Assessment of plastic zone thickness and convergences for tunnels excavated in weak to fair quality rocks in Turkey

Satıcı, Özgür
Most of the ancient civilization structures were constructed under the ground, such as underground dwellings, transportation systems or storage facilities. In our modern era, underground constructions are still keeping their importance. Yet, every underground excavation requires prediction of rock mass behavior prior to excavation. Besides, this also means the prediction of convergences and plastic zone thicknesses after an excavation. In this thesis, development of convergences and plastic zone thickness during tunnel excavations were evaluated especially for weak to fair quality rock masses using actual field measurements, statistical and numerical analyses. Plastic zone thicknesses in relation with tunnel convergences were also identified. Decision tree method was selected as the best convergence estimation method, which is first in this kind and convenient for the determination of the relation between one dependent variable and multiple independent variables where there is not any linear relation within. As a result, a useful and user friendly convergence estimation model was generated. Moreover, the relation of convergences with plastic zone thickness was also revealed by the help of empirical equations, by using finite element analysis. Moreover, a new empirical equation was also identified for the prediction of tunnel wall closures. This equation is proved to be working well in the specified similar tunnel sections especially if three or more tunnel wall convergences are known and can be used for the estimation of unmeasured convergences for that section.