Abstract

Huge earthquakes can pose serious risks even for rock tunnels, as evidenced by large earthquakes in the past. In a large earthquake in Japan in 2004, some tunnels suffered severe damages including collapse of their permanent lining, even though the tunnels were constructed in ordinary ground conditions. To mitigate such risks, countermeasures against earthquakes may be used where there are severe conditions such as faults, fracture zones, portals or extremely shallow areas, however, their mechanisms and effects are not fully understood. In this study, static loading tests were carried out assuming a ground deformation mode which simulated horizontal compressive deformation of surrounding ground caused by earthquakes, using a 1/20 scale model. The tunnel lining was laid in a soil container with countermeasures such as rockbolts, carbon fiber sheet on the inner surface of the lining and re-bar of the lining, in order to examine the mechanism of damages to the tunnel and the effects of such countermeasures. In addition, numerical simulations of the tests were conducted to clarify the effects of the countermeasures. The major conclusions of the tests and numerical analyses are:

  1. The loading test and the numerical model used in this study can be used to replicate the crown failure of the lining caused by horizontal compressive deformation of the surrounding ground.

  2. Rockbolts are less effective than expected in enhancing the load-bearing performance in the case of horizontal compressive deformation of the ground.

  3. Carbon fiber sheet and re-bar are potentially effective for avoiding major delamination of lining concrete.

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