Thames Tideway Tunnel: TBM performance in the London Clay Formation and overcoming man-made obstructions

An earth pressure balance tunnel boring machine (TBM) was used to construct the 6.5 m internal diameter, 7 km long, section of the Thames Tideway Tunnel project’s main tunnel between Fulham and Acton, in west London. The tunnel was excavated entirely within the London Clay Formation (LCF) containing several divisions (B, A3 and A2). Recognition of these within the ground investigation and later, during shaft construction, provided valuable assistance in the production of an accurate ground model, which further led to the identification of several geological faults. The TBM did not encounter any adverse ground conditions and its performance was seemingly not affected by the different LCF divisions or the faults. However, it was significantly impacted by intersecting two existing boreholes, resulting in the activation of contingency procedures. These included skilfully changing the TBM operating parameters, in addition to increases in the frequency of and additional in-tunnel and surface settlement monitoring to safeguard the integrity of the tunnel structure and surrounding groundmass.