STUDY ON FLOOR HEAVE AND ITS COUNTERMEASURES IN MOUNTAIN TUNNELS WITH CONSIDERATION OF THE INFLUENCE OF CONSTRUCTION

Some mountain tunnels in service suffer from floor heave, and some of them require countermeasures. It is considered that such floor heave phenomenon and the effect of its countermeasures are closely connected with the excavation method and tunnel structures, however no such numerical analysis study has been found. In this study, tunnel construction, floor heave during service and its countermeasures are consistently modeled in the numerical analysis. As the result, invert construction and early closure were found to be effective for preventing deformation not only during tunnel construction but also during service. Moreover, it was confirmed that in the application of rock bolts as a countermeasures to the floor heave during service, well-balanced specification of the bolts considering the surface bonding and yielding of the bolts is important for securing the long-term performance of the countermeasures. 山岳トンネルにおいて，供用開始後に路盤隆起が発生し対策工が必要となることがある．このような路盤隆起現象やその対策工の効果には建設時の工法や構造が少なからず影響することが予想されるが，このことについて数値解析的に検討した研究は見当たらない．そこで筆者らは，トンネルの建設から供用中に発生する路盤隆起，その対策工までを一貫して数値解析によりモデル化した．その結果，建設時のインバートの施工，早期閉合の実施が供用中の変状抑制にも効果的であることがわかった．また，供用中の路盤隆起対策工としての下向きロックボルトは付着切れやボルト材の降伏に注意しつつバランス良く仕様を向上させることで，ある程度長期的に効果を発揮することが可能であることを確認した．