Field observation of the Baixa-Chiado Station, Lisbon Metro

The Baixa-Chiado station is part of the Lisbon Metro network and consists of two enormous cavities with a 240m(2) cross section each. It is one of the largest underground engineering works ever built in clayey and sandy soils. For its execution the NATM method has been used. The settlements predicted in the design were high, even though the differential settlements were considered insignificant, justified by the existence of limestone layers in the sand. After excavation of the first cavity, it was verified that the differential settlements were much higher than the values predicted. Thus increasing crackings in the old buildings at the surface. For that reason compensation grouting has been implemented in the excavation of the second cavity and thus the evolution of the settlements has almost ceased.