ABSTRACT
In order to assess the stability of underground openings, it is of primary importance to evaluate the extent of the plastic zone occurring around the openings. This chapter presents a back analysis method for determining the plastic zone appearing around underground openings. If the material constants and initial stress are back-calculated, the plastic zone can then be calculated by an ordinary elasto-plastic analysis. In the simulation, the displacements around an opening due to excavation are first calculated by an ordinary elasto-plastic finite element method, and they are used as virtual "measured displacements" in the computer simulation. The computer simulation has demonstrated that the back analysis method is highly accurate for determining the boundary between the elastic and plastic zones. The method requires only a linear elastic finite element analysis, so that it is possible to perform this back analysis at the construction site to monitor the plastic zone occurring around the openings.
