The design of tunnels and their subsequent construction can involve a high level of risk, especially with respect to unforeseen ground conditions or constructability issues. The management of such risks is essential and critical, and for the Tsuen Wan Drainage Tunnel (TWDT) was implemented by the inclusion of the Geotechnical Baseline Report (GBR) into Tender Documentation. The GBR included characterization of the geotechnical parameters and the geological conditions, in such a manner so as to allow the definition of an appropriate construction methodology, and optimal excavation and support techniques. This paper describes how the ground condition risk was managed on this Project utilising a custom-built Double Shield Tunnel Boring Machine (TBM), highlighting the use of detailed geotechnical characterisation as the primary driver for offsetting risk from unforeseen or changing ground conditions during tunnelling.