Abstract
A deep vertical shaft down to 50m and a relatively large-diameter tunnel were excavated in a sedimentary mudstone deposit for research purposes. The deformation characteristics of sedimentary soft rock was studied from field observations and their back-analysis taking into account the initial stress state estimated by the over-coring method. The Young's modulus from the field behavior was very similar to that obtained by various in-situ tests and the triaxial tests when the strain level-dependency of stiffness and shear stress-dependency of that evaluated by the triaxial compression tests are considered. Therefore, in this mudstone deposit, the effects of cracks, joints, faults and the confining pressure are insignificant.
