This contribution presents a research on numerical simulation of strain localization due to shallow tunneling in soft ground. The attention is focused on the influence of hydro-mechanical coupling on induced displacements and collapse conditions. Hence, both the cases of excavation above and below the water table are considered, taking also into account the effects of partial saturation by means of a coupled finite element formulation for unsaturated poroplastic media. To capture localized failure phenomena in the form of dilatant sliding surfaces, the considered finite elements incorporate ad-hoc designed enhanced modes and algorithms for the integration of localized softening laws. For both the cases of full and variable saturation, the accumulation of fluid along these strong discontinuities is modeled by a discontinuous flow field. The appearance of localized solutions and their propagation path from the tunnel up to the ground surface is proven to be independent on the considered mesh and consistent with typical experimental data. These results are contrasted with solutions obtained by means of finite elements with no enhancement and standard continuum softening, showing the difficulties encountered by these conventional formulations in capturing strain localization.
Effects of Strain Localization on Tunnel Stability and Induced Subsidence
CALLARI, Carlo
2009-01-01
Abstract
This contribution presents a research on numerical simulation of strain localization due to shallow tunneling in soft ground. The attention is focused on the influence of hydro-mechanical coupling on induced displacements and collapse conditions. Hence, both the cases of excavation above and below the water table are considered, taking also into account the effects of partial saturation by means of a coupled finite element formulation for unsaturated poroplastic media. To capture localized failure phenomena in the form of dilatant sliding surfaces, the considered finite elements incorporate ad-hoc designed enhanced modes and algorithms for the integration of localized softening laws. For both the cases of full and variable saturation, the accumulation of fluid along these strong discontinuities is modeled by a discontinuous flow field. The appearance of localized solutions and their propagation path from the tunnel up to the ground surface is proven to be independent on the considered mesh and consistent with typical experimental data. These results are contrasted with solutions obtained by means of finite elements with no enhancement and standard continuum softening, showing the difficulties encountered by these conventional formulations in capturing strain localization.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
