Designed and built an innovative overpumping solution, developed with our supply chain partners, to manage serious flows of up to 2,200 l/s.
The brick sewer tunnel at Whitlingham is 1.7m in diamter and over 11m deep, transferring foul sewage flow from over 280,000 customers in Norwich to the treatment works at Whitlingham. Proactive CCTV surveys of the sewer identified that the Victorian brick tunnel had incurred significant structural deterioration resulting from exposure to hydrogen sulfide. The damage had been exacerbated by a build up of over 100m³ of rag and debris within the tunnel, to a depth of nearly 1m.
Before any repair work could be started, an innovative over pumping solution was developed with our supply chain partners to manage flows of up to 2,200 l/s. The team could then focus on getting the sewer back to Grade 1 structural condition by pipe jacking GRP segments, preventing future damage from hydrogen sulphide exposure.
The project team wanted to get an accurate picture of the condition of the sewer, and opted for Sonar CCTV technology, providing a full laser scan profile of the tunnel, establishing that 360m of the asset required urgent rehabilitation. The construction team and supply chain worked closely to ensure substantial enabling works were completed early on in the project, allowing the team to safely undertake work on the collapsing tunnel.
The main challenge for the team however, was to complete the work with minimal disruption to customers’ supply. A cross section of the team came together to discuss options, and it was decided to construct a temporary offline wet-well to create a pumping station. This transferred flow back to the treatment works via 750m of 1m diameter above ground steel pipework, including two ‘pipe bridges’ over roads. This was installed and commissioned overnight during a short shutdown to prevent disruption and utilised a specialist pre-fabricated plastic section to control the flow out of the tunnel.
An 11m deep excavation was dug out over the existing tunnel. This provided access for the pipe jacking rig. Rescue teams and forced ventilation secured safe access for the miners working in the tunnel.
Facts and Figures
• This is the largest overpumping scheme in Anglian Water’s portfolio
• 360m of tunnel were repaired.
• £3.5 million cost in final business plan, with a forecasted outturn cost of £4.3 million
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