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:
- Phase 1: expected to be completed within 4 years after the start of construction (year 2018 in the estimated schedule):
- phase 1A is expected to be operational in February 2017 as it requires 3 years of construction;
- phase 1B is expected to be completed within 4/5 years after the start of construction (year 2018 in the estimated schedule).
- Phase 2: is expected to be completed in about 6 years after the start of construction (year 2020 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:
- a backfill consisting of silty sands with gravels and anthropically reworked materials;
- inorganic clay of low to medium plasticity and inorganic silt of low plasticity;
- silty sand;
- poorly graded gravel with sand, clay and silt;
- diorite, tonalite and philonian rocks.