| Due to the complex characteristics of tunneling problems, tunneling engineering is perhaps one of the areas in which numerical methods are more frequently adopted in practice. One important application is to examine the influence of an excavation and construction procedures on the stress distribution and deformation in the ground surrounding the opening and on the tunnel lining. Another important aspect of tunneling problems that can be accounted for in a numerical analysis is the complex geometry associated with typical applications. This is not only related to the shape of the opening, but also to the presence of non-homogenous or non-isotropic soil strata.A constitutive model that is suitable for the analysis of structured clays has been developed in this study based on the multilaminate framework. The model takes into account the elastic unloading-reloading, inherent and induced anisotropy, destructuration and bonding effects. The model is implemented into Plaxis finite element program, successfully calibrated and used to investigate the response of structured sensitive clay to the construction of the Gatineau tunnel in Gatineau, Quebec and the Ottawa sewer tunnel in Ottawa, Ontario. Numerical results were compared to the field measurements taken during the tunnel construction. To improve the performance of the numerical model, an implicit integration algorithm is implemented and proven to be very effective as compared to the conventional explicit integration methods. The effect of different soil parameters including bonding and anisotropy on the tunneling induced displacements and lining stresses is also examined using a comprehensive parametric study. The results indicated that soil bonding and anisotropy have significant effects on the shape of the settlement trough as well as the magnitudes of surface displacements and lining stresses induced by tunneling. |
