Investigation of tunnel movement of the Thameslink tunnels below site S3 of King’s cross zone development

Site S3 of the King’s Cross Development Zone is located in Central London to the North of King’s Cross Station. The site directly overlies the 11 m deep Thameslink twin-rail tunnels. The excavation of a rotary core borehole on site led to tunnel inward movement recorded by in-tunnel prism arrays. Live monitoring data has been used to investigate and determine the causal link between borehole RC1 and this movement. The borehole excavation lost excessive amounts of fluid flush into the London Clay. The interaction between flush fluid and soil is numerically investigated in this paper with an investigation into the numerical simulation of the physical excavation of the borehole itself. The aim of this research work is to investigate the mechanisms of movement that may have resulted in the tunnel deformation while numerical analysing the construction of the borehole in stages. Using a 2D plane strain model, the HSS (Hardening Soil with small strain) constitutive model has been utilised in order to recreate the stress history within the London Clay.