ABSTRACT
This paper deals with the use of back analyses for interpreting the results of field measurements carried out during the excavation of rock structures such as tunnels and slopes. Field measurements are important to the rational design and construction of these structures. However, the measurement data are only numbers unless they are properly interpreted. Back analyses play a vital role in interpreting the measurement data properly. It should be noted that back analyses are not simply backward calculations. They must be developed on the basis of an entirely different concept in an analysis in which the mechanical modeling of the materials should not be assumed, but should be back calculated considering the results of field measurements. In this paper, an anisotropic parameter is introduced to simulate the non-linear behavior of geomaterials. By using this anisotropic parameter, a new constitutive equation is proposed, which is applicable to back analyses for interpreting the field measurement data. In addition, since the failure of structures cannot be predicted only through numerical analyses, the critical strain and the critical shear strain of geomaterials are proposed. They can be easily applied to assess the stability of tunnels and slopes. In slope engineering, the factor of safety is popularly used for assessing stability, while in tunneling practice the factor of safety is hardly ever used. This is because the factor of safety always becomes Fs = 1.0 if a plastic zone appears around the tunnels. To overcome this problem, hazard warning levels are proposed on the basis of the critical strain and the critical shear strain to assess the failure of tunnels. Some example problems are given to show just how to employ the hazard warning levels to assess the failure of tunnels.
