Mersey Gateway Bridge

Project Overview

Temporary dewatering of Sherwood Sandstone required for 3no x 40m Ø cofferdams for the construction of bridge pylon foundations within the River Mersey for new bridge spanning Runcorn and Widnes. Dewatering was also used to dewater bridge pier cofferdams crossing the Manchester Ship Canal.

Mersey Bridge Piers

Using site investigation data a design was established to dewatering the Sherwood Sandstone and overlaying granular Alluvium material to below excavation level. 6no x 32m deep pumping wells were installed around the internal perimeter of each bridge pier cofferdam. Passive pressure relief wells where installed within the central section together with an array of VW monitoring piezometers. Pumping tests during the commissioning stage confirmed the dewatering design and effectiveness.

Manchester Ship Canal Bridge Piers

Conceptual dewatering models were developed with subsequent undertaking of a pumping test to establish flow, connection with the canal itself and groundwater quality. Further to this an array of internal dewatering wells were located within the sheet pile cofferdam. Dewatering was achieved using a deep well pumping system with continual monitoring of discharge flow and water quality.