The Application Of Element Embedded Discontinuity Model To The Failure Process In Structures

Strain localization is closely related to the material instability and an important characteristic of failure of structure. From the perspective of mathematic model, the type of governing equations will be changed when this phenomena occurs. If the standard FEM is used to deal with this problem, because the energy dissipation can't be considered properly, the result related to localization deformation will vary with the mesh size and mesh alignment. The Strong Discontinuity Analysis has the capabilities of determining the appearance and the evolution of discontinuity solution and the reasonable energy dissipation mechanism which is consistent with the strain softening law of material. The elemental embedded discontinuity model, which is based on this method and the Assumed Enhanced Strain method, can capture the weak and strong discontinuity in the element and track their evolution process without remeshing. In this thesis, this model is employed to study the failure process for geotechnical engineering and concrete samples. The main works related to the thesis are described as follows.(1) According to the algorithm proposed by Borja R. et al., the FEM code is implemented. This algorithm is based on the Assumed Enhanced Strain method, in which an appropriate incompatible mode containing an approximation to the displacement jump is added to the underlying standard element.(2) For the Geo-material with softening branch which obeys the Drucker-Prager criteria and non-associated flow rule, the classical problems in soil mechanic under plane strain condition are simulated by the element embedded discontinuity model as follows:(a) the evolution process of shear band in rectangular specimens; (b) the progressive failure process in homogeneous and inhomogeneous slope; (c) the failure process and the ultimate bearing capacity of the foundation subject to eccentric loads; (d) the whole failure process of backfill passively pressurized by the retaining wall.(3) The process of tensile failure in concrete specimens is studied under plane stress condition for the Rankine elastic-plastic material with softening branch.The numerical results show that the progressive failure phenomena occurring in geotechnical engineering structures and concrete specimens can be numerically simulated effectively by the element embedded discontinuity model. Because Strong Discontinuity Analysis provide the regularization for the ill-posed governing equation, it is able to capture the strong discontinuity and can greatly reduce the mesh dependence of the solution which is common when the strain localization problem is solved by standard FEM. Meanwhile, the post-localization path can be traced partly. The results also indicate that this model can be taken as a beneficial supplement to traditional limit equilibrium method in stability analysis of slope and foundation. It can also provide technical basis for the study of failure mechanism and reinforcement of the geotechnical structures.