Mechanized tunnelling by TBMs has been extensively adopted for last two decades. Nevertheless, only few case histories have been reported. Unlike NATM tunnels, the case histories of the weak zone have been seldom reported for the mechanized tunnelling, even in the other countries. In this study, a collapse of TBM tunnel occurred in the severely altered weak rock zones between volcaniclastic rocks and granitic rocks was briefly described. A systematic geotechnical investigation, which was performed to examine the cause of the collapse, was carried out at the site and then characteristics of the rocks in the zones were evaluated. Moreover, This study propose a guide line of estimateing the possibility of collapse in TBM tunnels through comparing experimental results with surveying results of general rocks.