Multi-aquifer pressure relief in east London

摘要

Two adjacent deep shafts in east London involved excavation to 30 m below standing groundwater level and required temporary control of pressures in the Lower Aquifer below the London Clay. Three distinct aquifer horizons were present comprising the Lambeth Group channel sands, Thanet Sand and Chalk. One of the shafts was constructed using a circular diaphragm wall with a reinforced concrete base slab and the second shaft was constructed using SCL techniques with a domed base. The different structural approaches plus slightly differing depths led to radically differing requirements for groundwater control which are explored in this paper. One of the shafts required substantial lower aquifer pressure relief which was achieved using deepwells targeting the Chalk plus a combination of external pumped Thanet Sand wells and internal passive wells separately targeting the Thanet Sand and Lambeth Group. The second shallower shaft was successfully constructed using internal passive relief wells.