The geology and geotechnical properties of the Thanet Sand Formation – an update from the Crossrail Project

Crossrail is one of the most significant infrastructure projects undertaken in the UK with a projected usage of 200 million journeys/ year. It will provide a high capacity train service operating at a peak frequency of 24 trains per hour and bringing an extra 1.5 million people within 45 minutes of central London. The central underground section is tunnelled to pass beneath the built up city and to avoid existing infrastructure such as piles and metro tunnels (Figs 1 & 2). Tunnelling and station excavations of up to 40m depth have been necessary, deeper than previous infrastructure works in London. As a result of the increased depth and extensive lateral extent, the Crossrail works encounter or are influenced by the Thanet Sand (TS) Formation over a wide area, from shallow exposures in the east, where its base is at a depth of 18m or less, to deep conditions in the west where its base is 40m deep or more (Fig. 1).