International Safety Awards 2017
Client: United Utilities
Project: Preston Tunnel, Lancashire, UK
Project partners: KIER Construction Ltd, J Murphy & Sons, Interserve Project Services, Integrated Alliance, KMI Joint Ventures, United Utilities
Located on the River Ribble’s north bank, the city of Preston is served by a combined sewer system installed in the 1870s. As the population grew, numerous reliefs were added to the small-bore pipes in order to drain excess flows into Ribble tributaries and Savick Brook. Inevitably, the city’s growing population and industry placed rising demands on this archaic system.
In 2005 the Environment Agency (EA) issued consents requiring a maximum of three spills per summer (Bathing Water Directive) and 10 spills per annum (Shellfish Waters Directive). All storm spills to the River Ribble were to be screened to 6mm in two dimensions.
Faced with seven unsatisfactory intermittent discharges (UIDs) from the existing sewer network, United Utilities needed to resolve these threats and provide the appropriate storage to satisfy the EA’s directives.
Longwood Engineering, United Utilities and its project partners worked closely together throughout the process. Longwood was commissioned to design, manufacture and install four huge Escalators capable of diverting Preston’s excess stormwater into a new 3.5km underground tunnel.
Produced at Longwood’s Yorkshire plant, the 12m long, 9 tonne Escalators are the largest ever manufactured. They comprise four Escalator screens and four off-conveyors (two horizontal and two inclined) which feed into two off-screenings compactor skips. The screw conveyors’ normal operating capacity is 5.5m3/hour.
The complex project also saw Longwood Engineering transporting the giant Escalators in sections and re-assembling them on-site. Longwood installed the Escalators at 60° angles with channel depths of 9000mm, a screen width of 2200mm and a flow capacity of 9000 ltrs/sec.
KMI Joint Ventures commented: “The installation and commissioning went very well. Post-installation snags were dealt with effectively, leading to a timely completion for both the screen installation and project as a whole. The screens have been in use for 14 months on intermittent storm duty without issue, which is a bonus for all concerned.”