This paper describes a case study involving 23.5 km of water supply tunnel in carbonate rocks. The process of excavations and the water flow become extremely problematic due to the existence ofkarstic regions along the tunnel route and also because of big springs in the area.
Along with population growth and technological developments, there has been an increasing demand on the construction and use of tunnels. Long tunnels such as Seikan (Matsuo. 1986) and British Channel (Howcraft. 1990), among others, are examples of such demand. In designing a tunnel, the shape, dimensions, and depth of the tunnel can be considered as important factors besides rock mass (Sinha. 1989). But in the case of long tunnels, such as Seikan and British Channel, which are constructed under the sea, the consideration of te1''l''ain conditions can also be of vital importance. Experience gained in the construction of these two tunnels is very valuable and can, therefore, be used in long-tunnel constructions presently under way. There has always been the question of whether the diameter of a tunnel should be given the first consideration or its length. As far as stress is concerned, the diameter can be given the first priority, but when we come to problems such as ventilation and operational difficulties, we can not underestimate the importance of the length factor.