Supply Chain - Site Preparation - Shoring
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Case Studies
- Holme Sluice Fish Pass Phase 2 (2024)
- Seedy Mill WTW (2023)
- Gouthwaite Reservoir (2024)
- St Augustines Road Flood Alleviation (2023)
- Meadow Road Stormwater Tank (2023)
- Guildford STW (2023)
- Brook Street (Dawlish) CSO (2023)
- Hathershaw Fields CSO & Bardsley WwPS (2023)
- Keadby Terminal Assisted Outfall Pumping Station (2024)
- Witches Oak Raw Water Pumping Station (2024)
- Guildford STW (2024)
- WINEP Durham Transfers (2024)
Aerial view of the completed fish pass - Courtesy of Jackson Civil Engineering Ltd[/caption]
Modular wall shuttering in place for wall pour - Courtesy of Jackson Civil Engineering Ltd[/caption]
Excavated fish pass awaiting FRC works - Courtesy of Jackson Civil Engineering Ltd[/caption]
Non running fish pass mid-distance - Courtesy of Jackson Civil Engineering Ltd[/caption]
Completed fish pass - Courtesy of Jackson Civil Engineering Ltd[/caption]
(left) Completed fish pass looking towards the intake structure and (right) fish pass in operation showing control radial gate - Courtesy of Jackson Civil Engineering Ltd[/caption]
(left) Piling works for the RGF building and (right) construction progress March 2022 (photo by Lobster Pictures) - Courtesy of Galliford Try[/caption]
Clean water backwash tank, interstage pumping station and rapid gravity filter building - Courtesy of Galliford Try[/caption]
Interstage pumping station and rapid gravity filter building (from west) - Courtesy of Galliford Try[/caption]
Interstage pumping station and RGF building from the north - Courtesy of Galliford Try[/caption]
The Seedy Mill WTW project was faced with an extremely challenging regulatory target, by which point the new RGFs had to be in service. There were significant challenges with costs and programme, set against a backdrop of instability and unpredictability in supply chains and construction costs inflating at a much greater rate than CPI. However, Galliford Try and South Staffs Water’s proactive and collaborative approach to managing risk, delivered a project which was within the original target price, and the team met the regulatory date challenge with two weeks to spare.
Galliford Try’s construction management was key to the delivery of the Seedy Mill WTW project, and their collaboration with South Staffs Water allowed them to meet and surmount a significant number of challenges by careful planning, risk mitigation and challenging the programme whilst always maintaining focus of health, safety and wellbeing of personnel and the customer.
RGF pipe gallery - Courtesy of Galliford Try[/caption]
Interstage pumping station wet well - Courtesy of Galliford Try[/caption]
Pipe gallery
On the south wall of the RGF cells is a 71m long pipe gallery, which contains the backwash pipework system, the process outlet pipework system and the rinse pipework, used after the cell had a backwash but prior to the cell going into service.
Rapid Gravity Filter cells
The RGFs are housed in a cladded structure 71m long x 18m wide. There are ten cells built upon continuous flight auger piles, designed to take 10-15 MLD. The RGFs are concrete tanks, cast in situ using a mix of blending cement with fly ash to slow down the cure time and reduce thermal cracking and shrinkage.
On the floor of each cell is a Xylem Water Solutions Leopold underdrain flooring system (rather than the traditional nozzle approach), which provides improved bubble coverage and reduced installation time. Above the Leopold flooring are layers of sand and anthracite media.
Each cell has its own primary (ultrasonic) and secondary (level electrode) level measurement equipment as well as local control panels, turbidity monitor backboard, sample tap and differential pressure monitors. Access steelwork on top of the RGF cells allows access for maintenance of the associated equipment.
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RGF air pattern test - Courtesy of Galliford Try[/caption]
Clean Water Backwash Tank (CWBT)
The new CWBT was built in two compartments, fed by treated RGF process water. There are two 75kw pumps (duty/standby) per compartment, each capable of pumping up to 330 l/s, which flows back up through and cleans the filters. This is in conjunction with the blowers adding air into the system at various parts of the wash. The dirty backwash water is discharged in the existing waste systems.
Motor Control Centre (MCC) building
This building houses the new MCC contained in the IPS and CWBT drives and the main Programmable Logic Controller (PLC), which controls the operation of the IPS, RGF and CWBT systems. It also houses the two (duty/standby) air blowers that are utilised for backwashing of the filters.
Commissioning
The new IPS/RGF/CWBT arrangement was commissioned as far as practical offline. After successful dry testing, wet testing was conducted utilising process flow in but running all flow that had been through the RGF to waste until satisfactory water quality laboratory results and Site Acceptance Tests were achieved. Three cells at a time were turned into supply, in order to stagger the impact of bringing RGF cells online into the works. Each stage had a proving period, after which the core team would meet to review the results and then decide ‘Go’ or ‘No-Go’ for the next bank of cells.
Alfa Laval centrifuges - Courtesy of Galliford Try[/caption]
The new dewatering works had to be undertaken in the existing building around existing operational assets. A building extension was required to house the new Alfa Laval centrifuges and two screw conveyor systems from CTM Systems Ltd. However, the new polymer system and MCC were installed within the existing building, requiring careful planning to replace equipment in a phased manner with minimal disruption to the client’s process.
Dewatering area - Courtesy of Galliford Try[/caption]
Pontoon excavator - Courtesy of Mott MacDonald Bentley[/caption]
The design of the upstream leg of the siphon included a 70m length of 2000mm Ø flanged steel pipework leading from the inlet to the crest, with excavation of the reservoir bed to install at the designed depth necessary to attain the required submergence depth of the inlet end of the siphon. Excavated material could then be utilised as backfill and provide sufficient resistance to thrust forces about bends near the crest. Prior to passing through the crest, the siphon tapers from 2000mm Ø to 1600mm Ø.
Offloading pipes - Courtesy of Mott MacDonald Bentley[/caption]
Cofferdam installation around the concrete core - Courtesy of Mott MacDonald Bentley[/caption]
Working closely with Groundforce, MMB assessed different phases of the work and how the cofferdam could be optimised to suit construction requirements. The existing concrete core was utilised in the design to resist frame loadings throughout, alongside whilst the bottom frame was designed to be removed following the casting of the slab to facilitate further construction of the siphon.
Installation of the large diameter siphon pipes - Courtesy of Mott MacDonald Bentley[/caption]
Installation of the large diameter siphon pipes - Courtesy of Mott MacDonald Bentley[/caption]
Screenshot of Synchro software showing workings around the crest - Courtesy of Mott MacDonald Bentley[/caption]
Concrete core: (top left) before and (bottom left) after wire cutting with 82t of concrete removed, and (right) Reinstated concrete core following installation of 1600mm pipe prior to connection with the upstream leg - Courtesy of Mott MacDonald Bentley[/caption]
(left) The preferred option and (right) flooding on St Augustines Road - Courtesy of Galliford Try[/caption]
Outfall under construction - Courtesy of Galliford Try[/caption]
Poor ground and underfoot conditions adjacent to the River Rother proved too risky and problematic for traditional mobile crane lifts, so all lifts of the precast sections were to be undertaken with a tracked excavator. This further constrained the design and restricted the maximum mass of each section to 13 tonnes. Consequently, in its final iteration the precast headwall was designed in two sections and was combined with an in situ toe and infill slab/wall which completed the structural design.
(left) Installation of drive pit on St Augustines Road, (middle) guided auger bore rig, and (right) the transition between 600mm and culverts - Courtesy of Galliford Try[/caption]
Settlement calculations were undertaken using the “Guide to best practice for the installation of pipe jacks and microtunnels technique” and a predicted settlement of <3mm was deemed to be acceptable. The pre-condition surveys highlighted only minor cosmetic issues and were used as reference to the state of repair of the properties prior to construction work commencing.
The majority of the civil design was undertaken in house. This element included a design coordination role combining and processing the information received from the consultants and stakeholders. An example of the numerous stakeholders which were consulted is that of the Coal Authority. Initial searches indicated the presence of historical coal workings. More detail was sought and records indicated the presence of an adit within 20m of the proposed pipeline. A coal permit was sought from the Coal Authority and the design progressed whilst this was processed.
Service detection - Courtesy of Galliford Try[/caption]
Cofferdam and silt curtain - Courtesy of Galliford Try[/caption]
Cofferdam
A cofferdam was required to retain the River Rother and this was designed and supplied by National Trench Safety UK and installed by the primary subcontractor Arthur Civil Engineering. The cofferdam was unique in design in that it utilised Larsson piles in a trapezium shape (plan) to minimise over-dig yet still accommodate the headwall and first culvert.
The cofferdam was installed by Ivor King Piling using a 35t excavator with a Movax side grip pile driver attachment. The cofferdam was effective but 4” end suction pumps supplied by Selwood Ltd were still required to maintain the cofferdam and keep water levels low.
Headwall installation
Once the cofferdam was watertight, the headwall toe was cast in situ, after which the precast headwall arrived in two sections as planned. It was lifted into position by Arthur Civil Engineering using a 50t tracked excavator. An administrative issue led to the need to negotiate a 2-week FRAP extension with the EA and the headwall was completed and the cofferdam removed by 14 October in accordance with the conditions of the revised FRAP.
Pipeline works
Construction works on the remainder of the project continued in March 2022. A temporary one-way system was implemented to provide a safe working area to install the remainder of the pipeline with open cut works commencing on 14 March. The open cut works progressed steadily with over 100 services safely crossed. The later spring and summer months provided excellent conditions for online sewer relay with drought-like conditions, culminating in hosepipe bans for the majority of the UK.
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Open cut pipelaying - Courtesy of Galliford Try[/caption]
Prior to the tunnelling works commencing, concern was raised over the proximity of the tunnel as it crossed under a 225mm foul water sewer in Derby Road. With a clearance of just 300mm, the existing foul sewer was inspected by CPS Drainage Solutions using CCTV and a precautionary 5m cured-in-place patch liner was installed to strengthen the sewer prior to the guided auger bore operation. No-dig works commenced in early June and progressed well without incident and were completed towards the end of the summer. No settlement was detected during the installation and no visual deformations were reported from the nearby structures.
Open cut works continued late into the summer with flooding benefits delivered by 5 October. Significant rainfall events have since occurred and the feedback from residents previously affected by the flooding has been positive.
900mm Ridgistorm pipe from Polypipe Civils ready for installation - Courtesy of Galliford Try[/caption]
(left) Piling installation by Elite Sheet Piling Ltd, and (right) drainage blanket installation - Courtesy of Galliford Try[/caption]
(top left) 1200mm precast concrete pipe sections, (bottom left) backfilling the stormwater tank, and (right) Hydro-Brake® from Hydro International in flow control chamber - Courtesy of Galliford Try[/caption]
(left) Location of new sewage treatment works and tunnel route and (right) Slyfield Regeneration Project area - Courtesy of Adams Hendry[/caption]
RIC 1 and 2 pass areas - Courtesy of BAM Enpure Ltd JV[/caption]
This combined dataset is then used in Leapfrog 3D geological modelling software, which applies intelligent interpolations, and highlights anomalies that can be quickly assessed and removed. The resultant 3D model has then been used to enhance communication in the engineering AutoDesk BIM 360 federated models, and in the proprietary Arcadis SmartAtlas GIS viewer.
Rapid Impact Compaction (RIC) is a method of imparting energy to the ground using a repeated but relatively short drop-weight, where a base plate (or “puck”) is in constant contact with the ground. RIC is preferred over a larger drop-weight technique due to its more progressive and less disturbing impact on the ground it is being used on. The method is also faster and uses smaller scale setups. A challenge for the RIC method was whether the energy it imparts is sufficient to densify the ground, versus other higher energy drop-weight methods. A trial was deemed necessary to demonstrate the suitability of this method. RIC is proposed to be applied over the majority of the site with an expected densification of landfill down to approximately 4.5m. Areas where assets will not be supported on driven full depth piles will undertake a second pass of the RIC method, reducing the long-term settlement of the landfill material. The predicted reduced surface will be levelled as required by the infill of depressions with imported stone or other suitable material.
Improvement of the existing ground by reinforcement through installation of Vertical Rigid Inclusions (VRI) method across the site. Supporting of level sensitive and heavier elements will be on precast driven piles founded below the landfill material. The combination of methods will be designed to achieve Thames Water’s settlement performance values over 40 years, and remain within the allowable values of 50mm and 100mm. This will reduce the need for full depth driven piling which would otherwise be required.
Reduction of infiltration to the landfill materials by ensuring impermeable surfaces drain to the treatment works and are released at the outfall away from the site. Gas and leachate well monitoring is provided along the perimeter of the site to monitor any impact and provide leachate removal points if required.
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(left) Rapid impact compaction rig and (right) pile under test - Courtesy of BAM Enpure Ltd JV[/caption]
(left) inlet pumping station physical model and (right) inlet pump testing physical model - Courtesy of Hydrotec Consultants Ltd[/caption]
The pump design has been developed to fulfil the project brief load requirements (future peak IPS capacity 2585l/s) and some flexibility either side of the requirements is available due to the standard capacity equipment design offered from the supply chain.
The proposed arrangement now consists of a wet well 12.5m diameter, approximately 20m deep. A common inlet will be provided to dissipate any entrained air, and two selectable pumped sections with double isolation will be provided by wall mounted penstocks on full height walls.
The pumping well will be constructed in two halves, hydraulically connected in normal operational mode however each half will be able to be isolated (using motorised penstocks) in accordance with specification requirements surrounding double isolation, to allow person entry into half of the wet well at a time.
Each half of the wet well will have three pumps installed giving a capability to provide full flow to treatment from two pumps with a standby permanently installed.
The pumping station was first modelled by computational fluid dynamics (CFD) to demonstrate the assumed flow patterns that will occur. The pumping station was then physically modelled to comply with the specification and process design requirements particularly with respect to distribution, mixing, settlement, turbulence, dispersion, and freeboard for the full range of flows that each structure is expected to receive.
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Storm overflow physical models - Courtesy of Hydrotec Consultants Ltd[/caption]
Inlet works
The inlet works is being designed to receive all pumped flows from the inlet pumping station (including future peak IPS capacity 2585 l/s), inlet works drainage and screening liquor return flows. Flows will enter the inlet works and then separate across the four escalator screens inclined at an angle of 45°. Each screen will be provided with a local proprietary control panel. Each panel will incorporate a differential ultrasonic level control.
An emergency bypass will be provided upstream of the screens to accommodate all four screens blinding at the same time. Three 1200mm wide duty screens will be required to screen flows from low flow up to 2585 l/s, screening 6mm in two directions.
The inlet works and grit treatment plant will be covered with odour covers which will be connected to the inlet works and PST odour plant. The inlet works has been classified as a Zone 2 Area under the odour covers and all equipment beneath the odour covers will be ATEX rated.
Storm tanks
Storm flows from the inlet work storm separation chamber will flow into two storm tanks via a 1400mm above-ground pipe. Within the 1400mm pipe between the storm separation chamber and the storm tanks there will be a partial pipe MCERTs certified flow meter to measure the total flow into the storm tanks.
During normal operation the blind tank will fill first, then the spill tank will fill. In the event that both tanks are full to capacity (and still in storm flows) the spill tank will overflow via a weir and the storm tank will discharge to river.
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Elevated inlet works - Courtesy of BAM Enpure Ltd JV[/caption]
The storm tanks contents will automatically return to the inlet pumping station via 700mm gravity pipe when the flow being pumped to the inlet works drops below a predetermined set point. The return flows will be controlled to approximately 0.5 DWF via an automated valve controlled by an electromagnetic flow meter located in the gravity main, returning to the common inlet well of the inlet pumping station.
Storm tank cleaning will be a pumped system with the two pumps located external to the storm tanks. Storm tank cleaning will be initiated during the latter part of the storm tanks draining back to the inlet pumping station and will not operate when the tanks are filling. The pump discharge pipe work will include connections for flushing with washwater.
Ferric storage & dosing
Two 45m3 ferric storage tanks will be located in a concrete bund with the dosing skid packages and control system located within an adjacent kiosk. The bund will be capable of containing 110% of the one of the storage tanks plus 10% allowance for rainwater. A drive-in bunded area for chemical deliveries will be provided and an underground chemical interceptor will contain any local spillages, complete with a Castell interlocked 3-way valve to allow the bunded drainage area either to drain into the interceptor (during a chemical delivery) or to drain into the site drainage (normal operation).
Chemical dosing points will be provided upstream of the PSTs, on the common outlet channel of the ASP, and upstream of the tertiary treatment plant. The dosing points will utilise sparge systems to ensure adequate distribution of chemicals into the channels.
Odour control plant
The odour plant is a 2-stage system. Stage 2 filters will discharge into an 18-metre-high odour stack. The plant has been designed to achieve a minimum removal efficiency of 98% of H2S and 99% removal of odour, based upon a total system duty of 8432 m3/hr (of which 4813 m3/hr is from the inlet works and 3619 m3/hr from the primary settlement tanks).
Service water
A potable water main supplies a service water break tank via a ballcock (float valve). The service water break tank has a working volume of approximately 30m3 which gives a nominal retention of approximately three hours at average throughput. Service water booster pumps draw water from the tank and transfer it to the service water main network where it feeds the polymer make-up system for all thickeners and dewatering belt presses.
Primary settlement distribution chamber
The distribution chamber has been CFD modelled to calculate the flow split to each downstream primary settlement tank from first principles, and assess whether the proposed design would deliver an equal flow split (+/-5%) for seven future flow scenarios. This required the inlet bellmouth to be turned down to improve flow splitting.
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PST distribution chamber CFD models: (left) with four PSTs in service and (right) with six PSTs in service - Courtesy of The Fluid Group[/caption]
Primary settlement
Primary settlement consists of four 47.15m long by 10m wide tanks, with a depth ranging between 6.24m at the hopper end and 5.3m at the outlet length (equating to 1 in 50 floor slope). Each PST tank has three sludge hoppers at the inlet end. The outlet of the PST discharges into a common 1000mm wide outlet channel. From this outlet channel the 1000mm outlet pipe from the drop box combines with the 700mm RAS lines into an above-ground 1200mm pipe.
Retractable odour covers will be provided across the PST tanks to allow for future inspection, cleaning and maintenance. The odour covers will be connected via ducting to the inlet works/primary settlement tank odour plant. All mechanical equipment installed below the covers will be constructed from 316 stainless steel or high performance plastics. The primary settlement tanks have been classified as a Zone 2 Area, and all electrical equipment beneath the odour covers will be ATEX rated.
The design of the PST Tanks is based upon a maximum inflow of 3022m3/hr to all four in-service tanks, and a peak flow to each tank of 1007m3/hr with one PST out of service. In normal operation all four PST tanks will be in service.
Within each PST tank a chain and flight scraper system will be provided which will utilise high-tech non-metallic materials as the main materials of construction. Scum from the primary tanks will gravitate via a rotating surface skimmer pipe to the above-ground primary settlement scum tank. The primary scum return pumps are progressive cavity pumps, operating in a duty standby configuration. The pumps are fixed speed pumps operating between a high and low level in the scum tank.
The PST sludge hoppers will desludge based upon a SCADA-adjustable interval and duration. The primary desludge pumps are progressive cavity pumps, operating in a duty/standby configuration. The pumps are variable speed pumps operating to maintain a SCADA-adjustable flow set point.
Once the effluent has flowed through each PST it will enter into a common 1000mm wide outlet channel. From this outlet channel flows transfer to the ASP distribution chamber via a drop box and 1000mm above-ground pipe.
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ASP overview - Courtesy of BAM Enpure Ltd JV[/caption]
Activated sludge plant
The ASP plant will have a distribution chamber using the same general arrangement as the primary settlement distribution chamber.
The activated sludge treatment tank consists of four ASP lanes. Each ASP lane has a selector tank followed by an anoxic zone and then the three aerobic zones. The main aeration lane will be fitted with aeration pipework and fine bubble diffusers. The aeration vessel is 80m long and 6.1m wide with a water depth of 7.05m. The total instantaneous maximum air demand of the ASP is 10,438 m3/h.
The first third of the aerated fraction of each lane will contain 50% of the aeration capacity, the middle third 30%, and the final third 20%. Each aeration lane will have three passes, arranged as channels of 6.15m width. The air for the diffuser grids will be supplied from three ASP air blowers operating on a duty/assist/standby basis. The aeration system will be controlled by an ammonia based real time control (RTC) system utilising a feed forward ammonia load input and a feedback ammonia concentration.
Once the effluent has flowed through each ASP lane it enters into a common 1000mm wide outlet channel. From this outlet channel flows transfer to the FST distribution chamber via a drop box and 1200mm above-ground pipe.
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Anoxic and aeration zones flows - Courtesy of BAM Enpure Ltd JV[/caption]
Final settlement tanks
The FST plant will have a distribution chamber using the same general arrangement as the primary settlement distribution chamber. The four FSTs will consist of 32m diameter flat bottomed circular tanks with a side wall depth of 6.15m. The FST will separate solids from the flow via settlement, producing a clarified effluent which overflows a peripheral weir into a launder channel, before gravitating to the tertiary treatment distribution chamber via a 1000mm below-ground pipe.
The combined clarified outlet flow from the four tanks will be monitored by a common flow meter, as well as suspended solids and phosphorus monitoring instrumentation, all provided on the common line to tertiary treatment.
The design of the FSTs is based upon a maximum inflow to each tank of 1741m3/hr with one FST tank out of service. In normal operation all four FST tanks will be in service. Each tank will have a 700mm inlet pipe, which will flow into a central diffuser drum before entering the FST tank. Each tank features a 600mm outlet pipe fed via a peripheral launder channel, as well as a 400mm RAS gravity outlet pipe. Each of the four tanks features a full bridge rotating scraper system which will run continuously in normal operation.
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32m final settlement tanks & sludge return (RAS pumping station) - Courtesy of BAM Enpure Ltd JV[/caption]
Sludge return (RAS/SAS pumping station)
Sludge from each pair of FSTs will enter one of two RAS/SAS desludge chambers. The two chambers will be located side by side and will share a set of three duty/duty/standby RAS transfer pumps, which will recycle the settled sludge from both RAS/SAS desludge chambers to the activated sludge plant distribution chamber feed line.
The variable speed centrifugal RAS transfer pumps will be capable of pumping 2200m3/hr at a maximum head of 8.9mhd. The pumps will operate between high and low level in the duty RAS/SAS desludging chamber, with both chambers provisioned.
A pair of duty/standby SAS pumps is provided, which will facilitate wastage of surplus sludge, with each pump drawing from a single RAS/SAS desludge chamber. The fixed speed centrifugal pumps will transfer sludge to the SAS buffer tank. Control of the SAS pumps will be carried out either on a timer or based on the level in the SAS buffer tank, with the common discharge line featuring flow monitoring.
Tertiary treatment
Clarified effluent flow from the FSTs will pass to the tertiary ferric mixing and flocculation (post-precipitation) stage, where the option will exist to dose ferric sulphate solution into the flow in order to encourage flocculation of remaining solids. This stage will be split into two parallel streams, with flow from the FSTs initially entering via a single bellmouth inlet into a common inlet channel, before passing via twin overflow weirs into two rapid mix chambers, and subsequently overflowing into two flocculation chambers. The design of the rapid mixer chambers will ensure complete mixing (>95% CoV) of chemical in less than 4 seconds.
Flow from the flocculation chambers will weir into a common outlet channel leading to a flow distribution chamber feeding the tertiary treatment stage.
The distribution chamber has been CFD modelled to calculate the flow split to each downstream cloth pile filter from first principles, and assess whether the proposed design would deliver an equal flow split (+/-5%) for seven future flow scenarios.
The tertiary treatment stage will comprise six cloth pile filters, which will operate with all filters in service - however the peak flow will be able to be treated with only five filters in service. The filters will be sized to accommodate a peak flow of 840 l/s, producing a final effluent of 20 mg/l TSS (95%ile) and 0.2mg/l TP (average).
Bypass pipework is to be provided adjacent to the cloth pile filter structure, by which clarified effluent from the FSTs may bypass the tertiary ferric dosing/flocculation and cloth pile filter stage.
Each of the six cloth pile filters will feature a central rotor drum onto which filter discs are attached. The rotor and discs will be fully submerged within the tank, with the discs supporting the physical cloth filter media. Flow entering the filters will flow from outside the discs through the cloth into the discs’ interior, with solids collecting on the external surface of the cloth pile, creating a headloss. As this headloss increases, the water level in the tank will rise and at a pre-set water level (as detected by an ultrasonic level sensor) a cleaning cycle will be initiated.
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Tertiary treatment flocculation chambers: Eliquo Hydrok Mecana cloth pile filters - Courtesy of BAM Enpure Ltd JV[/caption]
Filtered final effluent (FFE) from the inside of the filter disc and rotor drum assembly will pass forward through the unit via a low-level aperture to an outlet chamber, from which flow will weir into the common final effluent outfall chamber. An emergency overflow weir is to be provided, allowing unfiltered effluent from the filter tank (external to the discs) to weir over into the outlet chamber.
Backwash liquors from the backwash pumps will exit the filters via a common manifold, draining by gravity to the grit plant liquor PS. Eight backwash pumps will be provided per machine, giving a total of 48 pumps across all six machines. The pumps will be submersible units placed within the tank, with each pump being dedicated to three filter discs. The backwash flow rate is rated for 10 l/s (subject to the installed pipework design/headloss).
Each of the six filter tanks will see some solids settlement occurring (and potential accumulation of other debris), which will create a build-up of sludge in the bottom of the tank. This sludge will be periodically removed by a set of two duty/standby sludge pumps per machine (i.e. 12 sludge pumps installed in total). The discharge from each sludge pump will be connected to the common backwash manifold, leading to the grit plant liquor pumping station.
Final effluent discharge
Flows leaving the cloth pile filters will pass out from the main filter chamber via a low level aperture into a small outlet chamber, from which flows will weir over into the common outfall channel. The final effluent (FE) will flow under gravity through an FE flow measurement flume, with an ultrasonic instrument for measurement of final effluent flows discharged to outfall.
The FE outfall channel will feature a pipe leading to the FE washwater system, with a further line branching off this pipe servings as the suction line for FE Meteorburst Analyser. On exiting the FE outfall channel, flows will enter a dedicated FE outfall main, which will drain by gravity, discharging to the river north of the STW site.
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New Guildford STW: 3D model night-time overview - Courtesy of BAM Enpure Ltd JV[/caption]
Thickened sludge blending tanks - Courtesy of BAM Enpure Ltd JV[/caption]
Each tank will feature separate inlet connections for the three types of sludge being received, with actuated valves and crossover lines allowing all sludges to be directed to either of the two tanks. The tanks will also feature outlet actuated valves, which will allow either tank to be isolated from the sludge belt press feed pumps downstream, thereby ensuring the pumps only draw from a single tank at any given time.
A set of three duty/duty/standby sludge belt press feed pumps will be provided, which will transfer blended thickened and imported sludge from the thickened sludge blending tanks to the sludge belt presses. The pumps will be variable speed progressive cavity units, with a peak capacity of 30m3/h (i.e. 15m3/h per pump) at a maximum head of 48.5m, based on sludge of up to 7.0%DS.
Dewatered cake leaving each belt press will enter a discharge cake hopper leading to the suction end of a sludge cake pump. Three pumps will be provided, with a single pump dedicated to a single machine; each pump will operate in conjunction with the associated belt press upstream.
The pumps will be variable speed progressive cavity units, with a peak capacity of 7.4m3/h of sludge (up to 30%DS). The pumps will transfer the cake via individual discharge lines to the sludge cake silos, with manual discharge crossover facilities allowing sludge from the pumps to be directed to either of the two silos as required.
Cake silo storage & discharge
Dewatered sludge cake will be pumped to two truck-loading cake silos, with a combined storage capacity of 600m3, sized to provide 7-days of storage at average cake production. Each silo will feature a discharge screw conveyor (with a sliding frame ‘anti-bridging’ device) which will discharge the cake through a hydraulically operated slide gate valve.
Odour control plant
The odour plant will be a 2-stage system. Stage 2 filters will discharge into an 18-metre-high odour stack.
The plant has been designed to achieve a minimum removal efficiency of 98% of H2S and 99% removal of odour, based upon a total system duty of 6629m3/hr, extracted from the various tanks and thickening/dewatering machines in the sludge plant area.
(left) Outfall route plan - Courtesy of Bam Enpure Ltd JV, and (right) outfall low flow scenario CFD model - Courtesy of Arcadis[/caption]
Outfall structure
The outfall structure will consist of a reinforced concrete headwall, set back from the river channel, to be founded in the river terrace deposits and flared to direct flows downstream and minimise the impact of upstream debris from collecting. The headwall will have duckbill valves on the discharging pipes, and erosion control products utilised in the surrounding area to tie the headwall into the natural riverbank and bed.
The erosion mattress employed following the headwall structure will provide a secondary point at which turbulent flows can dissipate energy without eroding the natural bed of the river.
Where the headwall ties into the natural riverbank, the hard/soft interaction between headwall and natural soil will be reduced by the installation of Rock Rolls erosion control and willow stakes at the base, and the installation of a natural hydro-seeded CocoBN blanket or equivalent (to be seeded with local seed varieties) which will retain the slope shape until vegetation establishes and provides an effective natural erosion control. This will also provide a gradual slope to access down to the river.
(left) Flow control chamber showing overflow weir and Hydro-Brake® and (right) looking down into the 30m3 stormwater tank showing the float controls, pump, pump guides and sump - Courtesy of Galliford Try[/caption]
(left) All weather kiosk constructed off-site, containing the alarms, telemetry, pump return and mains in-comer and (right) access cover within the Manor House Car Park into the 30m3 stormwater tank all completed day before handover - Courtesy of Galliford Try[/caption]
Completed car park area day before handback - Courtesy of Galliford Try[/caption]
CSO chamber with at Hathersaw Fields with overpumping pipework - Courtesy of VJ Donegan Civil Engineering Ltd[/caption]
Exposed CSO chamber at Hathershaw - Courtesy of VJ Donegan Civil Engineering Ltd[/caption]
(top left) Temporary access road, (bottom left) collaborative working, and (right) aerial view of the Hathershaw CSO site compound - Courtesy of VJ Donegan Civil Engineering Ltd[/caption]
Before work could take place in the CSO chamber it was necessary to set up a system of over pumping from one chamber to the other. A safety monitoring system was later installed which included an alarm which would sound at times of heavy rain, acting as an early warning system for the team working within the chambers to ensure they could carry out work safely.
Following the installation of the new powered screens and several tests it was necessary to modify the existing chamber adjacent to the CSO. In order to undertake this work successfully, sheet piling was installed prior to the modifications. This work was completed within 6-weeks, ensuring that the newly installed powered screens were correctly sized. Water Engineering Services Ltd was the mechanical and electrical sub-contractor responsible for the screen installation. Following completion of this work the temporary ramp was removed and the site reinstated.
(left) Bardsley CSO chamber - Courtesy of Costain, and (right) the Bardsley precast cover slab - Courtesy of VJ Donegan Civil Engineering Ltd[/caption]
Outfall construction (November 2021) - Courtesy of GBJV Ltd[/caption]
Outfall construction constraints - Courtesy of GBJV Ltd[/caption]
Aerial view of final pour - Courtesy of GBJV Ltd[/caption]
Pump hall - Courtesy of GBJV Ltd[/caption]
Outfall structure including fenders - Courtesy of GBJV Ltd[/caption]
Installing the floating wetlands - Courtesy of Matthew Nichol Photography[/caption]
Floating wetlands (2023) - Courtesy of Matthew Nichol Photography[/caption]
Pumping station refurbishment - Courtesy of Sky Revolution[/caption]
River intake - Courtesy of Sky Revolution[/caption]
Installed wetlands - Courtesy of Sky Revolution[/caption]
The 31 constructed wetlands use naturally occurring biological processes to contain and treat ammonia, suspended solids and trace metals. Coupled with installing ceramic membranes at Witches Oak WTW (to provide a filtration barrier, reduce turbidity and remove pathogens such as cryptosporidium), the project is a more carbon-friendly treatment solution.
A screenshot of the 3D model used for design and construction - Courtesy of Bam Nuttall Ltd[/caption]
Construction of the high level inlet works structure - Courtesy of Bam Nuttall Ltd[/caption]
(left) Rapid impact compaction underway and (right) a selection of site plant in use - Courtesy of Bam Nuttall Ltd[/caption]
(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.
(foreground) Ferric mixing and flocculation chambers and (background) concrete bases for sludge tanks - Courtesy of Bam Nuttall Ltd[/caption]
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]
Activated sludge plant precast walls erected, prior to pouring base slab and concrete stitches - Courtesy of Bam Nuttall Ltd[/caption]
(foreground) PST precast walls with concrete stitches and bases and (background) ASP precast walls - Courtesy of Bam Nuttall Ltd[/caption]
Safdar Ali, Andrew Dawes and Izhar Ahmad from the BAM team at the completion of the tunnel - Courtesy of Bam Nuttall Ltd[/caption]
Threading buried process pipework between new structures requires extensive temporary works - Courtesy of Bam Nuttall Ltd[/caption]
(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]
Piling operations by Francis & Lewis International Ltd, for the construction of the pipe bridge substructure - Courtesy of Esh-Stantec[/caption]
Active Tunnelling constructing the new wet well shaft at Pity Me STW
Construction of new valve chamber and associated pipework at Pity Me STW - Courtesy of Esh-Stantec[/caption]
Aerial view of working area at Brasside STW - Courtesy of Esh-Stantec[/caption]
Construction of pipe bridge structure by Francis & Lewis International Ltd - Courtesy of Esh-Stantec[/caption]
Mini CS & Company News
- Derby Hydro Power House
Derby Hydro Power HouseScope of works
The purpose of the job was to design and supply temporary and permanent support for a hydro power house and turbine chamber (plus associated inlet channel and tailrace) constructed at the side of an existing weir on the banks of the River Derwent in the centre of Derby.Issues & solutions
The design incorporated a single level of modular 406UC Hydraulic Brace system in conjunction with Larssen piles up to 10m in length, toed in mudstone, covering a perimeter of over 150m. MGF's design allowed early removal of the brace by using a permanent concrete base slab as a low propped cantilever. The design had to take into consideration the complicated construction sequence; and the location of a large crane during installation and removal of the river piles. During the project Balfour Beatty and MGF collaborated to develop the Stairsafe system (the UK's first temporary steel stair system designed specifically for excavations). The system proved a great success in providing rapid and safe access into excavations leading to greater site productivity. The system is now being used throughout the UK on excavations up to 6.5m in depth. [caption id="" align="alignnone" width="1200"]
Courtesy of MGF Ltd[/caption]
Project details
- Sector: Energy & Waste
- Client: Derby County Council
- Contractor: Balfour Beatty
- Consulting engineer: Atkins
- MGF Depot: Midlands - Rugeley
- Product hired: 406UC Hydraulic Brace, 10M Larssen Piles
From early in the tender process MGF have been heavily involved with Balfour Beatty to develop an innovative, cost effective and highly complicated cofferdam design; which helped make Balfour Beatty's tender attractive to the client, Derby City Council. Michael Rummens, Balfour Beatty Site Agent, commented:The verdict
"MGF were brought in at tender stage to assist in the value engineering of the cofferdam and support frames. Upon contract award, MGF's technical team were extremely proactive in producing a workable design in line with the projects requirements. The professional, amenable and expedient attitude continued throughout the process from design, technical support, plant hire and delivery and site assistance."
For more information: MGF Ltd | +44 (0)1942 402700 | www.mgf.co.uk
- Major Supply Grid Upgrades, Somerset
Major Supply Grid Upgrades, SomersetScope of works
Excavation works began in 2017 at the Dancing Hill Reservoir site as part of a £6 million project to upgrade the Water Supply GRID for Bridgwater and the surrounding areas. Major upgrades are required due to large-scale developments in the area.Issues & solutions
The design was particularly challenging due to the complicated nature of the ground surrounding the reservoir tank. A sizeable berm was built on the ground profile around Cofferdam 4 to ensure a safe and stable excavation. This exaction also had to accept other loadings from Cofferdams 1, 2 and 3. Multiple 203UC tank brace frames were used due to the strict lift plan limit of 1 tonne. Larger or heavier brace systems could risk the collapse of existing foundations. Vibration pile driving was not permitted due to the detrimental effect it could have on the high-pressure water mains that supplies customers. There was also a HV cable running through the site that had to be avoided. The exact location of other services created additional challenges and ongoing surveys had to be monitored throughout the duration of works. As of 2017 there are four connected cofferdams in place allowing safe working space to combine new pipeworks to the main reservoir tank. Multiple back-to-back 203UC tank braces with special alignment of bracing has been key in the design, combined with KKD 600 sheets to secure the trench. Several Lightweight DavitSafe systems allow safe access into the 10m deep cofferdams.- Sector: Water & Utilities
- Client: Wessex Water
- Location: Bridgewater, Somerset
- Scheme: Water Supply GRID Upgrade
- MGF depot: Bristol
- Products hired: Multiple 203UC brace, KKD 600 sheets, lightweight davit
Dancing Hill - Courtesy of MGF Ltd[/caption]
For more information: MGF Ltd | +44 (0)1942 402700 | www.mgf.co.uk
- Alleviating Flooding at Beaumaris Castle
Alleviating Flooding at Beaumaris Ca...The project required the contractor to excavate within 25m of Beaumaris Castle – a UNESCO World Heritage site and one of the best examples of 13th and 14th century architecture in Europe attracting over 100,000 visitors last year. Faced with the challenge of installing 600m of 1.5m diameter polypipe in 6m sections between existing manholes, John Kelly Construction spent time researching the products available on the market, before finding that MGF’s High Clearance Trench Boxes were ideal for the job. [caption id="" align="alignnone" width="1200"]
Courtesy of MGF Ltd[/caption]
The 7m x 2.9m wide High Clearance Trench Boxes coupled with Top Boxes saved time and money to the contractor when compared to sheets and frames. The strength of the box allows suitability and capability of going to 5m depth and having high clearance struts on both ends of the box allows access at both sides – ideal for installing larger diameter pipes.
[caption id="" align="alignnone" width="1200"]
Courtesy of MGF Ltd[/caption]
Paul Cowen, Technical Sales for MGF commented:
“Beaumaris’ most recent floods in 2017 was the catalyst that something needed to be done regarding the surface water drainage system. MGF became involved to supply the excavation support equipment to alleviate the threat of flooding to protect the natural beauty and tourism trade in the area”.
MGF’s stock logistics team confirmed availability of the kit at our Dartford depot and coordinated transfer to the Astley depot before delivery to site with three 40ft articulated vehicles and two 15t wagons to ensure the order was met. [caption id="" align="alignnone" width="1200"]
Courtesy of MGF Ltd[/caption]
John Kelly, Managing Director of John Kelly Construction, stated:
"I was very impressed with MGF as a company as they were very quick to respond to our queries, provided designs and all equipment ordered arrived on site with no delays."
- Sector: Water & Utilities
- Client: Isle of Anglesey County Council
- Contractor: John Kelly Construction
- MGF depot: North West - Astley
- Products hired: High clearance trench box, top boxes & titan manhole box
For more information: MGF Ltd | +44 (0)1942 402700 | www.mgf.co.uk
- Double Slide Rail Installation at SmartParc Development, Derby
Double Slide Rail Installation at Sm...NTS UK were first contacted by KPM Contracting in February 2023 with regards to providing a ground support system for a 13m x 3m foul pump tank to be installed at 5.5m below ground level. NTS UK provided a ground support system utilizing their Double Slide Rail tie-back system to provide a clear internal opening of 14.2m x 4.2m. Since the successful installation of the first foul pump tank NTS UK have gone on to provide the ground support solutions for an additional nine tank installations undertaken by KPM across the site. These excavations ranged from double tank installations at 20m x 15m plan dimensions to manhole installations 3.5m x 3.5m in plan with incoming services on three sides accommodated by the NTS UK pile chamber solution. The ground support systems utilized at the site incurred a number of challenges including high and variable groundwater, varying ground conditions, tight programme, unknown existing infrastructure and the neighbouring River Derwent. NTS UK were able to provide a design solution using their Slide Rail System. Many of the tank excavations were designed to allow for the re-use of components between different excavations, cutting down on transport, therefore reducing the carbon footprint attributed to each excavation. Fewer components than traditional shoring systems are used with the NTS UK Slide Rail system, this ensures fewer lifting operations and a much quicker and safer installation method. The system was installed using the dig & push method of installation which allows for no eccentric vibration and a no-toe solution, ensuring the risk of impacting any unknown services was mitigated. [caption id="attachment_1914" align="alignnone" width="1200"]
(left) First tank being lifted into the open excavation and (right) twin tank Slide Rail excavation 20m x 15m x 4.5m - Courtesy of NTS UK Ltd[/caption]
One of the larger 20m x 5m x 4.5m excavations at the site was close enough to the River Derwent for a sheet and frame solution to be considered. NTS UK’s temporary works designers deemed that an excavation this size at the site required 85 (No.) 7m Long Larssen Piles with two levels of the NTS UK System 80 frame. In contrast the NTS UK Slide Rail System utilized for the construction of the ground support system consisted of fewer than 50 components. The absence of any frames has also resulted in concrete/material, and therefore environmental and cost, savings for KPM Contracting. The components from this excavation were then utilized on two other excavations at the site. KPM Contracting were able to excavate, install & backfill the 20m x 5m x 4.5m excavation in seven working days – far quicker than would have been possible when using traditional methods, highlighting the environmental & commercial benefits of the system.
NTS UK’s Slide Rail is becoming ever popular in temporary works circles as the preferred method for fast, safe, cost-effective temporary excavation solutions.
Martin Munnelly, director of KPM Contracting.
“The system is so easy to use, far quicker, much safer and reduces our material costs significantly. It will definitely be explored for all future excavations,”
Geoff Bates, Area Sales Manager NTS UK.“The guys on site have been brilliant, and have all fully embraced the system.”
For more information contact National Trench Safety: 03332 076 007 | https://www.ntsafety.co.uk/
- River Humber Pipeline Replacement
River Humber Pipeline ReplacementScope of works
National Grid, working with North Lincolnshire Council and East Riding of Yorkshire Council, developed a plan to construct a tunnel under the River Humber to replace the existing pipeline. The three-year project will provide National Grid with a 5km long, 3.65m diameter tunnel bored 30m under the river bed. A single 1200mm concrete-weight coated steel pipe will be inserted into the tunnel in a single string, making it the longest gas pipeline insertion of this kind in the world.Issues and solutions
The River Humber pipeline is an important pipeline - connecting an import location for gas at Easington, on the East Yorkshire coast, to the national network – delivering gas supplies to millions of households throughout the UK. The original pipeline, Feeder 9, is buried in a cut-and-cover trench under the river bed where tidal patterns have eroded the river bed uncovering the pipeline. Remedial work was undertaken to provide a short-term solution while a long-term solution was developed. Working with the joint venture consisting of Skanska, PORR Bau GmbH and A.Hak, MGF’s in-house design engineers developed and manufactured a bespoke temporary works propping solution for the tunnel boring machine (TBM) launch pit excavation. The contractor required the design to allow for the following key factors:- Use of a load monitoring system.
- Design of bespoke connection details to sheet piles or capping beams where steel walers were not used.
- Design of bespoke 'headwall' beam to eliminate knee bracing at the end of the tunnel portal to increase working space.
- Design of prop connections to withstand 10 tonne accidental load.
"This project was particularly challenging due to the multiple levels of framing, high loads and strict robustness criteria. As the design was required to survive the loss or damage of a prop and withstand a 10-tonne impact load more props were required, however we had to balance this with ensuring that the contractor had sufficient space to excavate efficiently. The design of the headwall beam contributed significantly to this as it removed the requirement of having knee bracing at the end of the excavation, opening space and making bulk excavation easier."
The project will take approximately two years to complete and top level of the temporary works will stay in place during this time. In an adjoining field, the pipework is being welded in top strings in readiness for insertion. The tunnelling is currently underway with a slurry TBM.
For more information: MGF Ltd | +44 (0)1942 402700 | www.mgf.co.uk