On the 14th September 2015, Ferrovial Agroman Chile completed the excavation of the subway tunnels (Section 2) of the new Line 6, which will form part of the Santiago de Chile subway. Line 6, which is fully constructed in a tunnel, has a total length of 15.4 km. Ferrovial Agroman
has been in charge of constructing Section 2 of Line 6 since January 2015. This section includes the construction of 2 stations, 2 inter-station shafts, 6 ventilation shafts and the inter-station tunnel, between these sections with an approximate length of 3,000 meters.Aside from the inter-station tunnel, the project includes two stations, two shafts, 196 meters of station tunnel and six ventilation shafts, all taken to sill plate level.The 125,000 m3 of underground excavation should be underlined, with the problem related to having to move excavated material outside the works to landfills of outlying locations, bearing in mind that the works are located in the center of a city with a population of over 7 million.For the construction of the Inter-station Tunnel, the New Austrian Tunelling Method (NATM) has been used, which consists of a cyclical and sequential process of traditional excavation, and at the same time, a primary coating is placed, which sufficiently confines the land until achieving the stability of excavation.At a later phase, the secondary coating is applied, in order to meet the service conditions of the tunnel.Excavation is performed through mechanical means. The coating elements consist of electro-welded mesh, reticulated frames and sprayed concrete, as basic support elements, with umbrellas in those special sections which require greater front confinement in excavation.The above has all been carried out with own staff, with a team of 380 people to carry out the works.The geotechnical complexity of this section has undoubtedly influenced the development of the project from the start, making it necessary to adopt corrective measures, as the work developed. This is shown by the more than 10 revisions and modifications of the first section of supports planned for the inter-station tunnel, based on the stratigraphy of materials to be crossed.We have therefore had to count on geology experts and specialists to check each development of the materials found, and to be able to determine the support to be used in the following length of excavation.