Feasibility Study on the Applicability of a TBM for the Excavation of the 10km Long Diquís Hydroelectric Project Headrace Tunnel
The Diquís Hydroelectric Project is foreseen to have an installed power capacity of 631MW and is located in the southwest of Costa Rica in the General and Térraba rivers basins. The project’s headrace tunnel, which is due to transfer water from the upstream reservoir on the General river down to the underground powerhouse, in the vicinity of the Térraba river, is about 10.5km long and will have a finished internal diameter of 9.2 meters. The tunnel is expected to be driven mainly through sedimentary soft rocks such as claystones and sandstones, although the presence of some intrusive gabbros is also foreseen. Initially, the tunnel was to be excavated by mining methods with a horseshoe section; however, this paper presents the results of a feasibility study, focused on a detailed risk analysis, carried out on the applicability of a TBM alternative for the excavation.