Audlem WwTW – Civil Engineering Works

Scope of Works

V J Donegan’s solution encompassed:

• Primary settlement & humus tanks
  Construction of 2 no. reinforced concrete primary settlement tanks and 2 no. 10.70m diameter humus tanks, with sloped bases, central hoppers, radiused walls and external launder channels – the humus tanks built within a 26m x 13m x 4.5m deep pre-driven sheeted cofferdam.
• Inlet works & grit removal
  New reinforced concrete inlet screens structure formed as three lanes with 1.5m high dividing walls to control flow, grit removal plant civils, and connection onto the live works inlet pipework with demolition of the existing pumping station once flows were diverted.
• Trickling filter & distribution chambers
  Reinforced concrete base and civils for the new 17m diameter trickling filter, interfacing with the precast filter package, plus the PST, trickle filter and humus tank distribution chambers and retaining wall.
• Shaft pumping station
  Under an earlier package on the same scheme, construction of the new 10.50m diameter segmental caisson shaft, sunk approximately 10m to formation with an underream, temporary works spanning an existing well, a 3.6m diameter internal chamber and benching – combining FFT pumping, storage and recirculation to eliminate intermediate pumping stations across the sloping site.
• Piling platforms & attendance
  Piling mats and crane pads, attendance on the bored piling contractor, and excavation and cropping of 60 no. piles beneath the PSTs and sludge tank.
• Pipework, drainage & ducting
  Approximately 95m of 200mm rising main, sludge main and potable water barrier pipe, a 2700mm diameter magflow and washout chamber, site drainage with 16 no. new manholes, and an extensive ducting network with 14 no. drawpits serving the new MCC kiosks, screens, grit plant, dosing kiosks and instrumentation.
• Kiosk bases, bunds & containment
  Bases and hardstandings for the MCC and chemical dosing kiosks, chemical blind tank and valve chamber, and chemical and sludge tanker delivery bunds constructed to United Utilities standard details.
• Access, reinstatement & handover
  A new concrete access road including a substantial cut and fill operation to achieve formation, french drains and soakaways, and full reinstatement, landscaping, topsoil and seeding.

Challenges & how we solved them

• Live-site working
  The works had to keep treating flows throughout. We carefully planned and carried out the connection onto the existing inlet pipework on live assets, sequencing work-fronts to maintain safe vehicle and pedestrian routes and demolished the existing pumping station only once the new flow routes were established.
• Topography & ground conditions
  The new inlet screens sit at the lowest point of the embankment, requiring engineered support to the excavation and stabilisation of the formation before construction could progress. Ground investigation indicated limited groundwater, and excavations were kept dry by sump pumping, with cut and fill earthworks to achieve the new access road formation and excavations taken into the existing batters while maintaining stable faces.
• Interfaces & tolerances
  Working alongside Offa-Fix Formwork on the concrete works, we coordinated closely with the precast trickling filter package, the mechanical screens, grit plant and scraper bridge installers, and the M&E contractor – providing attendances, crane accesses and sequencing around others so penetrations, builders’ work and duct positions landed first time.
• Programme
  Programme pressure was met head on, with the site team working extended hours and weekends at key stages to maintain progress for follow-on mechanical and electrical trades.

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