Ph.D Student | Elkayam Itai |
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Subject | Tunneling Induced Ground Displacements and Their Effects on Structures |

Department | Department of Civil and Environmental Engineering |

Supervisor | Professor Assaf Klar |

Full Thesis text |

The evaluation of tunneling effects on existing structure is an important process that engineers need to confront when dealing with the construction of new tunnels. Obtaining a solution for a general structure may pose a problem, as the solution involves significant soil structure interaction, and falls exactly in between the two disciplines of geotechnical and structural engineering. It is desirable to have a numerical method that allows simple communication between the engineers and still includes soil structure interaction, without the need for each of the engineers to explicitly consider the other system in his solution.

The main part of this thesis presents a framework in which the global soil structure interaction problem is divided between the two disciplines. One possible method for such decoupling is to extract condensed matrix of structure and the soil for a direct solution of the foundation displacements. The condensation method allows the structural and geotechnical engineers to individually build the condensed matrices without the help of the other. These two matrices can then be used for the direct solution of the problem. When an elastic solution is sought after, a single matrix can be composed based on stiffness method principles. While the assumption of elastic structure may be acceptable, the soil cannot be assumed to behave linearly. The research deals with this problem by representing the foundations as elasto-plastic entities with interaction between the different foundations.

The formulation is examined under different cases and evaluated by comparison with continuum based solutions. It is found that while foundation may be unloaded in the vertical direction they can still develop vertical plastic displacement, due to the nature of the plastic flow characteristic of the foundation. It is also found that due to the stress path dependency, correct representation of the advancing tunnel may be important if one wishes to obtain an accurate prediction of the strains within the structure.

This thesis also provides means of evaluating the effects of tunnel construction on nearby infrastructures (e.g. buried pipelines). In the thesis advanced analysis is performed using the Discrete Element Method (DEM) for the prediction of both greenfield settlements and their effects on pipelines. The formulation is first evaluated against centrifuge test results, and later used to evaluate linear equivalent methods for design purposes.