Application of numerical simulation at the tunnel site

Abstract

Since the tunnel engineer often has to respond quickly to unexpected ground conditions, rapid results from numerical simulations performed on site could serve as a tool, which assists important decisions. One object of the project was to evaluate the efficiency and applicability of 2D and 3D finite element methods (FEM) and boundary element methods (BEM) to simulate tunnel advance under different geotechnical conditions. Another task to be performed during this project was to make site data available to other projects within the JRI.

The finite element and boundary element code BEFE was used ([1]). The simulations were occasionally performed on site in order to gain experience with the practical applicability and efficiency of the numerical tools. Modelling techniques for excavation sequence and support were investigated, as well as the model influences on the results. The modelling approach was evaluated using criterion such as the time spent for model set-up, calculation and processing the results. Improvements in methods of data evaluation of results for a direct comparison with monitored data are presented. The calculation time and disk storage requirement using a Conjugate Gradient Solver (CG) are compared to a Frontal Solver for different model sizes. The development of longitudinal displacements and the orientation of displacement vectors are presented for homogenous and heterogeneous ground conditions. The influence of different primary stress conditions on the displacement pattern was investigated as well. Finally, the practical application of the numerical models is demonstrated by case histories.