Advanced numerical analyses of EPB tunnelling using critical state plasticity

The paper discusses the effect of using several ground constitutive models on the numerical predictions of tunnelling induced ground movements. The numerical study utilizes an advanced 3D finite element model for EPB tunnelling, proposed by the authors, which allows realistic modelling of geometrical and operational complexities of EPB machines. Two constitutive models are used to describe ground behaviour, an elastic – plastic with Mohr – Coulomb failure surface and the Modified Cam-Clay (MCC) critical state plasticity model. For a fair comparison, the two models are calibrated to have similar compressibility and shear strength at stress levels corresponding to the tunnel axis. The results indicate that the MCC model leads to significantly higher crown displacements compared to the Mohr – Coulomb analyses, while ground surface settlement predictions are comparable. The observed behaviour is explained by the stress-dependent compressibility and more realistic non-linear stress-strain response of the MCC.