Page 200 - Numerical Analysis and Modelling in Geomechanics

BACK ANALYSIS OF GEOTECHNICAL PROBLEMS 181

Figure 6.4 Surface settlements recorded during the tunnel excavation.
These results suggested some possible changes to the construction technique,
to limit the settlements during the second stage of excavation. They should
increase the bearing capacity of the foundations of the crown arch, for instance,
by introducing additional sub-vertical jet grouted columns at the liner shoulders.
Since this modified technique involves relevant technical problems, and an
increase of the cost of excavation, it was decided to carry out a preliminary
evaluation of its effectiveness by means of a finite element simulation. It was