Ground Investigation work for the High Speed 2 rail route in west London has unearthed what is believed to be a previously unknown geological horizon at 33m below ground level.
Workers in Ruislip have logged a black clay layer, which HS2 has named the Ruislip Bed, which is thought to have been formed from densely wooded marshes on the edge of a sub-tropical sea.
The unexpected clay layer was discovered investigating ground conditions in the area, prior to the construction of the 14km long Northolt Tunnel, which will run from West Ruislip to Old Oak Common.
“Although ground investigations regularly take place across the country, it’s really exciting and very unusual to come across a material that no-one has ever seen before,” said GCG senior partner Jackie Skipper. “The ‘Ruislip Bed’ discovery is particularly fascinating, as it is a window into our geological history.
“It would have been formed during the Paleocene period, which was a time of intense change, with new animals evolving following the extinction of the dinosaurs. Most of Southern England was covered by a warm sea and this clay helps us to pinpoint where the coastline was.”
HS2 has confirmed that the ground investigation programme on phase one of HS2 will be largely completed by the end of this month but will be followed by a series of supplementary investigations to target specific areas. This additional ground investigation work will be undertaken by HS2’s framework contractors.
HS2 ground investigation programme manager Steve Reynolds said: “Our main investigations are almost complete, with over 1 million laboratory tests undertaken on the samples we have taken. It’s the largest ground investigation programme that the UK has ever seen and an unparalleled opportunity to learn about the ground beneath our feet.”