含軽石火山礫凝灰岩地山における計測管理手法の提案: 北海道横断自動車道 天狗山トンネル

摘要

Tenguyama Tunnel is an expressway tunnel of 2,978m (outbound) in length located between the Otaru-Nishi (provisional name) Interchange and the Otaru (provisional name) Junction on the Hokkaido Odan Expressway. The geological condition of this tunnel is lapilli tuff containing pumice in Miocene of Neogene, the Katsunai-gawa formation, which has low uniaxial compressive strength and extremely high modulus of deformation. The correlation between uniaxial compressive strength of ground and amount of deformation was low. It was difficult to determine the effectiveness of supports depending on only standards for deformation in measurement management. This report contains information on the results of verification of validity of tunnel supports which make tunnel stability more reliable, using the relationship between apparent elastic modulus and overburden ratio or the relationship between apparent elastic modulus and strain in wall in these types of geological features.%天狗山トンネルは，北海道横断自動車道小樽西IC(仮称）～小樽JCT(仮称）間に位置する延長2,978m(下り線）の高速道路トンネルである.当該トンネルの地質は，新第三紀中新世（勝納川層）の含軽石火山礫凝灰岩であり，一軸圧縮強度は低いが，変形係数が非常に高いという特性を持つことから，地山の一軸圧縮強度と変位量との相関が低く，変位量の計測管理基準値のみでは支保工の有効性の判断が難しい状況であった.本稿では，このような地質における見掛け弾性係数と土かぶり比との関係や，見掛け弾性係数と側壁ひずみとの関係を用いることで，トンネルの安定性をより確実にする支保パターンの妥当性について検証した結果について報告する.