Deephams Sewage Treatment Works (STW)

Deephams Sewage Treatment Works (STW) is one of the largest waste water treatment plants in the UK and was upgraded between 2013 and 2019 to accommodate a 989,000 population equivalent. The aim of the project was to improve the quality of effluent released into the River Lee, to comply with more stringent Environmental Agency standards, and to reduce odour levels by 90%. We also needed to increase the capacity of the site, to facilitate a future population rise. The new pumping station required a shaft of internal diameter of 18.5m and an invert depth of 21m to provide operational freeboard to the invert of a low-level sewer, 15m below ground level. To account for the overall permanent design, including a 600mm thick in-situ concrete lining and a 3.5m deep base plug, the temporary shaft required a 24m deep excavation.

Ayesa was appointed by Murphy to develop a solution utilising secant pile techniques. Originally diaphragm walling was specified due to the depth of the shaft. The final design challenged traditional techniques as it pushed the limits of acceptable secant pile depths in the UK.

The project was the winning entry in the Concrete Society Awards Civil Engineering category where Ayesa’s contribution was recognised for our innovative use of the permanent lining as temporary ring beams whilst maintaining a high-quality finish, in addition to the innovations incorporated into the secant pile design.