PRESENT STATUS OF SEIKAN UNDERSEA TUNNEL

Construction of the 53.85 km long tunnel linking the islands of Honshu and Hokkaido commenced in 1972. Progress as of May 1977 is illustrated by means of a diagram and tabulated data, which divide the construction into three sections. The Honshu onshore section is 13.55 km with a geology consisting mainly of andesite and tuff with intrusive volcanic rocks; the Hokkaido onshore section is 17.0 km consisting of tuff of the so-called Kunnui strata; an offshore section of 23.3 km under the Tsugaru strait with a geology consisting mainly of mud-stone of the Kuromatsunai strata. Reference is made to particular construction problems associated with the length of the tunnel itself and the dangers of seawater flooding. Information is provided on the techniques employed to combat flooding and assist construction which included pilot tunnels approximately 19 sq M; service tunnels almost the same size as the pilot tunnels, 30 M away from the main tunnel route; advance boring with a range of from 500 to 1000 M; feeler drilling of from 70 mm to 90 mm driven 70 to 100 M in advance of the cutting face; chemical grouting and shot-creting. Details are provided of progress related to geological faults and flooding. The tunnel is designed to carry both standard gauge and narrow gauge railway track.