A study on determination of the relaxed zone around an excavated tunnel

When the amount of field measurement data is not enough to describe the whole behaviour of rocks around a tunnel, computer analysis can be used to complement that information. For basic procedure of numerical analysis using BEM, vertical displacements of the roof of large disc-shaped opening were analyzed. Analytical solutions for displacements around the disc-shaped opening were compared with numerical BEM solutions, especially the displacement discontinuity method. This paper presents an example which introduces the calculation method for the relaxed zone in rocks, with the above numerical analysis using data from field measurements. Taking into account the in-situ condition of rocks in the BEM analysis, an empirical failure criterion for rock was used. After determination of the relaxed zone by measurement at certain locations, it is shown that the calculated relaxed zone coincides with the above result. Accordingly, the complete relaxed area of rocks around a tunnel can be determined.