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  Development of the New Joint (SB Joint) for Shield Tunnels

  Traditionally most segments of shield tunnels built in soft ground like that of Japan are solidly connected by bolts. However, in the interest of eliminating the need for secondary lining, speeding up construction and decreasing costs, segments with smooth inner surfaces have become mainstream in Japan in recent years. Thus, various types of one-pass joints, by which tunnels are lined by simply inserting segments, have been developed. In the midst of this development, the authors of this report developed a new type of joint that uses screw bolts (“SB joints”) to fasten segment rings to one another. SB joints are one-pass joints that fasten segments through the insertion of screw bolts on the male side of one segment into multiple holes on the female side of another segment. Many tunnels in Japan have been built using SB joints. Japan experiences more earthquakes than any other country in the world, and memories of the Great East Japan Earthquake that struck in March 2011 are fresh. Research and technology development for the earthquake resistance of civil engineering structures is carried out every day. Earthquake resistance, seismic isolation and vibration control technology is being developed for shield tunnels. To date, elastic washers and other tools have been developed and put to practical use. However, elastic washers are expensive and, being elastic bodies that constantly exert forces, can cause creep and problems with water cut-off. Thus we improved on the technology by adding seismic isolation capacity to a new type of SB joint. Fixing elastic bodies of a certain stiffness to the insides of the female sides of the joints allows the joints to absorb displacement during earthquakes, and since the elastic bodies do not exert forces under normal circumstances, the creep and deterioration of water cut-off no longer occur. This report explains the fastening mechanism of SB joints, the basic testing done during their development, performance testing geared toward practical use and improvement by adding seismic isolation capacity.

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