卵砾石地层中未固结砂岩夹泥岩隧道施工期开挖破坏模式之案例探讨

The Study of Tunnel Excavation for Un-consolidated Sandstone with Laminated Mudstone Demolition Model in the Gravel Deposits Layer

未固结地盘在工程地质学上并无一致性的定义,一般而言大致可对应于ISRM地质材料强度分级表中之R0～R2级别,并以岩心单压强度小于25MPa做为划分参考基准;所探讨的未固结砂岩夹泥岩地盘是以位于台湾西北部麓山带之林口砾石层及以砂泥互层、胶结松散砂层为主之大南湾层、观音山层为标的,并以位于该地层区域之某山岳隧道为例(以下以G隧道简称),探讨其中依据"台湾地区岩体分类与隧道支撑系统"所建置之砂质含量大于50%,岩类级别为CⅡ(S)之软弱地盘在隧道开挖过程中因地盘胶结松散、遇水易软化之工程地质特性而导致开挖各种破坏模式,藉由笔者及其它单位之数据以供工程界进一步了解此类型未固结软弱岩盘之山岳隧道设计及施工应考虑之因素,以降低施工期间之灾害风险。

There' s no general definition of Un-consolidated rock in engineering geology field. Normally, it defines with ISRM geology material strength from R0-R2 and it' s also divided with single compressive strength of rock core, which is less than 25 MPa. , This article discusses the gravel located in Lin-Ko, and poorly consolidated sand layer, and Inter-breeded Sandstone and Mudstone, located in Dananwan and Kuan-Ying Mt as the research object of this paper. Also, we takes one of the tunnels (G tunnel as following) in that area as an example to analyze the possibility of Demolition Model while encountering low-strength, poorly consolidate capability, and easily soften material during the process of excavation in CⅡ(S) tunnel, defined by Public Construction Commission Rock Mass Classification System (PCCR-System). It further provides the construction filed to have some general idea to design and construct weak rock in tunnels and decrease the risk during construction period.