The Geological Investigation in the Gallery Under the Seikan Tunnel

Including Reconsiderations and Suggestions

Abstract

The Seikan Tunnel is located 100 meters below the seabed. The maximum depth of the sea above the tunnel is 140 meters, and there are strong currents of up to 8 knots.
Because of the considerable depth and the strong currents, there were limits to the types of surveys which could be conducted from the sea surface.
This was especially true of the central area of the straits, where both the number and precision of surveys were inadequate.
Thus, it was necessary to supplement these surveys with surveys conducted from within the tunnel.
The surveys were based mainly on pilot boring and daily investigation of the face.
It is believed that the Seikan Tunnel project was the first project in which these methods were used on a daily basis.
This report describes how underground geological surveys were conducted in the under sea tunnel during construction, explaining both the method employed and the results obtained. Furthermore, reconsiderations and suggestions from both the parties which conducted the geological survey and the parties which used the data from these surveys are also included.