This presentation will cover dewatering strategies for underground infrastructure in the London Basin
Much of London’s early underground infrastructure was constructed through superficial soils, water bearing Terrace Gravels and London Clay. The dense over consolidated nature of the London Clay proved ideal for shaft sinking and open face tunnelling. Particularly over the last 40 years successive infrastructure projects have been constructed deeper, extending below the London Clay into the Lower Aquifer comprising Lambeth Group channel sands, Thanet Sand and the Chalk.
The Chalk has been exploited for water supply over the last 150 years resulting in a partially under-drained pore pressure profile in central London. Modern TBMs are capable of driving tunnels through water bearing ground but control of groundwater for launch chambers, ramps, shafts, caverns and connection tunnels remains challenging. This is particularly the case for urban construction sites with limited space and access. These constraints have spawned a range of strategies for investigating and controlling groundwater during construction, which exploit the differing hydro-geological characteristics of the Lower Aquifer strata, often involving a combination of partial cut-offs and pumping using both surface dewatering systems and in shaft/tunnel techniques.
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