Twin-tunnelling: Case studies in clay

New developments in the theory and practice of tunnel construction are essential for the industry to progress but it is the relationship between these two areas that is equally as important. Tunnelling practice has greatly benefited from laboratory research; specifically, centrifuge modelling linked with field measurements. The wide body of work on the construction of single tunnels has led to the identification of parameters and techniques that are widely accepted for predicting and assessing the magnitude and extent of tunnelling ground movements. However, the usage of twin tunnels in urban areas for transportation purposes have increased and better understanding on the associated ground displacements are required. This paper firstly provides background to ground displacements due to single tunnel, twin tunnel constructions and common prediction methods used in practice. Then, it introduces recent technological advancements in centrifuge modelling, applied to the complex geotechnical events of twin-tunnelling, that has led to further insight. The tunnelling induced ground displacements obtained from twenty four case studies in clay around the world and eighteen centrifuge tests are presented for further analyses. From that, a comparison between the recent theories of proximity-dependent tunnelling-induced ground movements with case histories has been carried out to establish their validity and limitations. Published field measurements have been reanalysed taking into account newly discovered relationships between the tunnels’ proximity and the magnitude and extent of ground movements, reflected via volume loss and the settlement trough width, respectively. The applicability to field measurements of the additional volume loss prediction method (derived from consideration of the experiment work) for tunnelling in clay is assessed.