OBSERVATIONS OF GROUND AND STRUCTURE MOVEMENTS FOR COMPENSATION GROUTING DURING TUNNEL CONSTRUCTION AT WATERLOO STATION

A new escalator tunnel and associated passageways have been constructe d at Waterloo station in London, passing only a few metres beneath two sensitive masonry structures. Compensation grouting was undertaken in the ground between the tunnels and the overlying structures to limit settlements to acceptably small levels. This comprised injections of g rout during tunnelling in response to detailed observations of ground and structure movements. The observational method was used in the cont rol of the compensation grouting operations. This was achieved by comp arison of field observations with defined limits of acceptable behavio ur, and by planned contingencies in the event that these limits were a pproached. The extensive instrumentation installed to monitor the move ments of the ground and the structures during tunnelling is described. Details are given of the performance of the instrumentation, of the m easurements made and of the interpretation of the observations require d to evaluate the soil-structure interaction behaviour. The specified requirements for compensation grouting and a summary of the grouting o perations are presented. Settlements of the structures due to tunnelli ng were restricted to less than 15 mm. The relatively novel technique of compensation grouting has proved very successful in limiting settle ments.