Compensation grouting to limit settlements during tunnelling at Waterloo Station, London

A new escalator tunnel and associated passageways have been constructed at Waterloo Station in London. The tunnels pass through Thames Gravels and London Clay only a few metres beneath two important masonry structures: the Victory Arch and the Waterloo and City Line railway tunnels. In the absence of protective measures, the settlements of these structures would have been large and would have caused significant damage. Compensation grouting was therefore undertaken in the ground between the tunnels and the overlying structures to limit settlements to acceptably small levels. An essential feature of the technique is the carefully controlled injection of grout during tunnelling in response to detailed observations of ground and structure movements. Settlements of the structures due to tunnelling were restricted to less than 15 mm. The relatively novel technique of compensation grouting has proved to be very successful in limiting settlements of structures during tunnel construction.