Evaluation of hypoplastic model for soft clays by modelling of Nicoll highway case history

摘要

The paper presents evaluation of the newly proposed hypoplastic model for soft clays by modelling of the welldocumented geotechnical failure of a deep excavation of Nicoll Highway, Singapore, in 2004. The marine clays present at the site are typical normally consolidated soft clays, exhibiting large deformability and stiffness and strength anisotropy. These features - anisotropy of asymptotic state boundary surface and the effect of normal consolidation on stress paths and stiffness anisotropy - have been included into the newly proposed hypoplastic model. In the paper, it is first demonstrated that the model predictions compare well with experimental data from element tests on Singapore clay and improve predictions over original hypoplastic model. Secondly, numerical simulations of Nicoll highway excavation focusing on specific cross-section within the collapse area are presented, showing good fit between inclinometer data and simulations up to the final stages immediately preceding the excavation collapse. The simulation results are compared for previous version of the hypoplastic model, along with Mohr-Coulomb model with effective and total stress parameters. Subsequently, the influence of the model parameters on simulation results is studied and it is shown that the parameters affecting extension strength are more significant than parameters affecting pre-failure non-linearity.