Using BGS models and technology to facilitate tunnel construction – an example from Farringdon, Crossrail.

GSI3D is a geological modelling software package and methodology developed by BGS in collaboration with INSIGHT GmbH. A detailed geological model was constructed using this software for the Farringdon area of London (Aldiss et al 2012 http://nora.nerc.ac.uk/20346/). The software and geological model is being used by consultants (the Dr Sauer Group) who are excavating the tunnels which will form Farringdon Crossrail Station. The modelling methodology allows Dr Sauer to update the geological model in real-time as new information and data about the subsurface is obtained from the excavation. This helps the geologists working at Farringdon Station to plan and monitor the excavation process. The main purpose of the modelling is to anticipate faults and sand lenses which might be saturated with water causing a potential hazard to the machines and staff. BGS geologists have been consulted during excavation work to provide expert input to the modelling and conceptualisation of the geology. This is the first time a BGS geological model has been used and iterated directly during a construction project. Reports from Dr Sauer suggest that it has the potential to significantly reduce risks and cost and is likely to have high impact in the industry. Angelos Gakis (Chief Geotechnical Engineer for Dr Sauer Group) has documented the use of the model and methodology (Gakis et al 2014 (in press) Geotechnical Risk Management for Sprayed Concrete Lining Tunnels in Farringdon Crossrail Station, In: Proceedings of the World Tunnel Congress 2014 – Tunnels for a better Life. Foz do Iguacu, Brazil) and the following is a summary written by Mr Gakis: “The main purpose of the 3D model is to give an improved spatial understanding of the expected ground conditions concurrently with the construction progress, which in case of Farringdon Station is quite complex. Data from the face mapping has been progressively integrated into the model on a daily basis, thus providing a visual geological database for predictions of constantly increasing accuracy for future tunnels. After the excavation of each tunnel section the data from the face mapping was integrated in the 3D model. Thus, the risk was reduced as the level of knowledge and confidence was constantly increasing. At the same time in-tunnel probing provided additional data, validating at the same time the prediction from the 3D geological model”