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Author |
|
| Name |
Callari, Carlo
carlo.callari@unimol.it |
| Research field | Computational Geomechanichs, Computational Poromechanichs |
| Career stage | professor |
| Home university/institution | University of Molise |
| Department/Research unit at home university/institution | DiBT Department |
| Chair/Working group at home institution | Engineering Division |
International activity |
|
| Country | Germany |
| Location | Bochum |
| University | Ruhr-Universität Bochum (RUB) |
| Fund Research School | VIP |
| Type of activity | research stay |
| Period |
starts 15-12-2014 ends 15-12-2015 |
| Keywords | Strain localization; Tracking algorithm; Strong discontinuities; Enhanced assumed strain; Finite element method; Shear band |
| Report |
The project activities are focused on the development of a new 3D strategy for discontinuity tracking in the framework of finite element analysis of shear failure zones in soils and rocks with embedded strong discontinuities. The goal is to enable a high resolution of computational simulations of shear failure zones in soft soils. Such localized failure zones may lead to the sudden appearance of sinkholes, landslides or tunnel collapse, in particular in the presence of groundwater. It should be emphasized, that this joint research has a particular significance for the Ruhr-Area, as sinkholes (“Tagbrüche”) often occur in this region. As a matter of fact, the tracking of displacement discontinuities is known to play a crucial role in a successful numerical analysis of localization zones such as shear failure bands. Available algorithms are typically based on the so-called “propagation” strategies and have proven to be effective for discontinuity tracking in 2D problems. In these algorithms, the discontinuity is progressively activated at the local level by means of element-wise segments, preserving its continuity across the common boundaries of traced finite elements. However, the extension of these algorithms to 3D problems is often difficult , motivating approaches based on the level set method or strategies involving the solution of a global elliptic problem. In the present project, we are developing an alternative advantageous novel strategy for global tracking of the discontinuity surface. It is based on exploiting information obtained from the so-called "incompatible modes" employed in a special finite element technology denoted as Assumed Enhanced Strain formulations (AES-FEM). The enhanced-strain methods are able to capture localized shear deformations definitely better than standard finite elements (see the figure above). This result can be explained as a consequence of the improved performance in bending. We observed that the approximation of the strain jumps delimiting the shear band is connected with a deformation field characterized by opposite bending curvatures across these two discontinuities. Thus we have formulated and verified a new scalar function of the enhanced modes to locate the surface of the potential shear failure zone. Among the advantages of the strategy developed in this project, we remark its global character, which allows for the evaluation of discontinuity surfaces that are continuous by construction through the elements, with a negligible computational cost. However, still a number of problems observed in selected applications have to be solved. These problems will be tackled within the upcoming visits of Prof. Callari at RUB. |