This thesis describes in a practical and didactic approach ,the vital role played by geological engineering to the design and construction of the Turkwel Underground Structures, in a special context , where a single ,relatively small team from the Consulting Engineer was continuously involved in the preliminary and feasability studies,in the detailed studies and in the supervision of the works : i.e. excavations,supports and lining of tunnels and underground caverns. The flrst part describes the Turkwel hydroelectric scheme and the organization of the Consulting Engineer; the second part describes the geological background of the project and sets out the main results of the feasability and preliminary studies ( carried out before 1986 ); the third part describes the geological studies carried out during the detailed design studies and the underground works; the fourth part analyses the vital role played by geological Engineering to the design and works; the fifth part gives a general summary and puts forwards recommendations for a better use of geology in the deflnition of large underground structures.
