挪威海底隧道经验

NORWEGIAN EXPERIENCE IN SUBSEA TUNNELLING

海底隧道深埋于海水以下,因而在勘探、设计、施工和运行方面都比陆地隧道更困难。挪威在近30a来修建了40条海底隧道,积累了丰富的经验,形成了被称为“挪威海底隧道概念”的一整套技术。规划设计阶段要采用各种可能方法进行尽可能详细的地质勘探,尤其是海洋折射地震波探测,以提供基岩表面深度、基岩地质剖面等重要资料。影响隧道的稳定主要为断层和软弱带,因此,在地质勘探中确认断层和软弱带是极为重要的。施工时需采用精心设计的方法,包括减少每轮爆破的进尺及采用喷射混凝土拱肋、密集长锚桩等。典型的挪威海底隧道衬砌由作为支护的喷锚结构和自立的防水防冻的内衬砌组成。挪威海底隧道的衬砌都按排水结构设计,而不承受外水压力。渗水是海底隧道的最大威胁,施工期应随时了解掌子面前的地质和水文地质条件,超前探测孔和预灌浆是控制渗流的最佳方法,同时必须时刻准备处理可能发生的紧急情况。最小岩石覆盖厚度影响隧道安全和造价,必须慎重考虑,根据岩石条件、稳定要求、渗水量充分论证,大部分挪威海底隧道的最小岩石覆盖厚度都小于50m。海水的腐蚀性给海底隧道带来一系列的特殊问题,须认真对待。

Subsea tunnels are located deeply under sea. Therefore, they are more difficult in geological investigation, design, construction and operation than land tunnels. In the last 30 years rich experiences have been gained in Norway from constructing 40 subsea tunnels and the＂Norwegian subsea tunnelling coricept＂has formed. In the planning and design stage, careful pre-investigation is of critical importance. Extensive marine seismic refraction survey is the major method for investigating bedrock profiles and detecting fault, weakness zones and depressions, which are the major threats to the tunnel stability. Directional core drilling from onshore passes geological structures and obtains rock cores, therefore, direct evaluation of the rock conditions can be provided. Special rock support methods are needed in order to pass such weakness zones, including reduced blast rounds, bolt-enforced shotcrete rib and dense long spilling bolts. The lining of Norwegian subsea tunnels consists typically of sprayed concrete and rock bolts for support and free standing inner lining for water/frost protection. The lining is designed as a drained structure, sustaining no external water pressure. Cast-in-place concrete is used only in extremely adverse geological conditions. All subsea tunnels in Norway are excavated by drill and blast method. Inflow of sea water is one of the critical issues for subsea tunnels since there is no natural exit for the inflow water, and therefore, it is essential to know the geological and hydrogeological conditions ahead of face. Probe drilling and pre-grouting technique are the best ways to detect the water inflow and reduce it to the acceptable level. Even so, equipments and measures have to be ever ready to meet the emergency situation. The minimum rock cover is an influential factor to the tunnel stability as well as economy and should be evaluated carefully. A minimum rock cover of 23 m has been used, despite the Norwegian road tunnel standard requires more detailed geological investigation and special analysis if the minimum rock cover is less than 50 m. Problems related to in-leaking saline water, such as erosion of shotcrete and metallic parts, are special issues for subsea tunnels and need to be coped with seriously.