ABSTRACT
As part of the future circular line of the Lisbon Metro System, Estrela Station stands out for being the deepest in the network, with a depth of around 60m. Excavated using the NATM methodology from a shaft with quadrangular and circular sections in Miocene and Cretaceous limestone, it posed challenges inherent to this type of work due to its section size, geological singularities or the need to increase productivity. Production was optimized with the excavation of a pilot tunnel from the T33 track tunnel in order to have another front for debris extraction and also serving for geological reconnaissance. Intercepted rock faults, recognized or not in the previous design phases, were addressed in order to mitigate excessive deformations or even potential instabilities. The presence of the second unit of the “Caneças Formation” in the lower section of the station chamber, of a more marl-clayey nature and potentially more deformable, led to the adoption of complementary support solutions foreseen in the project, as well as specific reinforcements.
