Prior to constructing the two new rail tunnels, 1,208 metres in length with a diameter of 6.4 metres, it was first necessary to dismantle 150 metres of existing tunnel. The machine used was a first of its kind: the Tunnel Dismantling Machine (TDM), an innovative TBM that reversed the construction process. The TDM maintained a confinement pressure of three bars to enable dismantling of the existing segments and back-filling of the tunnel, in soft soil located below the water table in Hong Kong’s city centre. The main advantage of this unique procedure was that it limited challenging dives in hyperbaric conditions by mechanising the process.