BTS April lecture focuses on Kilsby Tunnel groundwater

Mike Chrimes, vice-chair of the ICE panel for historical engineering works, and Martin Preene, technical director, Coffey Geotechnics Ltd, will discuss groundwater lowering for construction of the Kilsby Tunnel on the London to Birmingham railway

The Kilsby Tunnel, constructed in the 1830s under the direction of Robert Stephenson, faced severe problems when a section of the tunnel, almost 400m long, was driven through water-bearing unstable ‘quicksand’.

Contemporary methods were not well suited to tunnelling through such conditions. In previous decades, several canal tunnels had been planned to specifically divert around expected ‘bad ground’, and others took years to complete at great expense.

Drawing on their experience from the mining industry, Stephenson’s team, worked through the unstable ground, although with considerable delays and cost increases.

Their success was achieved, in part, by establishing a large-scale groundwater pumping system, unique for the time, that lowered groundwater levels and stabilised the quicksand, which resulted from a buried channel of glaciofluvial sands, cut into bedrock, that had been missed by trial borings. Steam engines were used to pump from multiple shafts – including four dedicated pumping shafts, offset from the tunnel alignment – with a reported pumping rate of 136 litres per second for several months.

The work at Kilsby was two decades before Darcy’s law established the theoretical understanding for groundwater flow. Despite the lack of existing theories, Stephenson used careful observations and interpretation of groundwater flow in the ‘quicksand’ to navigate the tunnel project to a successful conclusion.

The lecture – a joint event with the British Geotechnical Association and the Engineering Group of the Geological Society – will be held on April 18 at the ICE in George St, London W1P 3AA. It is an in-person meeting, which will also be streamed live at https://www.youtube.com/watch?v=T7TfKfEb93s

At this month’s meeting, on March 21, the three finalists for this year’s Harding Prize will present their papers.