Piling works (Woolston WwTW): Rock & Alluvium Piling works (Woolston WwTW): Keller Foundations Storm tank remedials: Concrete Repairs Ltd Mechanical installation: Bridges Electrical Engineers Ltd Mechanical installation: Steelway Electrical installation: Field Systems Design Electrical installation: Loxton Electrical ICA: Total Automation & Power (TAP) MCCs: MCS Control Systems GRP kiosks: Industrial GRP Ltd Penstocks: Ham Baker UV: Trojan Technologies Membranes: Koch (KMS) [caption id="attachment_14599" align="alignnone" width="1200"] Refurbishment of redundant storm tanks at Millbrook to provide 3,400m3 capacity - Courtesy of Southern Water[/caption] Infiltration - optioneering To optimise the significant storage volumes at the works, sustainable catchment opportunities were considered for the large, urbanised Millbrook and Woolston catchments by the removal of specific areas of groundwater infiltration and surface water from foul sewers. The optioneering was undertaken using an optimisation software package to target impermeable areas (roads and roofs) connected to the network and working through simulations (up to 20,000) to assess parts of the catchment where connected roads and roofs could be removed from the foul sewer. The benefit was not as expected when considering the agglomerations due to spills from the other assets. In addition, the timescale to achieve long-term reduction from impermeable area removed or groundwater infiltration would require a multiple AMP period. Future opportunities using the optimisation techniques will be considered for similar CSO and storm spill frequency schemes to achieve sustainable catchment opportunities, by the removal of specific areas of groundwater infiltration and surface water from foul sewers. Woolston WwTW - increasing FFT

The initial significant storm volumes at Woolston were extremely challenging given the location of the site within an urban environment and lack of available space. The project team identified an opportunity of increasing the FFT at Woolston, which provided a significant reduction in storage. The scope involved utilising hydraulic headroom within the works, and through the installation of additional MBR capacity and associated pump upgrades, enabled a 20% increase in FFT at Woolston WwTW (427 l/s to 534 l/s).

[caption id="attachment_14603" align="alignnone" width="1200"] Construction of the shaft at Woolston - Courtesy of Southern Water[/caption]

The programme to deliver the increase in FFT at Woolston was short and provided an early reduction in E. coli concentration discharging to the Solent. This early delivery reduced 20% of the total E. coli concentration across the agglomeration of sites and was fundamental in agreeing new regulatory dates for the SW_ND (storm storage) drivers. The combination of the integrated driver approach to reducing spills, the innovative modelling and optimisation of assets reduced storage volumes by circa 46,000m3.

The final volumes are as shown in Table 2:

Site Initial calculated volumes (m3) (pre-U_IMP5) Post Post U_IMP5 impact to agglomeration (June 2021) (m3) Final Volumes (m3) Millbrook WwTW 3,684 200 3,400 Slowhill Copse WwTW 13,678 2,000 2,000 Ashlett Creek WwTW 4,176 1,650 1,650 Woolston WwTW 27,422 13,120 5,000 Ensign Park CSO 3,806 280 280 Blechynden Terrace CSO 5,000 0 * 0 * Newtown CSO 562 0 * 0 * Table 2: Southampton Shellfish Scheme storm storage volumes * Reduction driven by reduced spills in the agglomeration New final effluent disinfection at Slowhill & Millbrook WwTWs (AMP7 & AMP8):

In response to a number of drivers, the EA has recently revised its approach to design and permitting of UV irradiation systems for the disinfection of final effluent. The aim is to move away from the use of generic assumptions, to follow international best practise with an approach which employs the use of a site-specific data in conjunction with performance validated UV irradiation equipment. This revised approach enables development of a significantly better understanding of performance and limitations on a site-specific basis.

Understanding the variation and impact of key wastewater characteristics on parameters such as UV transmittance and the UV dose-response relationship enables selection of a representative design envelope and minimum target UV dose. This enables the capital solution to be optimised, minimises power usage, operational costs and carbon impact while securing environmental performance.

[caption id="attachment_14609" align="alignnone" width="1200"] UV irradiation system at Millbrook (June 2024) post commissioning/FST under construction and (inset) UV irradiation system at Slowhill Copse WwTW - Courtesy of Southern Water[/caption]

The steps undertaken for the development of the design parameters and permit conditions for the UV irradiation systems at Slowhill and Millbrook WwTWs can be summarised as follows:

Coastal/estuary modelling was used to determine the dilution/dispersion factor available from the effluent discharge location to the Shellfish Water boundary. The boundary is due to extend closer to the discharge points in AMP8 (i.e. reducing the available dilution of the final effluent discharges), therefore disinfection targets were evaluated for both AMP7 and AMP8 during design. This enabled the overall system (channels, MCC and power requirements) to be designed with the ability to install the equipment required in AMP7 and accommodate further banks to meet the lower E. coli targets required to avoid abortive and/or extensive additional construction in AMP8. A programme of sampling and analysis was carried out (from April 2020 to May 2021) to collect data on the variation of microbial and sanitary characteristics of the final effluent. The results were compared to the parameters available from historical site data in order to ensure that the sampling was representative of the expected range. Variation in UV transmittance was recorded using online instruments for assessment with flow data to understand their relationship. The UV dose-response relationship for E. coli for the final effluent was developed using collimated beam testwork to determine the target UV dose required to achieve the disinfection targets for permitting for both AMP7 and AMP8. The data was used to develop a range of design parameters that were then used in conjunction with UV suppliers’ performance validation information to determine a range of UV irradiation system configurations. The options were evaluated considering the different levels of resilience, redundancy and risk of non-compliance with the EA’s proposed new permit conditions.

The new UV irradiation systems have been in operation at both sites since Autumn 2023 and are consistently achieving concentrations of E. coli in the final effluent discharges that will maintain the concentration at the Shellfish Water Boundary below the post PR19 target value of 5 cfu/100ml as a geomean.

[caption id="attachment_14600" align="alignnone" width="1200"] (left) Millbrook UV pumping station and (right) MBR cassette capacity being increased in Woolston WwTW - Courtesy of Southern Water[/caption] Woolston WwTW - working with care

Due to the limited availability of operational land in Woolston, the new storm shaft is being constructed beneath a car park and green area own by Southampton City Council (SCC), the area also had a Multi-Use Games Area (MUGA). The project team and the representatives of the Council engaged in extensive discussions prior to submission of the planning application which ensured a positive outcome for both parties.

From those conversations the project team learnt that the Council had worked to create a low nutrient coastal grass environment in the zone affected by the project. The topsoil had been amended and sown with the current species in previous seasons. Therefore, the agreed approach was to retain the topsoil stored on site and reinstate it at the end of the project, enabling the green area to grow and cover the old disused carpark.

The first activity after site mobilisation was relocating the reptiles that naturally inhabit coastal grass biomes. All areas with long grass that were part of the construction compound had the grass cut in two passes to encourage reptiles to move to nearby unaffected zones. Additionally, the top 100mm of soil was hand excavated with an ecologist carefully moving those reptiles still on site.

SW, working closely with the local Council, has ensured that the pre-existing facilities not only are kept despite the new structures being built, but that they are also improved. The number of parking bays and EV charging points will be maintained with improved access arrangements to avoid unwanted camping vans. The MUGA will be improved so the excessive slope that the old court had is removed and the pedestrian access to an adjacent park is protected with bollards, as previously vans used to park using part of the footpath.

[caption id="attachment_14596" align="alignnone" width="1200"] Landscaping over Woolston storm shaft - Courtesy of Southern Water[/caption] Progress to date, successes and future phases

The storm tank at Millbrook WwTW and the increase in flow to treatment at Woolston WwTW were both commissioned in July 2022 while the projects to install UV irradiation at Slowhill and Millbrook WwTWs were commissioned in Autumn 2023. In combination, these improvements represent a reduction of 72,500 cfu/s of E. coli being discharged to the Southampton Shellfish Waters, which is more than 60% of the total E. coli concentration reduction when all the projects are completed.

Results from sampling carried out after commissioning have demonstrated that both UV irradiation systems at Slowhill and Millbrook have reliably achieved the target efficacy, with concentrations of E. coli in the effluent post disinfection regularly below 200 cfu/100ml. Additionally, concentrations of E. coli in the final effluent discharge from Woolston have been consistently below 35 cfu/100ml since July 2019, following commissioning of the MBR.

The next key milestones are 31 December 2024, when the new storm tank at Ashlett Creek WwTW will be commissioned, and 31 March 2025, when all the remaining storage and increase in flow to treatment drivers will be completed.

The Thames Tideway Tunnel project is a 25 km (16 mile) combined sewer under construction under the tidal section (estuary) of the River Thames as it runs through London. It will significantly increase the capacity of London’s sewerage system, large sections of which were built in the 19th century, and be able to capture, store and convey almost all of the raw sewage and rainwater that currently overflows into the Thames Estuary. The Tideway tunnel will connect 34 of the capital’s most polluting combined sewer overflows (CSOs), transferring the foul water to the Lee Tunnel for onward delivery to Beckton Sewage Treatment Works. The completion of the Thames Tideway Tunnel scheme, currently anticipated for 2025, will significantly improve water quality, capturing more than 95% of the spills that currently enter the river to the benefit of London’s almost 9 million residents. Location

As part of works on the Central section of the Thames Tideway Tunnel scheme, Barhale was contracted by the Ferrovial and Laing O’Rourke joint venture (FLO JV), the lead contractor for the central section of the project, to deliver the heavy civils and civils structures that would intercept the sewage overflows and transfer these to the main Tideway tunnel beneath the river Thames.

The Victoria Embankment site was located in the City of Westminster, on the north side of the river Thames adjacent to, and south-west of, the Hungerford Bridge and Golden Jubilee footbridges. The site was bounded to the south-east by the River Thames and the north-west by the A3211, beyond which are the Victoria Embankment Gardens.

[caption id="attachment_10008" align="alignnone" width="1200"] (left) Works within the cofferdam in the Thames and (right) works ongoing within the cofferdam - Courtesy of Barhale[/caption] Scope of work

The works were delivered in stages to provide protection to existing assets and engineering control over the structure’s movement. One of the first elements of work undertaken at Victoria Embankment was the construction of a 50m long secant piled wall that would retain and minimise ground movement on the dual carriage way and the Circle and District tube lines.

The next stage of the works comprised the diversion of the existing gas mains and the completion of the cofferdam. Once these were completed, piling operations could start. In total, 117 piles were installed: 47 (No.) 600mm bearing piles for the CSO structure and 70 (No.) 1200mm piles for the new river wall. These were required to provide adequate bearing capacity for the future structures.

The groundwater levels along the Tideway Central route, including Victoria Embankment, did not allow safe excavation of the shafts and tunnels and required the project team’s attention. A temporary works assessment was carried out along the route and verified by using pump tests, which modelled the required pumping capacity to dewater the existing aquifers.

At Victoria Embankment, Barhale installed four 106m deep Chalk Wells, six 65m deep Thanet Sand Wells, and six 50m deep Lambeth Group Wells. This system was also accompanied by in-shaft and tunnel wells that have targeted local pockets of water.

The 15m diameter shaft was built using three techniques. For the first 14m, the shaft was sunk using the caisson method and precast segments. This method was chosen for this section due to the granular material that was reported in the existing boreholes.

[caption id="attachment_10006" align="alignnone" width="1200"] Secondary lining works - Courtesy of Barhale[/caption]

Once past this layer, London Clay was encountered, and the excavation method was changed to underpinning. This method was used for excavating down to 32m below ground level. Due to the limitations of precast segments, the lining technology was changed to sprayed steel fibre reinforced concrete with a thickness of 600mm. This method allowed for better control of shaft profiles and portals for future works.

At formation level, a 2m deep reinforced concrete base slab was cast. The construction of this base slab required approximately 80 tonnes of steel and over 450m3 of high GGBS (ground granulated blast-furnace slag) concrete.

From this level a series of temporary works were implemented to allow the short connection tunnel to be excavated and supported using SCL (sprayed concrete lining). The connection tunnel is 18m long and varied in shape. During the first 14m, the tunnel internal diameter (ID) is 3.6m and in the last 4.5m the tunnel transitions to an ID of 4.9m.

The completion of the SCL works allowed for the site to transition to the full civils stage and start the works on the shaft and tunnel secondary lining and internal structures. Above ground level works that were released by the achievement of this milestone comprised the construction of new chambers that will deal with the intercepted flow and the new river wall that encompasses these structures and protects them from possible ship impact.

For these works at Victoria Embankment, Barhale used approximately 1400T of rebar and over 7000m3 of low carbon emission concrete, making this one of the bigger schemes that has been delivered during the Thames Tideway Tunnel project.

Tideway Central: Victoria Embankment: Supply Chain - key participants Main designer & contractor: FLO JV Ferrovial Laing O’Rourke Delivery contractor: Barhale RC piling: Expanded Piling Dewatering: WJ Groundwater Civils works: Flatley Construction Sawcutting/drilling: EDD (Euro Diamond Drilling) Ltd Waterproofing: Renesco Temporary electrical set-up: Select Site Solutions Concrete supplier: CEMEX UK Concrete supplier: Hanson UK Additives for SCL works: Normet Waterproofing: Sika Steel supplier: Express Reinforcements Ltd Steel supplier: HY-TEN Ltd Plant supplier: Select Cranes Plant supplier: Flannery Plant Hire Challenging tunnel construction

The short connection tunnel at Victoria Embankment was design to be excavated and supported using the sprayed concrete lining method. This allowed for the short connection tunnel to wrap around and support the main tunnel during the break-out and final connection operation.

To put this in stages, the Victoria Embankment team was required to construct the tunnel using SCL and line the asset using cast in situ reinforced concrete and reduce its diameter to a constant 3m ID. The main tunnel team would be required to build the main tunnel using a segmental lining and cast in situ a reinforced liner, missing only the break-out area towards the Barhale connection tunnel. Once the segments were broken out, the two independent concrete structures would be joined together using cast in situ reinforced concrete.

The ground condition investigations for the connection tunnel identified a band of sand in the middle of the tunnel excavation, with a thickness of 1m and the presence of water.

On the assumption of the layer thickness and presence of water, a temporary design was progressed to support the excavation while spraying concrete. The designer prescribed the use of a pipe arch canopy support system for the narrower, 3.6m ID section of tunnel, with piles providing support for the remaining 4.9m ID section. The dewatering specialist prescribed the use of shaft wells and in-tunnel wells to allow efficient dewatering of the layer.

[caption id="attachment_10007" align="alignnone" width="1200"] (left) Commencement of shaft works, and (right) diversion works within Victoria Embankment -Courtesy of Barhale[/caption]

During the initial 3 to 4m of tunnel excavation, the face log showed an increase of the sand layer band and larger volumes of water than expected.

The sand layer covered approximately half of the excavation face at this point. As works progressed through the next 4m, additional wells continued to be drilled into the tunnel to target the water presence and the band of sand kept extending. Nine meters in, and the sand layer presence ranged from midway up to, and 3m above, the tunnel crown.

The encountered sand layer was also very fine which made spraying concrete challenging. As the concrete was sprayed, the sand bond was so small that the sprayed concrete was pilling off in small increments, making the excavation bigger. To prevent this occurrence, fast setting grout was sprayed as an initial layer and only then sprayed concrete.

This amendment to the plan did not solve the issue of the water presence and problems wet sand causes to excavations, especially tunnels.

An additional amendment to the plan had to be made. The team set out to space proof and conducted a feasibility study to understand if banker bars could be deployed. The temporary works design was then independently checked by a second design consulting company and approved by client FLO JV.

Barhale safely implemented the temporary works support, which meant installing eight advances of banker bars and spraying the primary concrete lining against them.

Works completion

The complex civils works on Victoria Embankment CSO Project to intercept the combined sewer overflows and to divert them into the Thames Tideway Tunnel presented challenging and unexpected ground conditions. Demonstrating agility and innovation, the Barhale team was able to deliver an excellent solution which both met the project timeline and provided best value for money.

The Stroud Sewerage Strategy is a major investment by Severn Trent which is required to overhaul of the existing sewer network by installing almost 3.5km of enlarged sewer pipe, separating surface water from the sewage network, creating additional storage with smart controls to hold stormwater back during large storm events before returning it to the treatment works when the rainfall has subsided, and making improvements to Stanley Downton Sewage Treatment Works. This paper follows on from the case study published in Water Projects 2022, which focussed on the design and optioneering elements of the programme of works. Scope of works The Stroud Sewerage Strategy is made up of five key elements: Trunk sewer improvements. Combined sewer overflow & storage. Surface water separation. Infiltration reduction. Stanley Downton WwTW. Construction started in March 2022 and details of the progress to date (July 2023) is covered in this case study. New trunk sewer In order to reduce the risk of sewer flooding and convey flows from the existing Wallbridge CSO, design and build contractor Galliford Try was required to design and build a second trunk sewer system, transferring flows 3.65km to the new CSO site on the outskirts of Stroud. The new sewer network will operate entirely under gravity, with no siphons and falls at a minimum gradient of 1:500. [caption id="" align="alignnone" width="1200"] (left) The launch of TBM Marvellous Mining Molly and (right) shaft with pipe jacks installed about to be benched - Courtesy of Galliford Try[/caption] Due to varying local topography and numerous obstacles along the route the team opted for a combination of open cut and pipe jack tunnelling techniques for the trunk sewer - details below. Pipe diameter : Length Details 750mm = 900m Open cut works: 2-5m deep, includes 1 x River Frome crossing 1500mm = 769m Open cut works: 3-6m deep, includes 1 x River Frome crossing 900mm = 35m TBM Marvellous Mining Molly: 1 x tunnel drive crossing under A419 1200mm = 550m TBM Lilian: 4 x tunnel drives under Dudbrige Road (dual carriageway), car parks and private land 1200mm = 650m TBM Suzanne: 6 x tunnel drives under Stroudwater Navigation Canal & major gas mains 1500mm = 591m TBM Florence: 3 x tunnel drives under A419, Stroudwater Navigation Canal & Painswick Stream BSP Consulting Ltd carried out the structural design of all 12 tunnelling shafts (varying from 3.66m, 5m and 6m in diameter), with the ring segments and cover slabs supplied by Macrete (Ireland) Ltd. BSP also undertook the design calculations and documentation required for the five tunnelled highway crossings consents (CD622) and the buried service damage assessment reports for eight key service crossings along the route (the pipeline analysis was undertaken using Oasys software). Active Tunnelling Ltd developed a bespoke tunnel boring machine setup for the 900mm micro-tunnel which involved installing an initial 600mm laser guided auger followed by a forward reaming TBM head into the auger screw. This setup avoided the need to install a 1200mm pipe which would have caused additional risk to an existing underpass in close proximity. [caption id="" align="alignnone" width="1200"] TBM Marvellous Mining Molly in position to start mining - Courtesy of Galliford Try[/caption] Stroud Sewerage Strategy: Supply chain - key participants Client: Severn Trent Design & build contractor: Galliford Try Hydraulic model: Richard Allitt Associates Principal ecologists: RammSanderson Ecology Ltd River & spillway reinstatement: Salix River and Wetland Services Silt mitigation: Frog Environmental Water vole licensing: Wildwood Ecology Land & planning Agents: Dalcour Maclaren Topographical Surveys: Geomap Ltd Ground investigation: Grange Geo Consulting Hydraulic model: Innovyze (Infoworks ICM) Physical model: Framatome BHR Group Shafts & pipejacking: Active Tunnelling Tunnel design: BSP Consulting Traffic management: Amberon Ltd Remediation & asbestos management: Churngold Construction Water main diversions: Heartland Pipelines Sewer lining: Colus Ltd Temporary PortaDams: OnSite Central Steel fabrication & penstocks: GT Fabrications Valves: AVK UK Ltd Open cut pipework: LCS Groundworks Ltd Open cut pipes: Marshalls CPM Electrical installation & MCC: Cema Ltd DI pipework: Electrosteel Castings (UK) Ltd Shaft rings & cover slabs: Macrete (Ireland) Ltd Jacking pipes: FP McCann Ltd Washwater pumps: KGN Pillinger Lifting equipment: T Allen Engineering Services Submersible pumps: Xylem Water Solutions CSO screens: Longwood Engineering Co Ltd Prefabricated chambers & backdrops: Polypipe Civils & Green Urbanisation Access covers: Steelway Brickhouse Manhole covers: Saint Gobain PAM UK Fencing & tree clearance: Landscape Maintenance Services Interception chamber Galliford Try was required to design a new interception chamber to convey all the flows of the existing Nailsworth Sewer into the new network. Working on a live network and dealing with large flow rates naturally led the team to design a prefabricated chamber to minimise the installation time. Designers from Galliford Try and Polypipe Civils & Green Urbanisation developed a solution that incorporated a permanent backdrop, temporary flume pipe and four connections (750mm, 750mm, 1200mm and 1500mm in diameter). It was built off-site in three sections and assembled on site in one day. [caption id="" align="alignnone" width="1200"] (left) Installation of prefabricated chamber within live sewer line and (right) inside the prefabricated chamber - Courtesy of Galliford Try[/caption] River Frome crossings Due to the need to retain a constant gradient, both sewer crossings under the River Frome were very shallow with very little cover to the erodible bed level. Without creating syphons, open cutting through the river was the only feasible solution. A temporary bypass channel was constructed and lined using Salix River and Wetland Services coca matting and Frog Environmental rock rolls to prevent mobilising sediment during the works. Temporary PortaDams from OnSite Central Ltd were installed to isolate a section of river. RammSanderson Ecology Ltd provided ecological support, including moving 1554 fish between dams (129 brown trout, 493 brook lamprey, 715 bullheads, 209 sticklebacks, five eels and three roach). This element of work required a huge amount of planning and permits from Galliford Try’s Environmental Team, the Environment Agency and Natural England. [caption id="" align="alignnone" width="1200"] Construction of bypass channel and (inset) installation of the temporay PortaDam from OnSite Central Ltd  - Courtesy of Galliford Try[/caption] New CSO shaft Construction of the new 25m diameter, 28m deep combined sewer overlflow shaft started in summer 2023. A detailed update will be published on WaterProjectsOnline.com later in the year. Surface water separation The 3.88 hectares of impermeable surface area being separated from the existing catchment is situated in Stroud town centre and involved designing a new 555m long, 300mm diameter, intricate surface water sewer network within the constraints of a densely built-up area to intercept flows which otherwise would have ended up in the combined network and added to the spill events in the downstream catchment. Galliford Try undertook GPR surveys and numerous trial holes to create a map of existing buried assets and plan a route for the new sewer network. To reduce service diversions to a minimum, a number of bespoke manholes were designed, and the Galliford Try team proposed relining the existing foul sewer rather than replacing it which considerably reduced disruption and construction timescales on site. Flows from the newly separated network are transferred to Stroudwater Canal via a 232m long connection across a supermarket and council car park and under an existing retaining wall. Due to the interface with the general public and potential upheaval of working in car parks, Galliford Try chose to install the 600mm diameter pipes by using a laser guided auger. In conjunction with specialist Active Tunnelling Ltd, drive and reception pits were carefully positioned within car parking bays and the route designed to minimise disruption as far as practicable. On completion of the works, all affected stakeholders were positive and complimentary over the tidiness of the work sites. [caption id="" align="alignnone" width="1200"] (left) Excavation of shaft and (right) preparations for open cut rising main installation - Courtesy of Galliford Try[/caption] Infiltration reduction To free up capacity for foul flows in the existing network, Galliford Try eliminated 3 l/s of infiltration with specialist Colus Ltd by installing 475m of liners and injecting two-part polyurethane sealant at key locations. The constant groundwater flow was caused through a combination of old cracked sewers, old brick manholes with blown mortar and badly made connections onto the existing network. Conclusion At the time of writing (July 2023), the last remaining parts of the project include modifications to the storm return pipework at Stanely Downton WwTW, and the demolition of the existing Wallbridge CSO site. These works will be undertaken upon completion and commissioning of the new assets. The whole team from engineers, design, procurement, commercial and project management working on this difficult project have pulled together to overcome numerous unforeseen physical, environmental, financial and stakeholder challenges in Stroud. The author wishes to credit everyone involved; sub-contractors, supply chain and the client for achieving what has been delivered to date.

The Thames Tideway Tunnel Project is a 25 km (16 mi) combined sewer under construction under the tidal section of the River Thames as it runs through London. It will significantly increase the capacity of London’s sewerage system (large sections of which were built in the 19th century), and be able to capture, store and convey almost all the raw sewage and rainwater that currently overflows into the Thames Estuary. The Thames Tideway Tunnel will connect 34 of the capital’s most polluting combined sewer overflows (CSOs), transferring the foul water to the Lee Tunnel for onward delivery to Beckton STW. The completion of the Thames Tideway Tunnel scheme, currently anticipated for 2025, will significantly improve water quality capturing more than 95% of the spills that currently enter the river to the benefit of London’s almost 9 million residents. Project summary and location As part of works on the west section of the Thames Tideway Tunnel scheme, Barhale was contracted by the BAM Nuttall Morgan Sindall Balfour Beatty (BMB) joint venture, to construct a series of complex underground structures that would intercept the sewage overflows from the West Putney Storm Relief Sewer for transfer to the main Tideway tunnel beneath the River Thames. The site was located in Richmond, on the south side of the River Thames between Hammersmith Bridge and Putney Bridge, and adjacent to Barn Elms Sports Centre. Scope of work The scope of works included the construction of a 35m deep x 6m internal diameter drop shaft and a 215m long x 3m outside diameter connection tunnel. Surface level works include 6m deep reinforced concrete (RC) interception chambers, an RC culvert and an RC MEICA building, comprising an electrical intake room, telemetry room and control room for system alarms and automated actuated valves installed by the lead contractor. Barhale also built an 800m long, 4m wide access road, and installed additional sections to address Environment Agency and local authority requirements relating to existing flood defences and protected trees in the proximity of the works. The drop shaft’s construction required initial and primary spray concrete lining (SCL), with a secondary cast-in-place concrete lining to encase a new 26m long x 90mm diameter stainless steel vortex drop tube pipe. The shaft was constructed using steel fibre reinforced concrete, applied by an Oruga robotic spray machine as the excavation progressed in 1.2m increments. [caption id="" align="alignnone" width="1200"] (left) Excavation at the shaft base and (right) 2.5m ID tunnel excavator machine (TEM) being lowered into drive shaft - Courtesy of Barhale[/caption] Detailed mapping and innovative control Unlike most other Tideway sites, Barn Elms is comparatively small and the connection tunnel drive through the London Clay Formation had to be delivered from a relatively narrow 6m diameter shaft. More than two months were spent preparing a plan and mapping out the tunnel drive route to ensure the team did not encounter any unexpected problems during the drive. The requirement was that the tunnel excavator machine (TEM), which needed to be compatible with 3m diameter jacking pipes, would not have been recoverable from a standard reception shaft as the connection to the main tunnel was right under the River Thames. To address this challenge, Barhale collaborated closely with Tunnel Engineering Services (UK) Ltd to design and construct a TEM whose internal parts could be dismantled, removed and re-used after the project’s completion. The new TEM was brought to site without any engineering guiding systems so the team also needed to address the question of control. Drawing on Barhale’s extensive mining experience, traditional and digital equipment was installed on the machine to control the steer, roll and the pitching degree. Digital pressure gauges were also fitted to ensure that the limit on the jacking pressure was not exceeded. The TEM was steered by four pairs of hydraulic cylinders located between the hood and the machine body. Using information available on the geometry of the TEM and the jacking pipes, plus knowledge of the maximum allowable joint deflection of the jacking pipes, it was calculated that the steering cylinder should not be opened more than 20mm when all other cylinders are fully retracted. [caption id="" align="alignnone" width="1200"] (left) Barn Elms shaft under construction and (right) the 2.5m ID tunnel excavator machine (TEM) being lowered into drive shaft - Courtesy of Barhale[/caption] The TEM roll represents the machine’s rotation about its central axis and there was a continuous tendency to clockwise or anti-clockwise spin. To overcome the issue, inclinometers and laser targets were installed within the machine and used for base readings for roll calculation. Installing the bespoke guidance equipment, and in-detail mapping of every stage of the drive, ensured that the TEM was able to operate effectively and carry out the pipe jack successfully. A further challenge was the safe handling and maintenance of the 14 tonne, 3m diameter precast concrete jacking pipes. To address the issue, Barhale purchased a 20 tonne SWL welding roller to be used as a base stand so that the pipes could be rotated 360°. This solution enabled the team to inspect each pipe thoroughly without the need for access equipment and working at height. It also brought a huge benefit in the preparation of the inter-jack stations. Using this system, the inter-jack hydraulic cylinders could be installed around the circumference of the jacking pipes by the fitters from standing position. Overall, the use of the welding rollers saved the Barhale team time, eliminated the risk of working at heights, and reduced the number of lifting operations. This idea was nominated for a Tideway RightWay award. Barn Elms CSO Connection Tunnel: Supply chain - key participants Main designer & contractor: BMB JV Delivery contractor: Barhale Reinforced concrete works/formwork: Flatley Construction Secondary lining shuttering: EFCO UK Spray concrete lining: Shotcrete Services Ltd Steel fibre reinforced concrete: CEMEX UK Tunnel boring machine: Tunnel Engineering Services (UK) Ltd Precast jacking pipe segments: Macrete (Ireland) Ltd Stainless steel vortex generator: BMB JV Stainless steel vortex drop tube pipe: BMB JV Precast concrete cover slabs/planks: Barhale Ventilation/odour control: Specialist Plant Associates Demolition robot: Brokk Global Robotic concrete spray machine: MEYCO Oruga [caption id="" align="alignnone" width="1200"] Shaft cover slab under construction - Courtesy of Barhale[/caption] Challenging tunnel construction The tunnel was constructed using a pipe jacking technique in which the TEM was attached to a muck conveyor. The pipes were jacked continuously from the drive shaft as the excavation of the tunnel face progressed. This was a relatively large pipe and the team encountered a significant challenge about 30m into the pipe jack when small cracks were identified in nine of the eleven pipes that had been installed. The defective sections needed to be replaced. The two un-cracked pipe sections were at the rear of the pipe jack and had not entered the ground so were relatively easily removed, however, it remained necessary to remove the other nine sections. This would only be possible by breaking out the pipe sections. A recovery strategy was developed which was centred on the fabrication of a bespoke shield which could be jacked along the line of the existing cracked pipes. A special hood was devised which, as the shield moved forward, would pass above the damaged sections providing support to the tunnel roof. It would protect the workforce and equipment and allow work on the removal of the pipe sections to begin. A further consideration was that damage to the original concrete lead pipe meant it could no longer be used. It would have taken too long to recast a new concrete section so the steel shield was also designed so that it could be jacked in and used as a replacement. To start the recovery, each of the individual damaged concrete pipe sections was circumferentially and longitudinally cut into small sections. The breaking out was carried out by a Brokk demolition robot which moved down the existing pipework ahead of the shield. [caption id="" align="alignnone" width="1200"] (left) The probe drill in use, forward probing of the tunnel face before full excavation as part of the WPP and (right) temporary support from within the sacrificial outer skin of the TEM once the tunnel drive was completed - Courtesy of Barhale[/caption] Once each concrete section had been broken out, the Barhale team could move in and pull the concrete from the invert back to the pit bottom for removal. Positioning the Brokk in advance of the shield meant that the removal of the material was not impeded. Proceeding section by section, it took two and a half weeks to reach the TEM. Removal of the damaged lead pipe revealed that, under the pressure of sitting stationary in the ground for five months while the recovery strategy was devised and implemented, the tail skin of the machine had deformed more than anticipated. By restarting and moving the TEM followed by the recovery shield forward into virgin ground, the Barhale team was able to relieve the pressure on the tail skin. This permitted the removal of the hood and the docking of the steel lead pipe after which the drive could be restarted. Replacing the damaged reinforced concrete pipes created quite a challenge, but with the support of the project team, a pioneering solution to change the cracked pipes was developed. The recovery shield that Barhale developed not only enabled the damaged tunnel to be replaced but also enabled access to the TEM face where repairs and enhancements had to be conducted. Additionally, the purpose made tunnel shield was designed to allow complete dismantling upon completion of the tunnel drive, allowing the final connection to the main tunnel. Secondary lining The pipe jack was followed by a cast-in-place secondary liner to the pipe jack tunnel. Barhale worked with suppliers to design and procure an automated tunnel liner system that significantly improved the quality of the tunnel secondary liner. [caption id="" align="alignnone" width="1200"] Secondary lining shutter in place within the sacrificial TEM outer skin at the junction of the main Tideway central tunnel - Courtesy of Barhale[/caption] This consisted of a specialist automated tunnel formwork system that would ensure the tunnel secondary lining was constructed efficiently by pouring each section in one pass. This improved quality by reducing the number of construction joints compared to more traditional methods. As the equipment is fully automated, the hydraulic stop ends ensure a robust seal when pumping concrete. A mechanical travel system enabled quick set-up for each subsequent pour with minimal resources and it removed the need to manually strike and reconstruct formwork for each section of the lining. Designed for life The client required 120-year design life for the precast concrete jacking pipes. To achieve this, Barhale’s engineers worked closely with the client’s designer, materials engineers and precast experts to develop a detailed quality assurance system that included concrete mix trials and quality audits at our supplier’s facility. In addition, Barhale implemented a stringent quality control regime that covered the pre- and post-pouring of the pipes, curing, handling and transportation of the pipes. Carrying out the works required excellent stakeholder management throughout. Heavy plant deliveries were required to fall within stringent Tideway traffic management plans. Thorough planning and consultation with the supply chain, client representatives and third party stakeholders were also key for excellent HSE performance. Barhale supported BMB with meetings and workshops with asset protection teams, Thames Water, the Environmental Agency, the local authority and local council groups. [caption id="" align="alignnone" width="1200"] Shaft cover slab under construction - Courtesy of Barhale[/caption] Peter Leyton, Construction Director for the BAM Nuttall Morgan Sindall Balfour Beatty JV, praised the Barhale team for its hard work and effort in getting the TEM to the main tunnel connection:

“The resolution in the team, to come from where we were earlier and then to work through all the issues that were put in the way, is a huge testament. Also, the control of the movement in the main tunnel has been excellent and a great reflection on the efforts put in by all of the team.”