瞬变电磁法在浅埋富水全强风化花岗岩公路隧道中的超前探测

Application of Transient Electromagnetic Method in Advanced Detection of Geohazards in Shallow Buried Highway Tunnel in Saturated Completely Weathered Granite Soils

针对景海高速公路马备脚隧道具有浅埋、偏压、富水和极软岩等特点,施工揭露隧道围岩主要以粉质粘土和全风化花岗岩为主,夹球状风化孤石,围岩自稳能力极差,流塑性强,施工扰动作用下围岩液化现象明显。施工中工作面涌泥、涌水、拱脚冒泥冒水、拱顶和边墙围岩冒落、塌方等现象多发。结合新建的景海高速公路隧道马备脚隧道工程,运用瞬变电磁法的原理分别在掌子面和地表处进行地层含水探测,并通过探测结果及时反馈信息,对浅埋富水全强风化花岗岩公路隧道的设计、施工起到了重要的指导作用,可最大限度的降低这些不利因素对隧道施工的重大影响,确保工程建设的顺利和安全。

The Mabiejiao Tunnel in the Jinghai Expressway project has the characteristics of shallow burying,unsymmetric pressure,rich groundwater,and extremely soft rock mass.The exposed geomaterials during the tunnel excavation consist of silty clay and completely weathered granite saprolite with individual less weathered sphere boulders.The stability of the surrounding rock is poor and small disturbance in the tunnel excavation could easily induce the liquefaction of the surrounding rock mass.Construction related geo-hazards,such as,rushing of mud and groundwater at the excavation surface and at the bottom of supported surface,rock collapse at the crest of arch and side walls,are frequently occurred.This paper presents a case history of applying the transient electromagnetic method to collect groundwater information at the supporting area and the ground surface in the Mabeijiao Hunnel of Jinghai Expressway.The collected data could be used in providing advanced hazard prediction and providing design and construction guidance of the shallow buried highway tunnel excavation in saturated completely weathered granite saprolite soils.The collected data could also minimize the impact of adverse factors on the tunnel excavations.