In recent years, there has been an increase in the number of railway mountain tunnels built in shallow ground. It can be said that such tunnels are susceptible to earthquake damage as the ground they are constructed in is soft. Since tunnel structures are assumed to be strong against earthquakes, no earthquake-resistance evaluation methods are generally put in place for them. Against this background, the RTRI proposed an earthquake-resistance evaluation technique involving model tests and numerical analysis.

For tunnels located in shallow ground, the RTRI replicated actual earthquake damage in a model test (Fig. 1), elucidated the mechanism behind earthquake damage and ascertained the earthquake resistance of tunnels and the effectiveness of seismic countermeasures (Fig. 2). The execution of such countermeasures (backfill grouting) on a tunnel with a defect in the test revealed that shear distortion in ground where compressive cracking (flaking due to bending compression failure) occurs in tunnel concrete lining amounts to about twice that seen before countermeasures are taken. Next, the RTRI developed an analysis technique to represent compressive cracking, conducted earthquake damage prediction for actual tunnels, and further confirmed the effectiveness of seismic countermeasures such as backfill grouting, fiber-reinforced concrete tunnel linings and the like.

Based on the results of the above, the RTRI proposed an earthquake-resistance evaluation technique for railway mountain tunnels located in shallow ground (Fig. 3). In addition, the Institute documented the proposed evaluation technique and organized it as the Manual of seismic countermeasures for Mountain Tunnels.

Part of the research was implemented according to “Program for Promoting Fundamental Transport Technology Research”.