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

A new escalator tunnel and associated passageways have been constructed 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 grout during tunnelling in response to detailed observations of ground and structure movements. The observational method was used in the control of the compensation grouting operations. This was achieved by comparison of field observations with defined limits of acceptable behaviour, and by planned contingencies in the event that these limits were approached. The extensive instrumentation installed to monitor the movements of the ground and the structures during tunnelling is described. Details are given of the performance of the instrumentation, of the measurements made and of the interpretation of the observations required to evaluate the soil-structure interaction behaviour. The specified requirements for compensation grouting and a summary of the grouting operations are presented. Settlements of the structures due to tunnelling were restricted to less than 15 mm. The relatively novel technique of compensation grouting has proved very successful in limiting settlements.