CASE STUDY: LIMA METRO LINE 2

Project Description

The new Lima Metro line 2 is the first  underground structure project in Perù. The area where the Lima Metro line 2 is  located extends from Puerto del Callao (near the harbor) to Municipalidad de  Ate. The total length of the line is about 26.87 km and the tunnel length is  near 21 km, where 13.60 km are excavated with tunnel boring machine (TBM) and  the remaining with the new Austrian tunneling  method (NATM). The project includes 27 stations realized by Cut and Cover  method. The project  involves the realization of the first part of the Lima Metro line 4 (Figure 2),  totally excavated with TBM and the stations, also  in this case, are realized by Cut and Cover method. The  characteristics of the tunnel supports and the construction types of the  stations depend on geological and geotechnical conditions and on the possible  presence of water. 
The construction phase will be developed in two distinct phases:
  1.  phase 1A is expected to be operational in February 2017 as it requires 3  years of construction;
  2.  phase 1B is expected to be completed within 4/5 years after the start of  construction (year 2018 in the estimated schedule).

 Geological and Geotechnical Framing

The deposits in the project area were interested by different surveys, in particular  in the part of the line involved in the phase 1A: 16 drilling, 7 test pits (5  to 10 meters deep) in order to determinate the soil’s stratigraphy and 16 seismic tomographies that include seismic refraction lines (70 to 140 m length) and MASW in order to evaluate the seismic waves velocity and for the  acquisition of seismic profile, were performed.     
The investigations have shown the sequence  of these following lithological units (Table A) having different geomechanical characteristics: