坪林隧道施工地质探查技术之应用

Application of geological survey technique during Pinglin tunnel construction

北宜高速公路坪林隧道施工遭遇断层破碎带及大量涌水问题,为探查隧道前方的地质情况,以降低地质不确定引致之灾害风险,施工中应用了水平长距离钻探、震波探测与地电阻影像探测等地质探查的方法及技术。由于施工中地质探查结果知四棱砂岩段属特殊恶劣的地质条件,其工程地质特性为完整岩石非常坚硬,强度达220MPa,但在板块运动挤压作用下形成破碎带,其中夹有许多宽度小于1.5m的剪裂带,呈不规则分布的高低角度剪裂带,破碎带因地下水补充而形成含水层,含水层又因剪裂带构造密集复杂而被阻绝隐藏于背后,很难于施工中准确予以界定。文章将探讨应用于坪林隧道施工中地质探查技术的结果及限制、产生的问题与困难及相关因应措施,藉以累积施工地质探查的技术与经验。在四棱砂岩中隧道施工所获经验显示,必须综合应用隧道前方震测法(TSP)、地电阻影像探测法(RIP)、水平长距离钻探、短距离钻探等探查技术,先获得开挖面前方大范围的地质构造与水脉分布,再由水平钻探结果分析、研判与验证,方较能掌握隧道前方较准确的地质与水脉状况。

During the construction of Pinglin tunnel on Beiyi expressway, the fault, fractured zone and water flow are all encountered. In order to probe into the geological condition in front of tunnel face to reduce risk due to geological uncertainty, various kinds of survey methods and technology have been applied, such as horizontal long distance drilling, seismic wave survey and ground resistance image probing. The geological survey shows that the geological condition of Silen sandrock section is very poor, which is characterized by intact hard rock with strength of 220 MPa. Moreover, fractured zone occurs due to the movement and squeezing of blocks, among them some irregular shearing belt with a width of less than 1. 5m and various angels are discovered and they, full of groundwater, are isolated at the back due to the density and complexity of fractures. In this paper, the outcome, limitation, problems and difficulties as well as corresponding measures regarding the application of geological survey technology during Pinglin tunnel construction are discussed, which can enrich the experience of geological survey.