ABSTRACT
This paper introduces the results of measurements made over a period of 12 years after the Seikan Tunnel was opened for service. Because this tunnel is a very long undersea tunnel, the necessity of clarifying the long-term behavior of the tunnel structure was recognized from the start. Various measurements are made to survey the condition of the ground and lining concrete and data thus obtained is used to assess the soundness of the tunnel structure. Judging from the data thus far obtained, the tunnel structure appears to remain in a good condition.
