Survey and analytical studies on a "TAKANUKE" collapse mechanism for greatly deeper shafts (Contract research)

Kurosaki, Yukio*; Yamachi, Hiroshi*; Matsui, Hiroya 

Mizunami underground research laboratory planned to excavate to 1000 m depth and now under construction. One of the most serious problems in a greatly deeper shaft is "TAKANUKE" collapse caused by slip movement of large discontinuities. In this report, we have conducted numerical studies using finite difference method in order to throw an objective light on a mechanism of TAKANUKE collapse. These studies show two different stress states in upper and lower side of large discontinuities. In order to evaluate a possibility of TAKANUKE collapse during MIZUNAMI main shaft sinking, we have conducted a particle body analysis as well. A fault with a high strike up to 79 degree, discovered in survey boring at MIZUNAMI site, has a low potential of TAKANUKE collapse during shaft sinking.