About 30% of JR's tunnels are concrete block tunnels constructed before 1930. As some of these tunnels have degraded due to the deterioration of joints or the effects of ground pressure, an appropriate method of maintenance and management has been called for. However, no methods have yet been established to evaluate the strength of these tunnels in consideration of their specific dynamic behavior.
      It is important, therefore, to assess the behavior of concrete block tunnels when subjected to external forces. Thus, the RTRI tested a 1/30 scale model of a complete tunnel and a 1/2 scale arch section model under a load (Fig. 1). These tests showed that sound concrete block tunnels had the same strength as unreinforced concrete tunnels, and that voids behind the lining, thin joints, and other structural defects would significantly affect the strength and deformation characteristics of tunnels. The RTRI was thus able to assess the dynamic behavior specific to concrete block tunnels.
      The RTRI also developed a simulation technique to reproduce these tests by analyzing the frame structure of concrete block tunnels (Fig. 2), and quantitatively assessed the strength and deformation characteristics of lining and the effects of reinforcement work. Based on these study results, the RTRI proposed a method of evaluating the soundness of concrete block tunnels.

Fig. 1 Loading test on a 1/2 scale model


Fig. 2 Comparison between experimental and analytical values

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