山岳トンネルは一般に地震に強い構造物といわれているが，既往の研究1），2）によれば地震の規模や震源からの距離によってはひび割れや庄ざ（曲げ圧縮破壊による剥離）などの被害が生じることがある。筆者らは，これまで山岳トンネルの地震被害の軽減を目的とし，山岳トンネルの地震被害の事例分析や，、地震被害メカニズムに関する研究を実施してきた3），4）。昨今，図1に示す既設山岳トンネルの地震対策工（裏込注入，ロックボルト，内面補強，インバート）が進められているが，これらの対策工の定量的な効果については不明な点が多い。%There are various seismic countermeasures for existing mountain tunnels such as backfill grouting to voids behind tunnel linings, installing of rock bolts to the roadbed, pasting of reinforcing materials to outside surface of linings and construction of an additional invert. In this study, the authors performed model tests and numerical analyses to clarify quantitative effect of these seismic countermeasures in poor geological conditions such as the fractured zone. According to the results of the studies, it has been apparent that inner reinforcement can control the initiation of the cracks and prevent spalling; backfill grouting can improve deformation performance of the tunnel and control the compressive failure at the arch crown; and rock bolts can control heaving of the roadbed. Moreover, there are a lot of restrictions on constructing an invert in the existing tunnel; however it has been apparent that the invert is a fundamental countermeasure to control the deformation of the tunnel and heaving of the roadbed.
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