変状トンネルの覆工内面補強設計に用いる解析モデル化手法の提案

摘要

近年，供用後40年以上も経過したトンネル構造物が増加しており，その維持管理が急務となっている．とくに矢板工法により施工されたトンネルの多くは覆工の背面に空洞を有しており，近接施工や時間経過に伴う周辺岩盤内の緩み圧・塑性圧の増大により，剥落や岩塊崩落などにつながる可能性がある．このようなトンネルの補強設計においては覆工をフレームで，周辺地山を地盤バネでモデル化する骨組み構造解析が一般的に用いられている．しかし，骨組み構造解析では地山と覆工との相互作用を考慮できない欠点がある．そこで，本稿では緩み圧の作用による覆工の安定性への影響を考察できる数値解析モデル化手法を提案する．また，近年高性能トンネル補強材として用いられているFRPグリッドによる補強工法を対象として，緩み圧に対する補強効果と適用条件を有限差分法解析により解明し，考察を加える．%In recent years, the number of tunnel structures that have been in service for 40 years or more has been increasing and maintenance of these is becoming urgent task. In particular, many tunnels constructed with the timbering support technique have voids behind the lining and it is possible that this may lead to spalling or rock collapse due to an increase in loosening ground pressure / plastic ground pressure in the surrounding bedrock that comes from tunneling close by or the passage of time. In design of reinforcement for this kind of tunnel, frame model analysis that ground reaction is modeled as soil spring usually used. However, a disadvantage of frame model analysis is that it is not possible to take the mutual action of ground and lining into account. Therefore, this report proposes a numerical analysis modelling method that makes it possible to consider the stability of lining under loosening earth pressure. In addition, I clarified and investigated reinforcement effect and applicable conditions of lining reinforcement with the FRP grid that has been used in recent years as a high performance material for tunnel reinforcement using finite difference method.