Supply Chain - Site Preparation - Cofferdams
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Case Studies
- Holme Sluice Fish Pass Phase 2 (2024)
- Witches Oak Raw Water Pumping Station (2024)
- Gouthwaite Reservoir (2024)
- Seedy Mill WTW (2023)
- Tideway Central - Victoria Embankment (2024)
- Guildford STW (2023)
- Tideway West - Barn Elms CSO Connection Tunnel (2023)
- Lower Woodburn WwPS (2024)
- St Augustines Road Flood Alleviation (2023)
- Keadby Terminal Assisted Outfall Pumping Station (2024)
- Niagara Weir Stabilisation & Fish Pass (2023)
- Brook Street (Dawlish) CSO (2023)
- Meadow Road Stormwater Tank (2023)
- Guildford STW (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]
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.
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) 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]
(left) Works within the cofferdam in the Thames and (right) works ongoing within the cofferdam - Courtesy of Barhale[/caption]
Secondary lining works - Courtesy of Barhale[/caption]
(left) Commencement of shaft works, and (right) diversion works within Victoria Embankment -Courtesy of Barhale[/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) Excavation at the shaft base and (right) 2.5m ID tunnel excavator machine (TEM) being lowered into drive shaft - Courtesy of Barhale[/caption]
(left) Barn Elms shaft under construction and (right) the 2.5m ID tunnel excavator machine (TEM) being lowered into drive shaft - Courtesy of Barhale[/caption]
The TEM roll represents the machine’s rotation about its central axis and there was a continuous tendency to clockwise or anti-clockwise spin. To overcome the issue, inclinometers and laser targets were installed within the machine and used for base readings for roll calculation.
Installing the bespoke guidance equipment, and in-detail mapping of every stage of the drive, ensured that the TEM was able to operate effectively and carry out the pipe jack successfully.
A further challenge was the safe handling and maintenance of the 14 tonne, 3m diameter precast concrete jacking pipes. To address the issue, Barhale purchased a 20 tonne SWL welding roller to be used as a base stand so that the pipes could be rotated 360°. This solution enabled the team to inspect each pipe thoroughly without the need for access equipment and working at height.
It also brought a huge benefit in the preparation of the inter-jack stations. Using this system, the inter-jack hydraulic cylinders could be installed around the circumference of the jacking pipes by the fitters from standing position.
Overall, the use of the welding rollers saved the Barhale team time, eliminated the risk of working at heights, and reduced the number of lifting operations. This idea was nominated for a Tideway RightWay award.
Shaft cover slab under construction - Courtesy of Barhale[/caption]
(left) The probe drill in use, forward probing of the tunnel face before full excavation as part of the WPP and (right) temporary support from within the sacrificial outer skin of the TEM once the tunnel drive was completed - Courtesy of Barhale[/caption]
Once each concrete section had been broken out, the Barhale team could move in and pull the concrete from the invert back to the pit bottom for removal. Positioning the Brokk in advance of the shield meant that the removal of the material was not impeded.
Proceeding section by section, it took two and a half weeks to reach the TEM. Removal of the damaged lead pipe revealed that, under the pressure of sitting stationary in the ground for five months while the recovery strategy was devised and implemented, the tail skin of the machine had deformed more than anticipated.
By restarting and moving the TEM followed by the recovery shield forward into virgin ground, the Barhale team was able to relieve the pressure on the tail skin. This permitted the removal of the hood and the docking of the steel lead pipe after which the drive could be restarted.
Replacing the damaged reinforced concrete pipes created quite a challenge, but with the support of the project team, a pioneering solution to change the cracked pipes was developed. The recovery shield that Barhale developed not only enabled the damaged tunnel to be replaced but also enabled access to the TEM face where repairs and enhancements had to be conducted. Additionally, the purpose made tunnel shield was designed to allow complete dismantling upon completion of the tunnel drive, allowing the final connection to the main tunnel.
Secondary lining shutter in place within the sacrificial TEM outer skin at the junction of the main Tideway central tunnel - Courtesy of Barhale[/caption]
This consisted of a specialist automated tunnel formwork system that would ensure the tunnel secondary lining was constructed efficiently by pouring each section in one pass. This improved quality by reducing the number of construction joints compared to more traditional methods. As the equipment is fully automated, the hydraulic stop ends ensure a robust seal when pumping concrete. A mechanical travel system enabled quick set-up for each subsequent pour with minimal resources and it removed the need to manually strike and reconstruct formwork for each section of the lining.
Shaft cover slab under construction - Courtesy of Barhale[/caption]
Peter Leyton, Construction Director for the BAM Nuttall Morgan Sindall Balfour Beatty JV, praised the Barhale team for its hard work and effort in getting the TEM to the main tunnel connection:
Lower Woodburn WwPS site pre-construction - Courtesy of DAWSON-WAM Ltd[/caption]
3D models of new storm storage tank - Courtesy of RPS[/caption]
(left) CFA cased auger secant piling cofferdam installation and (right) excavation of storm tank exposing secant piles - Courtesy of DAWSON-WAM Ltd[/caption]
Aerial view of site during storm tank reinforced concrete base slab construction - Courtesy of DAWSON-WAM Ltd[/caption]
Single sided reinforced concrete wall pours against secant piles to form internal tank walls - Courtesy of DAWSON-WAM Ltd[/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.
[caption id="" align="alignnone" width="1200"]
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]
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]
(top) Collapsed left bank and masonry weir, (left) left hand cofferdam dewatered, exposing the extent of the undermining to the weir foundations, and (right) sewer pipes diverted through a temporary bridge (PortaDam and cofferdam installed on the left hand side of the river) - Courtesy of Ward & Burke[/caption]
(top left) Left bank foundation RC slab and wall built, excavator grab positioning reclaimed stone wall, (top right) left half of weir stabilised, shutter for right hand cofferdam installed, river bed graded ready for flooding, (bottom left) with the weir stabilisation complete the existing fish pass and part of the weir are demolished to make room for the new fish pass, and (bottom right) sewer pipes reconnected through the fish pass walls - Courtesy of Ward & Burke[/caption]
During construction, large stones from the collapsed downstream weir and left bank were recovered from the river. The design was altered to reuse these stones and incorporate them into the structure, avoiding embodied carbon associated with the original proposed concrete structures and imported aggregate. The stones were used to rebuild the left bank, installed as scour protection on the right bank, and used to landscape canoe landings. The stones helped the structure blend harmoniously with the surrounding environment.
Before flooding the left bank downstream cofferdam, a steel shutter was designed and installed on the new concrete slab to seal the proposed right bank cofferdam to the weir face. This enabled part of the right bank cofferdam to be constructed within the left bank cofferdam, ensuring a better seal and reducing risks associated with piling in the river.
Once the left bank was complete and the left half of the weir stable, the cofferdams were flooded and removed.
A similar process was followed on the right bank to stabilise the weir. Sheet pile cofferdams were installed upstream and downstream of the weir. Temporary pumps kept the cofferdams dewatered.
(top left) Propped cofferdam for upstream section of fish pass, preparing for blinding, (bottom left) fish pass wall rebar, upstream section, and (right) upstream baffles, penstock, and access metalwork installed in fish pass - Courtesy of Ward & Burke[/caption]
Midland Valves supplied a penstock upstream and stop logs downstream to isolate the fish pass for maintenance. The penstock and stop log frames were cast into the fish pass walls, flush with the base of the fish pass. This avoids grit being caught in the frame, preventing a tight seal.
The fish pass was constructed in two halves; upstream and downstream of the weir. The two sewer pipes were cast into the walls of the downstream section. The downstream section was constructed first so that the sewer pipes could be re-energised and the temporary pumping station decommissioned before the end of the whole project.
To construct the downstream section of the fish pass, a section of the weir and sewer pipes were removed. Then the ground was formed and blinded with a 8.53° slope. The base steel was fixed and the base poured. Next the wall steel was tied, shutters erected and the walls poured. The walls were constructed with a tolerance of +-5mm to ensure the baffles could fit and there wasn’t excessive space for debris to get caught. For the construction of the walls, the formwork panels had to be stepped to tie in with the run of the slope. The on-site joiners made relevant angled shutter bases to integrate with the main wall shutters so each wall could be poured in one go.
To construct the upstream section of the fish pass, a new cofferdam was installed. The cofferdam was initially propped with MGF frames. The blinding was designed strong enough so that the MGF frames could be removed once it reached strength. It was important that the MGF props were removed because they would have clashed with the fish pass wall, and limited lifting operations in the cofferdam. The construction process was repeated and the fish pass base and walls were poured.
Surveys and inspections of the fish pass by Yorkshire Water and the Environment Agency confirmed that the overall design and construction of the structure was satisfactory and within the design specification. On confirmation of this, the dewatering pumps were decommissioned and the sheet piles removed from the river to allow flows through the new pass.
A 160t crane was employed to remove the sheet piles upstream of the weir. The excavator that had driven them in could not reach over the new fish pass.
[caption id="" align="alignnone" width="1200"]
(left) right bank cofferdam, looking at the rebuilt left bank masonry wall (and right) 160 ton crane and vibro hammer removing the upstream cofferdam - Courtesy of Ward & Burke[/caption]
(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]
(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]
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]
Mini CS & Company News
- 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
- 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
- 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
- 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
- Stourport Cofferdam
Stourport CofferdamJ 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
- 21st July 2017 - 13th Sep 2017
For more information: Aarsleff Ground Engineering: +44 (0)1636 611140 | www.aarsleff.co.uk
