SUMMARYThis paper describes the development of a numerical model for compensation grouting which is a useful technique for the protection of surface structures from the potentially damaging movements arising from tunnel construction. Pipes are inserted into the ground between the tunnel and the overlaying structure from an access shaft. Buildings on the surface are instrumented and movements are carefully monitored. Once the deformations exceed a certain Trigger Level, grout is injected into the ground to prevent damage. In the finite element model described here, compensation grouting is modelled by applying an internal pressure to zero-thickness interface elements embedded in the mesh. An 'observational algorithm' is used, where the deformations of the surface are monitored and used to control the injection process. Example analyses of compensation grouting are given for three-dimensional tunnel construction underneath a greenfield site. Different strategies are used to control the injection process and their effectiveness in preventing surface movement is assessed. The numerical model is shown to replicate general behaviour expected in the field and is capable of modelling the control of ground surface movements at a greenfield site.

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