Numerical analysis of Double-O-Tube shield tunnelling

Abstract

Underground tunnels play an important role in the mass transportation systems in modern cities. The ground movements induced by tunnel excavation in short term and long term are of great concern due to their potentially irrecoverable impact on the surrounding buildings and services. The numerical modelling, in conjunction with well documented case studies to validate the modelling approach, is an efficient methodology for adequate and robust predictions of the ground response caused by tunnelling. The Double-O-Tube (DOT) shield tunnelling is a new technology developed since 1989, and has been applied in over 20 engineering cases in China and Japan. Due to its unique double tube cross-sectional shape, the DOT tunnel is expected to perform differently in mechanical terms compared to traditional twin tunnels. Therefore, a systematic study of its engineering behaviour, of the ground response and of tunnel lining is necessary. This research involves numerical simulations and investigation of DOT construction in soft clay and stiff clay conditions, represented by Shanghai clay and London clay respectively, using Imperial College Finite Element Program (ICFEP). In the first part of the thesis, the Shanghai clay and the whole ground profile are characterised referring to the laboratory data and field experimental evidence. A numerical model is developed in ICFEP for the case of DOT tunnel in the Shanghai Metro system, applying an extended Modified Cam Clay (MCC) model to represent the ground conditions and discretising the tunnel lining with elastic beam elements. The predicted short-term settlement troughs achieve good agreement with the field monitoring data, validating the reliability of the numerical model. Additional sensitivity studies investigate the conditions of the tunnel lining joints and the effects of the pressure exerted by grouting in the constructions process. The second part of the thesis focuses on the modelling of the reinforced concrete segments of tunnel lining using an advanced elasto-plastic concrete model. The model validation is performed with the simulation of loading tests on a single lining segment performed in the laboratory, demonstrating very close agreement between the predicted and measured segment deflections under applied load and an accurate onset of cracking in concrete. Such a concrete model is applied in the analysss of DOT tunnelling in Shanghai to investigate its merits against a simpler lining representation. Finally, the application of DOT tunnelling is explored in stiff clay ground conditions, utilising the Jubilee Line Extension and the Crossrail case studies in London clay, and applying an advanced kinematic surface hardening model for soil behaviour. The comparison of numerical predictions against field monitoring data demonstrates comparable magnitudes of ground movements mobilised by DOT tunnelling with respect to conventional twin tunnelling.Open Acces