ABSTRACT
Los Cóndores will be a hydroelectric plant in Chile with an installed capacity of 150 MW. As part of the project a headrace tunnel (length 11 km) is excavated by means of a double shield TBM with an excavation diameter of 4.56m. After 1300 m in which a daily production up to 25 rings/day was reached the TBM blocked due to a fault zone with particularly poor geomechanical characteristics and significant water flow rates. Two different solutions have been proposed and developed for the unlocking of the TBM both aimed at the improvement of the mechanical characteristics of the soil at the front of the TBM. The paper shows how the analysis of all the potential technical risks has allowed to provide useful indications for optimizing the design and the operating procedures and minimizing the identified risks.
