MGF assists with the installation of upgrades to Mile Oak Sewage Treatment Works

  • Project Mile Oak Sewage Treatment Works
  • Client Severn Trent Water
  • Principal Contractor JN Bentley
  • Project Lead Rob Eagles, Regional Engineering Manager
  • Key Benefit A cost effective and carbon saving temporary works solution
Case Study Image


The purpose of this project was to upgrade the existing sewage treatment works at Mile Oak in Shropshire. This included the construction of a new activated sludge plant (ASP), final settlement tank (FST), tertiary solids removal plant, ferric dosing plant and all associated pipework.

MGF engaged early in the design phase through an existing relationship with the team at Mott Macdonald Bentley (MMB). Once the conceptual designs for the ASP and FST were complete, a Microsoft Teams meeting was arranged to discuss the proposals and notably the interaction between temporary and permanent works in further detail.

Mile Oak Image 1 LHS
Mile Oak Image 2 LHS
Mile Oak Image 1 RHS

The Solution

Following award of the temporary works for the ASP, the MGF digital team prepared a short animation, which detailed the installation sequence in a 3D output. The intention of this was a digital rehearsal to share information with the delivery team for possible improvements, it was also available to use during toolbox talks to understand key stages.

For the ASP, the optimised temporary works design included a multi frame (two level) sheet piled solution that was 40.5m long x 15.2m wide x 6.5m deep. This included the use of GU16N piles in combination with the MGF 406UC, 400 series cross struts and knee braces (lower frame only). The temporary works equipment allowed the permanent ASP structure to be built internally and back filled around the outside.

Working in collaboration with the Principal Geotechnical Engineer from MMB, four analyses were carried out and independently checked. This included total and effective stress analysis at the North and South of the cofferdam.

During an initial meeting, groundwater levels were agreed upon, based on current plus historic data and the time of the year the excavation was planned to take place.

An allowance was also made to over excavate the South end of the cofferdam to remove a band of silt that was expected, based on the ground models.

To assist with the installation and prevent incorrect build up on site, MGF marked each piece of the frame with a specific number which was linked to the construction drawing.

Mile Oak Image 1 LHS ROW 2
Mile Oak Image 2 LHS ROW 2
Mile Oak Image 1 RHS ROW 2

The Verdict

The collaboration and engagement guaranteed the use of a two-frame solution instead of a potential three, resulting in a cost saving of approximately £4000 per week. Wider savings of this solution included the time to install the third frame and the impact that would have on the construction programme.

Environmentally, the removal of the third frame prevented approximately 476kg CO2e being released into the atmosphere, based on 3 articulated lorry deliveries (6 journeys at 9MPG).

MGF were invited to three JN Bentley seminars across the country to celebrate fifty years of project delivery, where we demonstrated best practice, highlighted the Mile Oak project and were happy to affirm our continued relationship with MMB.

For more on this case study see the video below: