Application of the multiple-layer supporting method to a tunnel in squeezing argillaceous rocks

摘要

Squeezing phenomena accompanied by the support failures have occurred at Konari work section of Iiyama Tunnel for Hokuriku Shinkansen (a bullet train line) in a Neogene mudstone formation where the overburden exceeded 180 m. To cope with this large squeezing earth pressure, the multiple-layer supporting method has been applied for this tunnel as reported in our previous paper mainly on the failing behavior of the first-layer supports and its numerical analyses. Further severe squeezing phenomena occurred in the shear-disturbed zone located at around the boundary between Konari and Itakura work sections. In this paper, the improvement of the multiple-layer supporting method in this zone is described including the predictive numerical analyses and the application results.