Severn Trent Water Strongford

Overview

The Severn Trent Water scheme provides a replacement system for the storage and return of 19,755m3 of storm sewage at its Strongford facility located by the River Trent at Barlaston, Stoke-on-Trent. DAWSON-WAM provided the design, supply and installation of 4nr, 11.5m diameter, 7m deep sheet piled cofferdams to enable below ground construction works of the central hoppers and the Storm Return Pumping Station for the scheme.

Technical information

• Contract comprised installation of four sheet piled cofferdams for the storm tank hopper construction and a sheet piled cofferdam for an Inlet Pumping Station
• Hopper Cofferdam diameters - 11.5m
• Depths - 7m approx.
• Inlet Pumping Station Cofferdam diameter - 18m
• Depth - 10m approx.
• Gound conditions were very poor as the site is located on the flood plain of the Rive Trent, adjacent to the river.
• Ground consisted of soft clay overlying water bearing sands and gravels before encountering sandstone rock and/or clay
• Sheet piles lengths used for the Pumping Station Cofferdams were 16m
• Sheet pile lengths for the Hopper Cofferdams varied between 12m and 16m
• All piles were installed using DAWSON-WAM's TM18/22B ABI Leader RIg fitted with vibro hammer
• Some piles in the Pumping Station were impact driven to the rock
• The Pumping Station Cofferdam was designed with three levels of framing/ propping
• Black & Veatch installed dewatering to all cofferdams
• Cofferdams were designed to withstand the ground pressures in event of dewatering failure
• Two of the Hopper Cofferdams were installed with an external reinforced concrete ring beam for the the propping system, the remainder installed with an external and internal ring beam
• Process and outline design for the entire scheme was undertaken by Grontmij.