1. How to simulate the digging of a tunnel?

1.1. Principle of the method, implementation and validation

Background

Geomechanical studies are generally based on a simulation of underground gallery digging. Examples of applications can be cited:

1. assess the area damaged by the excavation (EDZ) around a storage gallery;

2. study the restoration of a storage cell by site waters.

A number of studies have already been conducted by department AMA on this subject, with*Code_Aster*. However, few practical elements are available in the documentation to reproduce this type of calculation. Department MMC has undertaken such modeling with Code_Aster, in order to appropriate the procedure for applying the method traditionally used for this type of calculation: the « convergence—confinement » method. It appears from this experience that this application is not a completely trivial step that it is necessary to ask some practical technical implementation questions. Capitalizing on this experience for future users appeared to be quite important, in the collective interest of studies on storage in particular.

Goal

The main purpose of this note is to provide some preliminary technical advice to Code_Aster users who want to model an underground excavation.

Methodology

This note presents an application to a Code_Aster command file of the convergence — confinement method. After a brief reminder of the principle of the method, a practical and operational description of the commands to be used is given. The method is illustrated by validation calculations of*Code_Aster*, whose command files are provided in the appendix.

Result

Thanks to the implementation of the proposed protocol, two*Code_Aster* validation calculations were implemented. The relative difference between numerical results and analytical solutions is less than 2%.

Perspectives

The method can be extended to non-linear calculations (plasticity, damage) and coupled in THM, in particular in the context of studies intended for the storage of nuclear waste.