The observational technique of compensation grouting was adopted as a flexible solution to safeguard the viaduct against adverse settlements. GCG was engaged to provide specialist technical support to the Asset Owner and Designer. Our role included preliminary, detailed and construction stage design of compensation grouting works, site support during construction and close-out reporting.

For the first such application, curved tube à manchettes (TAMs), installed by directional drilling were used to provide access for controlled grout injection. Grouting was at a level between the tunnel and the viaduct foundations. The controlled grouting induced heave was used to reversed the tunnelling generated settlements, as they occurred. The net result was that the viaduct only experienced small and acceptable settlements and distortions. Real time monitoring allowed proper management of the grouting and tunnelling activities.

Preparatory works included a field trial and two pre-tunnelling grouting stages in which 714 m3 of grout was injected to fill existing voids and to tighten the ground. During the TBM passages, an additional 156 m3 was injected to control differential settlements within the design thresholds.

Publications:

Iannotta, F., Pigorini, A., Mair, R. J., Facibeni, L., Harris, D. I., Menkiti, C. O., Leoni, F. (2007) Applicazione della tecnica del compensation grouting per il controllo dei cedimenti indotti dallo scavo di gallerie al di sotto di un viadotto ferroviario. Proc. XXIII CNG – Padova, Abano Terme. (Application of the technique of compensation grouting for the control of sediments induced by excavation of tunnels beneath a railway viaduct, in Italian)