ABSTRACT
It is of interest that the critical strain is continuously distributed from soils to hard rock. In order to determine the reduction coefficients, intact rock specimens were drilled from rock masses at the place where both the plate bearing tests and the direct shear tests had been conducted. The intact rock specimens were tested in the laboratory to determine Young's modulus and the uniaxial compressive strength. An approach for assessing the stability of tunnels should be simple enough to be easily applied for tunnelling practice at construction sites. In tunnel construction sites, it is extremely important to assess the stability of tunnels immediately after taking the data of measured displacements. In the design analysis of tunnels, the mechanical parameters such as Young's modulus and strength parameters (cohesion and internal friction angle) of rock masses are important input data, which can be determined by plate bearing tests and direct shear tests.
