Engineering Geological Studies for the New Drainage Tunnels of Lisbon

Abstract

The municipality of Lisbon is currently planning the construction of two drainage tunnels in order to control the periodic flooding that occurs in the city during the winter. The first tunnel is 5 km long with DN5500 diameter, crossing the downtown in a NW-SE direction and probably will be constructed by TBM. The second tunnel is located in the north part of Lisbon. This tunnel is 1 km long and is planned to be constructed by TBM or by NATM. The first tunnel crosses volcanic rocks and calcareous rocks from the Cretaceous and then detrital and calcareous rocks from Miocene. The second tunnel only intersects Miocene detrital and calcareous rocks constituted mostly by sand, silty sand, clay and biocalcarenite.For engineering geological characterization of alignments of tunnels, a site investigation program was planned and carried out that included boreholes, in situ (SPT, self boring pressumeters tests, packer tests, pumping tests and crosshole test) and laboratory tests (index, oedometer and triaxial compression tests). An integrated analysis of the data obtained from the site investigation works was performed in order to define the engineering geological conditions along the alignments of the tunnels.