Pump up the volume

Abstract

Ten intense days of jet grouting inside a Victorian pump station in Reading have accomplished the risky business of lowering the building's floor level through waterlogged soil. Bachy Soletanche has completed 67 jet grouted columns which form the rectangular cofferdam and its 1.2m thick base that surround and underlie the station's concrete floor slab. This has created a dry environment for contractor John Murphy and Sons to break out the old slab, excavate the ground beneath and build a new floor 1.4m lower. The challenge was to form a temporary works cofferdam through the waterbearing ground and inside the congested building with limited headroom. Options such as dewatering, ground freezing or secant piling risked either heave or settlement damage to the listed structure, or a less than 100% water seal. An even greater concern was ensuring the safety of a bank of live pumps only metres away, through which much of Reading town centre's combined sewage and drainage flow has to pass uninterrupted.