Aqueduct Tunnel in Masa-do

Abstract

The Gamagori Tunnel, wihch is one of tunnels under construction by the Aichi Irrigation Public Corporation, is a tunnel passing so-called “masa-do” an efflorescence consisting of granite, located at the end of the west main waterway of the Toyokawa Irrigation Project.
There is a layer containing under-ground water at the top. part of the tunnel. In making the location, a number of discussions were carrird out on that tunnel should be passed in this masa-do or tunneled into the hard rocks located in the north to avoid this or an open canal should be provided in the direction of the south.
As the results of various investigation, the construction was commenced after having judged to be quite safe to adopt normal construction method for excavating a tunnel into masa-do. But impossibility of progressing excavation has occured due to water flowing out with masa-do on the way of construction.
Finally, alternation of the construction method was obliged to adopt pressure construction method, its preparation now being progressed.
In this report, a consideration will be paid on in what cause was excavating a tunnel into masa-do determined and on the cause to have incured its failure.