Abstract

Hydraulic tunnels are the most important structures for the proper operation of a dam, and especially diversion tunnels are designed to play a dual role. In particular, during its construction ensure dry conditions, while are also used as water intake tunnels or even evacuators during the operation phase of the project. However, both the type and the construction rate of the dam are crucial components in the design of the diversion tunnel, while this rate influences the return period of both hydrologic and hydraulic calculations. From the perception of construction, the drilling of the diversion tunnel may be easier via mechanical methods, but from the economic point of view it may not being so efficient. The aim of this research is the techno – economic comparison of conventional and mechanical methods of tunneling, and more specifically the drill and blast method and the use of micro – TBMs. To explore the multiple practical challenges from a real - world perspective, we are taking advantage of the Triantafillia Dam, located in Greece, which is characterized by an interesting geological gneiss underground. In analysis, hydrological and hydraulic models are employed, while the geotechnical design of the diversion tunnel is applied, accounting for the engineering geological characteristic - “keys” of the surrounding rock mass. Starting from the influence of the type of the dam on the required diameter of the diversion tunnel, considering the time required for its construction and the probability of failure, the alternative diameters of diversion tunnel are decided.