Abstract
Large deformation and convergence have been commonly observed in tunneling through shale layers in the Shimanto Belt, in South Wakayama (Nanki) Region. They have caused serious damage to supporting members. The authors investigated the deterioration mechanism of the Tertiary Shimanto Shale (classified into several groups), appearing in tunneling, through the slaking test, polarizing microscopic observation and X-ray diffraction analyses in order to clarify the relationship between the deformation and geological characteristics. As a result, it was concluded that the deformation of shales was caused with the opening of the tectonically generated micro-fissure (aperture) by the reduction of confining pressure to rock which is associated with tunnel excavation. In addition, it was also found from the convergence measurement that the early installation of the invert lining was compulsory to control large deformation in tunneling.
