ABSTRACT
In the design of tunnels, both mechanical parameters and initial stresses of rock masses are important input data. Another important aspect of back analyses for assessing the stability of tunnels during the excavations is to achieve the prompt feedback of back analysis results to the way of excavation procedures, and to verify the adequacy of support measures without any delay. This chapter describes the mathematical formulation of the back analysis procedure based on the flexibility matrix methods proposed by Sakurai & Shinji, in which the normalised initial stress is used, so that the initial stress of the ground around the tunnels is not needed. Back analyses were carried out for determining strain distributions around the tunnel from measured displacements. In order to assess the stability of tunnels, the maximum shear strains occurring around the tunnels are compared with the critical shear strain of the geomaterials.
