Abstract
In order to assess the stability of tunnels, Sakurai proposed a method called Direct Strain Evaluation Technique (DSET). According to this method, strain occurring in rocks around tunnels is compared with its allowable value, and if the occurring strain is still smaller than the allowable value, tunnels are deemed stable. Considering that the failure of materials can be evaluated in terms of the maximum shear strain, this study defined critical shear strain as an allowable value for the maximum shear strain. The critical shear strain must be determined by a torsional shear test. However the test is often too complex and time consuming to operate. In this paper, there fore, it is demonstrated that the critical shear strain can be determined from uni-axial or tri-axial compression tests which are commonly used in engineering practice.
