Geological modelling, the observational method and management of ground hazards: Ramsgate Harbour Approach Road Tunnel

The Ramsgate Harbour Approach Road Tunnel (RHART) was the first to use the prevaulting tunnelling method in the UK. As with other forms of open-face tunnelling, this method relies on the establishment of a reliable pre-construction geological model and continual verification of this model during construction by use of the observational method. The route was thought to pass through difficult ground conditions containing a number of natural and artificial hazards which, if not managed properly, would have serious implications for health and safety during construction. This paper illustrates how geological modelling was used for early identification and prediction of such hazards, enabling the planning of contingency procedures. By incorporating the observational method in the construction process the site team was able to assess the accuracy of predictions made from the ground model. Procedures adopted during construction of the Ramsgate Harbour Approach Road Tunnel illustrate how results from continuous in-tunnel and surface observation and monitoring lead to increased confidence in the geological model and the prediction of ground behaviour. Adoption of these procedures reduced the risks posed from unforeseen ground hazards and significantly improved health and safety issues for personnel during construction.