Buenos Aires Metro Line H, in Argentina runs N-S, at the west side of the city's downtown area. An extension of the line started in 2011. A TBM tunnel and one cut&cover station will be built southbound in estuary soft holocene soils; a NATM tunnel and three cavern stations are being built northbound in stiff cemented silts and clays. The experience accumulated in the last fifteen years has allowed for continuous advancements in the construction methodologies used for tunnels and underground caverns in stiff soils. Nowadays, the Line H northbound caverns - approximately 135m long and with a +200m2 face - are being excavated full face with excellent performance, far better than previous experiences where more conservative, staggered excavation procedures were employed. In this paper, the evolution of the NATM techniques in Buenos Aires´s big metro caverns is reviewed; the advanges and disadvantages of the changes in procedures are discussed and different optimization alternatives awaiting to be developed are described.
