ABSTRACT
Yanango Tunnel is located in Junín, Peru; enhancing the connectivity between Lima and the Central jungle between Tarma and La Merced. The construction was awarded to a JV (MPM and Balzola) in a 25 MUSD contract, and took place from 2015 to 2016, and its inauguration was last September 2017. The tunnel has a length of 1,062m with three traffic lanes, in a section of the 96m2. The geology is composed by fair to good geomechanical quality granodiorites. The main challenge was the construction of both portals, requiring changes in their initial designs, constructing two false tunnels structures before starting the excavation. The Western Portal was excavated in colluvial soils, with only 15º between the hill side orientation and the tunnel axis. To ensure the stability of the lateral slope, a soil nailing was necessary as well as a heavy micropile umbrella.
The Exit portal is located in a vertical relief and competent rock mass. The solution adopted has been a previous bolting reinforcement and a sequential excavation of the tunnel: false tunnel, a transition section, and afterwards starting the tunnel excavation.
