Supply Chain - Site Preparation - Scaffolding

Bourn Reservoir is an above-ground reservoir complex located approximately five miles outside Cambridge, England. Only one tank was still operational after the other two were removed from service due to natural degradation. A new tank was required to meet demand from large-scale developments in the supply area. A review was conducted to ascertain the total water volume required, revealing the need for an additional 8 ML of storage on top of the capacity of the remaining tank by the summer of 2022. Stonbury was contracted to demolish the disused circular prestressed tank in 2020, whilst the other remained in service, and in 2021, Stonbury commenced the construction of a new concrete tank next to the operational reservoir. Scope of works A summary of the works undertaken is as follows: Disconnection and demolition of the old Reservoir No 2. Ground investigation works and tree removal. Groundworks. Design of new concrete tank. Construction of new tank, drainage and connecting pipework. Installation of MEICA elements. Site description The Bourn Reservoir site is a small, spatially-constrained compound that originally contained Reservoirs 2 and 3. Land owned by the farmer adjacent to the site was utilised for the site compound which housed welfare units, a storage area, and turning space for vehicles and machinery. The land was returned after the programme was complete. [caption id="" align="alignnone" width="1200"] View of tank under construction with newly painted exterior walls - Courtesy of Stonbury[/caption] Project team The project was delivered for the client, Cambridge Water Company, by direct-delivery water sector specialist contractor, Stonbury, as principal contractor and principal designer, and Mason Clark Associates as their designer. Bourn Reservoir: Supply chain - key participants Client: Cambridge Water Company Principal contractor: Stonbury Designer: Mason Clark Associates Subcontractor: GM UK Ltd MEICA installation: IWS Mechanical & Electrical Ecological appraisal: Middlemarch Environmental Ltd Concrete delivery: Hanson UK Concrete pump hire: Camfaud Concrete Pumps Ltd Crane hire: Emerson Cranes Handrail & staircase supplier: L&G Engineering Ltd Internal steps & ladders supplier: Chemglass Access doors & hatches: Technocover Ltd Project challenges The build possessed several unique challenges due to constraints on time and space. The planning application review period was extended for further environmental assessment as part of the Tree Retention Scheme, which introduced significant time constraints to the programme. Proactive action was taken to minimise delay, and a revised foundation plan was submitted accounting for the proximity of tree roots and including provision of a perimeter root barrier trench for additional protection. Planning permission was granted in October 2021, leaving under a year to complete the project by summer 2022. Innovative pre-construction planning was required to overcome the issues posed by the constrained size of the operational area. As the site footprint dictated a tank shape that was non-optimal for water flows, a computational fluid dynamics (CFD) analysis was completed to identify a ‘best practice’ design to reduce dead spots and protect water quality. As the new tank footprint was partially on virgin ground and partially on ground where the previous structure had stood, there was a risk of differential settlement. To mitigate this risk, a tailored ground investigation was conducted to obtain data for a predictive settlement analysis to inform the engineered fill design and ensure a robust outcome. [caption id="" align="alignnone" width="1200"] Tank under construction, showing precast concrete slabs being maneuvered into place by a crane - Courtesy of Stonbury[/caption] Design Mason Clark Associates was responsible for the civil and structural design of: The reinforced concrete twin-compartment reservoir, excluding the detailed design of precast roof slab panels. The reinforced concrete valve house. The surface, underdrainage, and foul water drainage systems. The external steel roof access staircase. The client stipulated that each cell would require the following features: Opposed high-level inlet and a low-level outlet, connected to the existing network. Automated control valves. Combined metered washout/overflow pipe. Overflows with sufficient capacity to take design inflow whilst maintaining sufficient freeboard to the soffit of the roof. Washouts, sized suitably to enable the drain down of each cell over a 24 to 48 hour period without causing flooding to surrounding watercourses. Sufficient ventilation to ensure that each cell is not over-pressurised during filling or a vacuum created during drawdown. Access doors and hatches to meet LCPB 4 rating and SEMD requirements. All necessary ductwork for telemetry and security cabling. Mains alterations to accommodate the new reservoir. Arrangements for taking compliance samples. The proposed tank was to have an approximate footprint of 850m2 and operate with a top water level of 79.2mAOD (ground level is approximately 71.4mAOD). The inlet was to be connected to the pumping main, whilst the outlet connected to the same main as Bourn Reservoir 3 so that they would operate hydraulically together. The placement of inlet and outlet valves, baffle walls and weir boxes were designed in accordance with results from the CFD analysis. [caption id="" align="alignnone" width="1200"] Demolition of the disused circular tank prior to construction - Courtesy of Stonbury[/caption] Addressing the drive to build assets with lower embodied carbon and to reduce the length of the programme, the design incorporated the use of precast concrete roof slabs in addition to conventional in-situ pour concrete. This was preferred to a fully precast solution due to the risk of perennial ingress issues at precast joints. This would help to reduce embodied carbon by approximately 10% compared with a traditional build and make the 48-week programme possible. The structural elements of the reservoir and pipework were to have a minimum design life of 50+ years, and 20+ years for all other elements. All structural and geotechnical design was in accordance with the relevant section of the Eurocodes, and all concrete elements were designed with a water-tightness classification of 1. All work was designed to be carried out in accordance with the latest CESWI, WIMES and Cambridge Water Company general engineering specifications and to meet DWI requirements for potable water storage units and the current SEMD guidance. Environmental management A Project Site Environmental Assessment sought to register and mitigate site-specific environmental impacts such as noise, land and watercourse pollution, waste materials and damage to local ecology. Identified environmental risks were controlled through measures detailed in Risk Assessments and Method Statements. A preliminary ecological appraisal was undertaken during the pre-construction phase to determine the presence of dedicated nature conservation sites and protected species in proximity to the site. The site was not within or near an SSSI. No notable plant species were identified but some notable animal species were. Recommendations were provided based on the ecological mitigation hierarchy to avoid, mitigate, and compensate during and after the programme. [caption id="" align="alignnone" width="1200"] Construction workers building reinforcement cage for walls - Courtesy of Stonbury[/caption] Health & Safety A detailed H&S file was prepared for the client. During construction, special site-specific health and safety considerations were planned, managed and monitored using a variety of means, including: Site-suitable PPE. Approved RAMS. Vibration, noise and CoSHH assessments. Daily Point of Work Risk Assessments (PoWRAs). Suitable barriers and safety signage. Obstructions or trip hazards protocol. Agreed working hours and strict adherence to quiet periods. Asbestos protocol. Demolition In 2020, existing services into Reservoir 2 were disconnected and removed in preparation for tank demolition. Due to the spatial constraints of the site, demolition was carefully planned with an appropriate methodology to mitigate risk to the live operational tank. An excavator was employed to demolish the roof, with an attached claw to cut the concrete walls into small vertical sections. All broken material was pushed into the middle of the tank during demolition to protect the adjacent asset. Once demolished, material was removed from site. [caption id="" align="alignnone" width="1200"] The site for the new reservoir after demolition of the previous tank - Courtesy of Stonbury[/caption] Site preparation A site compound was constructed for offices and welfare facilities. This area also had space for limited parking, temporary materials storage and a turning area for construction vehicles. Heras fencing was erected on the boundary of the compound area and construction warning notices were posted at the site entrance gates. To prepare the area for the reservoir, the locations of services were pre-determined using a combination of existing service drawings, site knowledge and CAT scanning using a signal generator followed by hand-excavated trial holes. Base construction The site for the new tank was excavated, removing spoil and saving a small stockpile for backfilling. Old balancing pipework was removed, and the existing pipes were capped so that they could be reconnected upon project completion. Underdrains were installed. Fill-to-base was completed in accordance with the design informed by the predictive settlement analysis. The area was levelled, filled with type 1 material to the specified formation level and rolled. A 50mm concrete blinding base was poured from a dumper and levelled by hand. Concrete square bars were laid by hand to support the reinforcement steel placed directly on the blinding slab and tied, ensuring correct laps in accordance with the design. Timber formwork was levelled using a laser level placed on each end. Once this was braced, the floor was completed in four separate concrete pours. The sump was poured at the same time using a concrete pump and vibrated constantly as the concrete entered the reinforcement. [caption id="" align="alignnone" width="1200"] Formwork panels - (left) outside view during construction of the upper wall, and (right) inside view during construction of walls and columns – Courtesy of Stonbury[/caption] Wall construction A panel system with film-faced plywood was built for the wall and column formwork according to drawings. Completed shutters were lifted into place using an excavator for the 3m high lower walls and a tower crane for the 7.8m high upper walls. Reinforcement cages were fabricated on the ground and lifted into position with a tower crane to minimise working at height. Inner shutters were held in place with push-pull props drilled and fixed to the base slab. Outer shutters were fixed using Dywidag bolts and tie bars on the outer edge. Timber stop ends were fixed to the ends of the shutters. The concrete was poured in sections and vibrated as filling proceeded, employing both external formwork vibrators and 10m long internal vibrators to achieve the required concrete finish. Shutters were lifted, cleaned and re-positioned for each 5m wide pour section. Once all sections were full, laser levels were used to check levels and tops were floated off. Pipework At this stage, trenches were excavated for overflow and outlet pipework. Outlet pipework was installed first and connected to the existing valves. A flow meter was installed in line and a chamber was built around it. Pipes were capped prior to installation, chlorinated and bagged off to prevent contamination. Once installed, pipes were pressure-tested and the trenches were filled with stone and backfilled in layers. The flow meter chamber was excavated using a 5-tonne excavator and concreted with formwork and vibration. A Technocover lid was drilled and fixed to the cover slab and a galvanised ladder was affixed to gain access to the flow meter. Ducting was installed for the control panels and mains power. Once the main walls were complete, internal access and pipework were installed. [caption id="" align="alignnone" width="1200"] Construction workers guiding precast concrete roof slabs into place - Courtesy of Stonbury[/caption] Roof construction To construct the roof, 30 steel beams were lifted onto the reinforcement cage using a tower crane with two operatives in scissor lifts to guide them. The tower crane was then used to manoeuver 86 precast concrete panels (150mm) to create the roof slab. The panels were attached to the crane with a four-legged chain and lifted into position, guided by operatives in scissor lifts. Once all the panels had been placed on the roof, the joints were in-filled with concrete ready to take a 150mm structural concrete screed and Lytag levelling screed, laid with a fall of 1:80 front to back to allow water to run off from the roof. The outer walls were washed, spray-primed and painted with anti-carbonation green camouflage paint to protect the concrete from weathering and reduce visual impact from the road. A waterproof liquid seamless coating system was applied to the tank roof with anti-slip walkways. Finally, a permanent exterior access staircase and perimeter handrailing were installed. Leak tests The reservoir was filled with water and underwent a seven-day drop test to ensure there were no leaks. Once successfully passed, the tank was drained for a final inspection, clean and chlorination. Outside, attenuation drainage was installed and security fencing was erected. MEICA elements were installed by specialist contractor IWS Mechanical & Electrical. Their scope included a full ICA upgrade of the site, reservoir level monitoring, electronic security and electrical distribution for the site. [caption id="" align="alignnone" width="1200"] (left) Construction worker using the newly installed exterior staircase, and (right) the completed tank undergoing an integrity inspection - Courtesy of Stonbury[/caption] Post-construction Earlier CFD modelling and ground investigations had indicated the requirement to fill both cells immediately upon commissioning and keep them simultaneously in use for the first six months of operation to ensure ground was consolidated following the build. As a consequence, the inspection of the internal dividing wall could not be completed during the asset handover. To provide assurance to the client, Stonbury arranged to undertake a further inspection after six months, which confirmed integrity. Conclusion The project was completed according to programme without delays or health and safety incidents. The new tank was connected to the network in October 2022 and will increase water security within Cambridgeshire for decades to come.

Guildford town and the surrounding residential areas are currently served by an existing sewage treatment works (STW) located adjacent to the River Wey, just north of the town centre. The land which this occupies has been identified as part of the Slyfield Area Regeneration Project (SARP), which includes the new Weyside Urban Village (WUV). This mixed-use regeneration project will include circa 1,500 new homes, new community facilities and 6,500m2 of commercial space to improve the local area. Thames Water Utilities Ltd (TWUL) is working in partnership with Guildford Borough Council (GBC) to move the STW to a new location, which is not suitable for housing.

The location chosen is on the north-east extent of the existing Slyfield Industrial Estate and is on an area previously used as a landfill site. In August 2023 Water Projects published a case study which provided insight into the extensive pre-construction design for civil and process engineering elements of the project. This article delves into the construction of the project and provides an update on the significant progress made to date on site.

Site historical use

The site for the new STW is approximately 70,000m2 and was previously used as a landfill site. It had originally been used as sand and gravel quarries and then subsequently used as landfill from the 1960s to the 1980s.

The landfill material is generally domestic and light industrial. It consists of black bag waste, timber, plastics, fabrics but contains fragments of asbestos and other materials.

The site was capped off with a granular layer in the early 1980s and has laid dormant ever since. The landfill depth varies across the site from between 2m and 6m thick. This then overlies an alluvium layer, sands and gravels and London Clay. The depth of the London Clay is approximately 10m below existing ground level.

[caption id="attachment_16131" align="alignnone" width="1200"] A screenshot of the 3D model used for design and construction - Courtesy of Bam Nuttall Ltd[/caption] Civil engineering: Basis of the design

Typically, major structures within a sewage treatment works are built below or partially below ground level to maximise gravitational energy. The new Guildford STW differs in that the strategy is to deliberately design and build above ground as far as practicable.

This is to minimise the disturbance to, and removal of the existing landfill thereby reducing the impact on the environment and the cost of disposal.

Undertakings

After a period of Early Contractor Involvement, Thames Water awarded a contract to BAM-Enpure Joint Venture (BEJV) in 2021 to design, build and commission this significant new works and once operational, to de-commission the existing works.

BEJV is a non-integrated joint venture, formed specifically to combine the excellence of experienced civil engineering contractor Bam Nuttall Ltd and the process engineering/MEICA specialism of Enpure Ltd to deliver a turnkey solution for Thames Water. The workscope split is as follows:

Bam Nuttall Ltd: Civil engineering workscope Principal contractor Civil engineering design Ground stabilisation & piling Structures Underground pipework Tunnels, shafts and connections Buildings Outfall pipeline & structure Roads, fencing & general civil engineering works [caption id="attachment_16143" align="alignnone" width="1200"] Construction of the high level inlet works structure - Courtesy of Bam Nuttall Ltd[/caption] Enpure Ltd: Process engineering/MEICA workscope Principal designer MEICA design Process design Mechanical works Electrical works Control systems Commissioning

Decommissioning of the existing STW will also be undertaken by BEJV, in addition to working collaboratively with TWUL operational and networks teams to integrate existing TWUL operational assets into the new sewage treatment works.

Site trials

BEJV undertook a series of site trials in 2021/2022. The purpose of this was to investigate the proposed ground improvement techniques further in order to validate proposals and inform detailed design. There are a combination of techniques which interface with each other in a complex manner.

The trials also gave important information about potential effects to both leachate levels and ground gas within the existing landfill to ensure there would be no impact on environment, ecology and human health.

Four trial areas were chosen, to provide a variety of conditions and in each of these areas a set of boreholes was established at increasing offsets away from the trial areas. These boreholes contained monitors for both leachate levels and ground gas volumes and were monitored 24/7. In addition, noise and vibration monitoring was also undertaken. [caption id="attachment_16140" align="alignnone" width="1200"] (left) Rapid impact compaction underway and (right) a selection of site plant in use - Courtesy of Bam Nuttall Ltd[/caption]

The three techniques tested, and subsequently used within the works were as follows.

1. Rapid impact compaction (RIC): RIC was undertaken to remove the risk of long-term settlement to the landfill. Whilst the main structures would be supported on piles, this was to remove the risk of long term ground settlement underneath and around the structures. RIC is a method of imparting energy to the ground using a repeated but relatively short drop-weight, where a base plate is in constant contact with the ground. It is undertaken on a pre-determined grid pattern. At Guildford a 9T hammer was chosen, fitted to a 35T base machine and working on a 2.5m x 2.5m grid. Each ‘pass’ of the technique used 40 blows at each point.

Within the trial areas the technique was tested with 1, 2 or 3 passes (ie, 40, 80 or 120 blows per location). Cone penetrometer tests were used to measure the extent of deep level ground compaction before and after the trials. The continuous monitoring from the boreholes demonstrated that at each ‘thump’ of the ground there was no discernible change in leachate levels or ground gas volumes, and that there was no dispersal of leachate happening throughout the landfill.

From the trials it was determined that all areas of the site that are being built on should receive either 1 or 2 passes of RIC for the permanent works.

[caption id="attachment_16135" align="alignnone" width="1200"] (left) Driving precast concrete piles and (right) vertical rigid inclusion installation - Courtesy of Bam Nuttall Ltd[/caption] 2. Precast driven piling: The main structures and pipelines are founded on precast driven piles. These are end-bearing into the London Clay, approximately 10m below ground level. Precast driven piles were chosen as the solution as the operation does not bring any landfill to the surface. Various size piles were driven to various depths and tested with both dynamic and static tests. Borehole monitoring showed that there was no discernible change to leachate and ground gas levels and that there was no dispersal of leachate happening throughout the landfill.

3. Vertical rigid inclusions (VRI): VRIs are mass concrete piles which are used for lightly-loaded structures and areas such as roads and hardstandings. They are a displacement pile, with the surrounding soil pushed sideways by an auger. As the auger is withdrawn the resulting void is filled with concrete up to ground level. They therefore work by increasing the density of the ground. A granular layer is then installed above to remove any ‘hard spots’. Again, this technique does not bring landfill material to the surface. It was trialled in two areas and found to be suitable for use, without causing any effects to leachate levels or ground gases. It is therefore being used as part of the permanent works over the whole site wherever there are not piled structures.

The trials of all three techniques, together with the subsequent site testing proved that the design principles were correct, and gave information on how to refine the solutions further. It also demonstrated that the techniques would not cause any adverse environmental effects.

[caption id="attachment_16142" align="alignnone" width="1200"] (foreground) Ferric mixing and flocculation chambers and (background) concrete bases for sludge tanks - Courtesy of Bam Nuttall Ltd[/caption] Guildford STW: Civils works supply chain - key participants Main contractor: Bam Nuttall Ltd Planning consultant: Adams Hendry Consulting Ltd Civil engineering design: Arcadis Group Ltd Boreholes & testing: Geo-Environmental Services Ltd Asbestos monitoring: Socotec Ltd Rapid impact compaction: Cofra Ltd (Boskalis Group) Vertical rigid inclusions: Foundation Piling Ltd Concrete piling: Aarsleff Ground Engineering Ltd Temporary works specialist: Mabey Hire Ltd Temporary works specialist: MGF Ltd Tunnels & shafts: Joseph Gallagher Ltd In situ concrete works: Kelly Formwork Ltd Precast concrete works: DJ Civils Ltd Precast concrete manufacturer: FLI Precast Solutions Precast concrete manufacturer: A-Consult Ltd Soil processing: Remediation Waste Management Services Concrete supplier: Heidelberg Materials Gas protection: PAGeo Contracting Ltd Crane supply: Delden Cranes Enabling works

Enabling works took place during Spring 2023 and consisted of site clearance, setting up the site offices and welfare and establishing fencing. The whole site was then covered with a 100mm thick layer of imported granular material to provide further protection against the risk of asbestos within the existing capping layer.

A series of 20 further boreholes were installed around the perimeter of the site to enable daily monitoring of both leachate and ground gas within the landfill and to ensure that none was being mobilised by our works. Mobile monitoring stations for noise, dust, vibration and asbestos were all set up, which are monitored continuously throughout the works. Over half a million data points have already been captured.

[caption id="attachment_16138" align="alignnone" width="1200"] Piles and blinding concrete for the four final settlement tanks and (left) temporary ground support for pipelaying into the centre of the tanks - Courtesy of Bam Nuttall Ltd[/caption] Guildford STW: MEICA works supply chain - key participants Main designer/contractor: Enpure Ltd CFD analysis: The Fluid Group Cake silo: Saxlund International PST scrapers & ferric dosing plant: Colloide Inlet works & PST odour covers: Power Plastics Ltd Grit remover plant: Jacopa Escalator screens: Longwood Engineering Imported sludge Strainpress: Huber Technology Sludge thickening & dewatering: Kent Stainless Ltd Odour control plant: Odour Services International Ltd FBDA grids & blowers: Xylem Water Solutions Cloth pile filters: Eliquo Hydrok Ltd Storm tank cleaning system: Sulzer Pumps Wastewater Ltd Tank logging system (WASP): JR Pridham Services Ltd Glass lined steel tanks: Balmoral Tanks Ltd Sludge tank mixing: Landia UK Ltd Transformers: Wilson Power Solutions Ltd Groundworks and foundations

The permanent works started in earnest in Summer 2023 and in August, rapid impact compaction was conducted over the site, with a combination of one or two passes, as informed by the results of the previous site trials. In total the ground was hit 360,000 times! Precast piles were then driven for the major structures and pipelines. These were all 250mm square piles and varied in length from 16m to 20m. A total number of 3,422 piles have been driven using three piling rigs.

Vertical rigid inclusion installation is currently underway, with a total of 1,700 out of 9,000 already completed. The works are sequenced to avoid clashes with other work areas, on what is a congested site. Following installation, each work area is left for the piles to cure for the following seven days, thus effectively sterilising large areas of the site at a time. This therefore requires detailed collaborative planning on all work fronts to ensure that the site can remain operational.

[caption id="attachment_16136" align="alignnone" width="1200"] Activated sludge plant precast walls erected, prior to pouring base slab and concrete stitches - Courtesy of Bam Nuttall Ltd[/caption] Concrete structures

Of the 59 concrete structures, some are simple reinforced bases, however ‘the big 5’ are significant structures:

Inlet works. Primary settlement tanks (PSTs). Activated sludge plant (ASPs). Final settlement tanks (FSTs). Tertiary treatment plant (TTP).

Due to the repetitive nature of their construction, BEJV chose to construct the PST and the ASP using precast concrete techniques, which are then stitched together on site. The four FSTs and two storm tanks are also being constructed using precast panels which are then post-tensioned.

The inlet works and TTP are complex, bespoke structures with very little repetition and so are more suited to traditional in situ concrete construction. The inlet works is a particularly complex structure, and is the tallest structure on site at 13m above ground level and being formed of five separate elements.

As of August 2024, the inlet works concrete structure is half complete and the TTP structure underway. The PST precast walls are mostly in place and stitched together, with roof beams now being installed. Works have also started on the ASP walls.

Pipework to the FSTs is underway, which will then allow the construction of the bases to follow on. To date (August 2024), 4,000m3 out 14,000m3 of concrete has been poured, and 205 out of 454 precast wall elements installed.

[caption id="attachment_16141" align="alignnone" width="1200"] (foreground) PST precast walls with concrete stitches and bases and (background) ASP precast walls - Courtesy of Bam Nuttall Ltd[/caption] Transfer tunnel

The flows to the existing STW enter at the southern end of the works. A new transfer tunnel has therefore been constructed to intercept this and transport the flows to the new STW. This tunnel is 1.4km long, 1.5m internal diameter and flows by gravity. It is formed at an invert depth of 10.6m to 15.7m below existing ground level, entirely within the London Clay.

To construct the tunnel a series of six shafts were sunk. The largest of these is 12.5m diameter and forms the inlet shaft in the new STW. The raw sewage will then be pumped from this to the inlet works, from where it will then flow by gravity through the new STW. The remaining five shafts were used to launch or receive the tunnel boring machine (TBM) and pipe-jack, as well as being used for auxiliary connections to sewers in the existing network which don’t get picked up by the main connection.

The tunnel was constructed using the pipe-jacked method using a tunnel boring machine. This was named ‘Daphne’ in a competition by Bisley Church of England School. Daphne Jackson was the first female physics professor in the UK and taught and researched in Guildford. The tunnel consists of four straight sections, one curved section and one short hand-dug section to connect to the existing network.

Current progress is that all of the shafts have been sunk, the main tunnel is complete and fit out the shafts has commenced.

[caption id="attachment_16139" align="alignnone" width="1200"] Safdar Ali, Andrew Dawes and Izhar Ahmad from the BAM team at the completion of the tunnel - Courtesy of Bam Nuttall Ltd[/caption] Outlet

The outlet for the new STW consists of a 750mm diameter pipe from the TTP and a 1050mm diameter pipe which acts as a storm overflow during extreme weather events. These pipes are laid across a floodplain to the River Wey, a distance of approximately 330m before discharging via a bespoke headwall into the River Wey. This has been designed in conjunction with Environment Agency to minimise erosion in what is classified as a salmon river.

Due to Environment Agency and Local Authority permitting requirements as well as practical requirements of working on a floodplain with underlying running sand, these works are practically restricted to a short duration in the summer. This is being undertaken during Summer 2024 and the works are on target for completion within this period.

Below-ground pipework

The majority of underground assets in the new works are being constructed within the existing landfill. This brings plenty of challenges in both design and construction. Assets must be designed to withstand both differential settlement and potential degradation from existing contaminants in the land fill material.

A variety of ductile iron, carbon steel, and concrete pipes are being used with various protection methods. The work is being self- delivered by the BAM workforce and the installation of below-ground pipework is underway with a focus on where it interfaces with the new structures. This requires extensive temporary works solutions to provide a safe working environment for the workforce within the band of landfill material.

Steel sheet piles are being used to provide temporary ground support and excavated landfill material is being sorted in a material handling area on site. This is being done to reduce the amount of hazardous material being sent off site, halving the amount of excavation and disposal required using traditional open cut methods.

[caption id="attachment_16133" align="alignnone" width="1200"] Threading buried process pipework between new structures requires extensive temporary works - Courtesy of Bam Nuttall Ltd[/caption] Integration of existing assets

As well as the main connection taking flows form the existing works to the new, there are three other existing assets which are to be integrated into the new system, at various points along the length of the new tunnel. This involves extensive research and planning in an open and collaborative approach with TWUL networks teams.

Bowers Farm Main was successfully diverted in November 2023, and has been constructed such that the final connection and commissioning to the new system will be a more straightforward operation. Planning works are currently underway on both Stokes Road syphons and Abbotswood syphons in order to construct similar scenarios for future connection and commissioning.

The main connection to the existing Guildford Main at the head of the new scheme entails connecting into an existing 10m deep concrete and brick built chamber, which carries live flows 24/7. The site team have undertaken several successful drawdowns in conjunction with TWUL to ascertain the dimensions and condition of the chamber in order to plan the final breakthrough works in great detail. This design work is currently underway and the new tunnel hand drive has been stopped a few metres short of the final breakthrough and shored up, prior to the final connection to the existing network.

[caption id="attachment_16164" align="alignnone" width="1200"] (left) Concrete bases for the tertiary treatment plant, (top right) cross-sectional view through the primary settlement tank, showing the piles and gas dispersal layer beneath the base, and (bottom right) precast wall panels are joined with an in situ concrete stitch - Courtesy of Bam Nuttall Ltd[/caption] Future works

Construction works of the ‘Big Build’ are continuing at pace and the BEJV Team are now focusing on ensuring a safe, effective and efficient integration of civils and MEICA elements. This will start in late 2024 and continue throughout 2025.

Following successful completion of commissioning of the new sewage treatment works in 2026, the existing works will be de-commissioned making way for the next stage of the Weyside Urban Village, providing homes and leaving a true legacy for local people and businesses.

As assets age, they start to work less efficiently than they did at their installation. Anglian Water proactively CCTV surveyed the sewers and found evidence of hydrogen sulphide attack, which corrodes concrete sewers resulting in weakening of the pipework and eventual collapse. In September 2023, the @one Alliance Sewer Rehabilitation Team completed a project in Grays, Essex, off the A1012 Treacle Mind Roundabout near the A13, where they rehabilitated over 840 meters of 900mm concrete sewer pipe along Lodge Lane - a crucial lifeline for a highly populated residential area. Planning

From the outset, it was clear that this undertaking would require an innovative approach beyond conventional sewer lining and over pumping techniques. Two main challenges were faced by the project team.

The first challenge was to determine how to rehabilitate a 324m manhole-to-manhole stretch at this massive diameter at such a busy location and under tight highways restrictions. The team realised that they needed to trace the line and identify an optimal location for a new access point - a crucial step to break down the sewer into more manageable sections. Considering that the sewer crosses Lodge Lane halfway through, added with the need to avoid existing services and our bypass pipework, it became apparent that this was not a viable option.

[caption id="attachment_13360" align="alignnone" width="1200"] Overpumping pipework - Courtesy of @one Alliance[/caption]

The second challenge the team faced was the need for the sewer to be empty while the rehabilitation works took place. The team decided that in order to resolve this challenge, they needed to install a temporary above-ground pipe to divert the sewage flows.

This job was a significant undertaking, and one that required close collaboration with Vanderkamp UK. Working together, the @one Alliance/Vanderkamp UK team considered sustainable solutions to mitigate flows and ensure the continued integrity of Anglian Water’s infrastructure.

To manage flows and ensure uninterrupted service to customers, temporary connections were established on the existing 600mm and 375mm dia. rising mains within the Treacle Mine Roundabout. These mains, originating from the Stifford Corran Way and Stifford Clays Pumping Stations, require pumping of up to 350 l/s.

The aim was to maintain seamless flow and mitigate any potential flood risks, so the bypass was routed through in-line duty/standby booster pumps strategically positioned within the roundabout. This innovative approach eliminated the need for suction pits or wet wells. Through extensive modelling, the team identified the need to incorporate booster pumps, as the existing pumping stations could not pump the additional 1km of 500mm bypass pipework, which included 16 pipe bridges and hoppers.

Vanderkamp UK undertook continuous and meticulous remote monitoring which ensured the successful execution of this complex and critical project.

[caption id="attachment_13366" align="alignnone" width="1200"] Vanderkamp UK’s temporary overpuming pipework while OnSite Cental undertake the CIPP lining works - Courtesy of @one Alliance[/caption] Grays Sewer Rehabilitation: Supply chain - key participants Client: Anglian Water Project delivery: @one Alliance Bypass pipework (1km of 500mm pipe): Vanderkamp UK Cured in place relining: OnSite Central Ltd CIPP liner supply: IMPREG GmBH Traffic management: TBF Traffic The 324m manhole to manhole stretch

Addressing the first challenge of rehabilitating the large manhole to manhole stretch, the team collaborated closely with Tier 2 Supply Chain partner OnSite Central Ltd, to prove a cured in place pipe (CIPP) relining solution. The @one Alliance challenged OnSite to develop a game-changing method that would enable a one-shot installation of the 324m length.

After exploring various options, including a single-cure installation that posed complications due to power cables, a 50/50 cure approach was selected, partially curing the liner in both directions.

To ensure the liner’s integrity throughout this process, OnSite Central Ltd ingeniously employed special sluice bags to keep the liner inflated while moving the light train to the other manhole; effectively preventing any shear damage to the liner during the transition between cured and uncured sections.

[caption id="attachment_13362" align="alignnone" width="1200"] OnSite Central’s CIPP lining operation - Courtesy of @one Alliance[/caption]

The deployment of specialised equipment, including a large 20-ton winch, a larger roller bed, crane pads, and sluice bags, incurred additional costs, however, savings totalling approximately £35k included avoiding the need for an additional liner installation, a week of over-pumping, and substantial running costs. Additional significant savings were gained by removing the requirement for a new 6m deep access point and extended road closures.

In terms of sheer length, this installation now holds the record as the longest the Anglian Water @one Alliance Sewer Rehabilitation Team has ever undertaken. OnSite also suspect that it might even be a record-breaker for UV installations in the UK, if not globally! Typically, cable length restrictions cap such installations at around 300 meters, making this 324m achievement truly exceptional!

Challenges

As with any project, challenges arise. Added to the previous challenges mentioned, the team had plenty more to overcome.

Ensuring resources: Learning from concurrent @one Alliance projects, from the outset, the team knew that they needed to ensure resources were available for the project to commence, therefore early resourcing was required to overcome issues on programme later down the line.

Avoiding planning issues: Once the project started, the tight highways restrictions throughout and multiple live permits in the area could have caused planning issues if the team had not realised these early and planned for them at the start of the project, so they worked with Highways early to identify a suitable working window.

[caption id="attachment_13363" align="alignnone" width="1200"] Traffic management during the works - Courtesy of @one Alliance[/caption]

Emergency road closure: Another issue was having to emergency-close Lodge Lane due to two leaks across the pipe bridges. The team identified these by using treated final effluent to ensure no pollution events would occur. To resolve this issue, an emergency road closure was put in place on Lodge Lane for 2 hours from 8-10 PM in order to safely access the pipework at the leaks and tighten the bolts. After collaborations with Highways the closure in place safely put in place.

Additional cleaning: Once flows had been diverted and a detailed CCTV survey was undertaken, it was apparent that more cleaning of the sewer pipe was required, taking longer than was originally anticipated. In order to claw this time back and ensure the project completed on time, the team installed two liners in a week. To do so, the final liner installation needed to be extended into the weekend. This required an adjustment to the road closures on Windsor Avenue which was agreed with Highways and communicated to the local residents.

Avoiding potential issues: Challenges do not only affect the project team; they also affect customers. The team was made aware of visibility issues due to the temporary pipework obstructing the view from a junction, creating a potential blind spot. Responding promptly to feedback from the public, the team worked with the Highways Inspector to install temporary mirrors and mitigate the issue.

Customer engagement

The @one Alliance has a clear purpose to bring environmental and social prosperity to the Anglian Water region, and this is dones by ‘Making Today Great – every day, in every interaction’.

[caption id="attachment_13365" align="alignnone" width="1200"] Customer information boards - Courtesy of @one Alliance[/caption]

The @one Alliance was aware that the work at Grays would impact customers throughout the project lifecycle, so processes were put in place to effectively communicate with customers across the area in a variety of ways.

Open day: On April 26th, 2023 an open day was hosted at Stifford Parish Hall to give the community the opportunity to meet the team and ask any questions or share any insights before the project began to ensure they had a clear idea of the plan for the project. Communications: Customers were notified about the works via letters, emails, SMS campaigns and a dedicated scheme board. In total, over 1,444 letters and 970 emails were sent to residents on top of 13 SMS campaigns which resulted in 2,755 customers receiving text messages to let them know of specific road closures and project updates. Social media: Projects updates were regularly updated on Anglian Water’s “In Your Area” website for customers to view and on its Facebook page. The Facebook page reached 63,387 customers in total throughout the project. CSAT score: A record number of 9+ scores were received for a scheme with a resulting in a 9.18 CSAT score.

Meticulous planning ensured customers were aware, questions were answered, and feedback was received. Overall, customers have praised the work that has been undertaken; emphasising the minimal disruptions and their appreciation for the use of temporary traffic lights.

Outcome

The works started in June 2023 and completed in September 2023 with the removal of the temporary pipe bridges and traffic lights. Over 840 meters of 900mm sewer pipe have been successfully rehabilitated along Lodge Lane. The project was delivered on time, and gained positive customer feedback, positive relationships with the local council and Highways authorities and a great working relationships with our Tier 2 suppliers Vanderkamp UK and Onsite.

When you’re installing sheet piles at the end of a residential cul-de-sac, next to an adjacent river, your installation method needs to be silent, vibration-free and environmentally friendly. Add hard ground conditions into the mix and you’re going to need our Giken Supercrush solution. Lady’s Walk is a picturesque footpath on the bank of the River Wansbeck in Northumberland, connecting Morpeth town centre with the nearby village of Mitford. During the rainy Easter weekend 2018, 35m of river retaining wall and footpath subsided and fell into the river.Northumberland County Council engaged the services of Ivor King to install a sheet piled retaining wall in to order to stabilise the land, enabling necessary repairs to be carried out and ultimately for the public footpath to be reinstated. Challenges & Solutions Hard ground conditions, environmental issues and extremely restricted access made this project particularly complex; site access was via a 3.2m wide residential cul-de-sac, with neighbouring properties within close proximity and an environmentally sensitive riverside location. Using Giken Supercrush technology, we were able to overcome hard ground conditions, whilst pressing-in piles using silent vibration-free methodology. This ensured minimal impact to residents in neighbouring properties as well as protecting local flora and fauna in and around the adjacent river. (Note: in the video below, pay special attention to the group of ducklings swimming past undisturbed, oblivious to the installation, proving our Giken solution really is silent and vibration-free!)

Riverbank sheet piling to enable reinstatement of public footpath - Courtesy of Ivor King - The Piling People

Furthermore, the expertise of our in-house transport team was called upon, with all deliveries were meticulously planned and executed by Ivor King Transport into a site where access was extremely tight and barely wide enough to accommodate an articulated lorry. Once our sheet pile retaining wall installation was complete, repairs could take place to the the riverside path with eventual reinstatement and reopening of this popular walking route in Northumbria. Location: Lady's Walk, Morpeth Client: Northumbrian County Council Project cost: c. £269k Completion date: November 2018 Project period: 8 weeks Plant utilised: Giken Supercrush Silent Piler JCB JS360 Excavator with Side Grip Movax Attachment Marchetti Crawler Crane

The BNM Alliance (a joint venture between Barhale and North Midland Construction) awarded Aarsleff the contract to design, supply and install a soil nailed slope to allow, with associated works, the launching of a tunnel boring machine for the Severn Trent Elan Valley Aqueduct Rehabilitation project in Wales. The original aqueduct was built between 1893 and 1904. Fast forward over 100 years and the aqueduct still provides drinking water from the Elan Valley to Severn Trent’s customers in Birmingham. The aqueduct transports high quality water entirely by gravity. Having supplied water for over 100 years, the aqueduct is beginning to tire in three key locations and offline replacements are necessary. 8 (No.) test nails were installed on the 17th July. These were tested to destruction to confirm the design prior to production works starting. With its Klemm 806 rig, Aarsleff will then installed 670 (No.) 100mm diameter fully galvanised R32 -280 self-drilling soil nails of 6-16m in length. [caption id="" align="alignnone" width="1200"] Courtesy of Aarsleff Ground Engineering Ltd[/caption] In addition to the soil nails, approximately 670 (No.) head plate and nut were supplied and fixed. The soil nailed wall has an estimated 1250m2 area to which Aarsleff has supplied and fixed a steel mesh and geotextile facing. Aarsleff were on site from 24th July with completion 15th September 2017. Aarsleff showcased its previous work in soil nail projects of similar size to the main contractor before winning the contract to demonstrate its technical capabilities and expertise whilst simultaneously, assuring the client of cost, time and quality. Aarsleff has sought value engineering primarily through optimisation of the soil nail layout and facing mesh. The self-drilling soil nails were procured from Barnsley-based Minova and possess a hollow bar, which is used for drilling ether with water flush, air flush or cement grout flush and are extended by using couplers. The standard couplers have a design which ensures end-to-end bearing of the hollow bars to transfer percussive energy from the top hammer to the drill bit whilst a sealing ring in the centre stop, minimised flush spillage during drilling. The soil nails also possesses a sacrificial drill bit. [caption id="" align="alignnone" width="1200"] Courtesy of Aarsleff Ground Engineering Ltd[/caption] The rig we employed is designed for the use of powerful double head drilling units, hydrualic drifters or rotary heads. It can also be equipped with drill masts either with feed gear or cylinder feed systems, with the option of fitting lattice mast extensions, the modularity of which, allows the adaption of a variety of options, which makes the drill rig ideal for anchoring, micro piling, jet grouting and even geothermal drilling. After completion, two percent of all working nails will be ‘Acceptance’ tested to validate the design and provide confidence as to the quality of the installation. [caption id="" align="alignnone" width="1200"] Courtesy of Aarsleff Ground Engineering Ltd[/caption] Scope of works 670 (No.) 100mm soil nails 670 (No.) head plate and nut 1250m2 steel mesh and geotextile facing   For more information: Aarsleff Ground Engineering: +44 (0)1636 611140 | www.aarsleff.co.uk

   

J Murphy Group awarded Aarsleff the contract to install a temporary sheet piled cofferdam on the River Severn, as part of the £300 million Birmingham Resilience Project. The scheme is one of Severn Trent’s largest ever infrastructure projects, specifically to develop an alternative water supply for Birmingham to complement the Elan Valley Aqueduct (EVA). The Birmingham Resilience Project will create a new abstraction point and pumping station on the River Severn, at Lickhill Quarry near Stourport, to which water will then be pumped along a new 25km pipeline, through pipes with a 1.0m diameter, to the water treatment works in Birmingham. Aarsleff’s sheet piling works allowed a dry working area for J Murphy to construct the secant piling to the intake structure. Sheet piles will then be subsequently removed and the entire structure submerged. Water is to be taken from the River Severn which will provide a new source for the aqueduct, while maintenance takes place on the original EVA. When the resilience plan is in operation, the city of Birmingham will be drawing water from at least four sources, rather than just one. Early contractor engagement between J Murphy and Aarsleff identified significant technical deficiencies in the early engineering proposals for the temporary works cofferdam. Aarsleff’s proposed design was safer, quicker and cheaper with significantly less risk to the environment, their clients program and operatives. Aarsleff installed the bespoke temporary sheet piled cofferdam which comprised 154 (No.) AZ26-700 steel sheet piles, with an integral enhanced toe support system comprising of 53 (No.) H-Section piles. These were required due to the very shallow underlying bedrock, which only allowed for a limited sheet pile penetration. Access was provided by a temporary access works platform allowing safe working over water. Aarsleff employed a high frequency vibratory hammer and an impact hammer to drive its piles (using panel driving techniques) and employed a 110-tonne capacity mobile crane operating at a maximum 25m radius to unload and handle piles and hammers. [caption id="" align="alignnone" width="1200"] Courtesy of Aarsleff Ground Engineering Ltd[/caption] Senior technical estimator Ashley Carter said:

“This was a technically challenging scheme to be involved with requiring a lateral thinking approach to resolving the challenging problems. The prestigious project demonstrates the high level of experience and expertise Aarsleff’s sheet piling department can offer to its clients”.

Aside from delivering the project on time and within budget, Aarsleff were also able to reduce risk and environmental damage. Risk reduction through application of practical construction methodology, and Reduction in Environmental impact, (as the original scheme involved drilling underwater and spoil flushed directly into the watercourse). Steel sheet piles will also be recovered for re-use making this element of the scheme carbon neutral. Aarsleff took the technical challenge and applied sense and reason to develop a practical, constructible and engineered solution, which benefitted all parties for the aforementioned Environmental, Commercial and Safety aspects. Meeting a tight construction programme at the front end of a long complex scheme gives Aarsleff great satisfaction. Scope of works 154 (No.) AZ26 steel sheet piles (section modulus 2600cm3/m of max length 8.0m) Integral enhanced toe support system comprising of 53 (No.) 254/254/132 S355 JO H-Section piles Prefabricated box section connection detailing at 1.26m centre to centre Construction period 21st July 2017 - 13th Sep 2017   For more information: Aarsleff Ground Engineering: +44 (0)1636 611140 | www.aarsleff.co.uk