Large highway tunnels under operating metro lines in the soils of Santiago – Design and Control approach

The Américo Vespucio Oriente II Concession (AVOII), part of the Urban Transport System of the Metropolitan Region of Santiago, Chile, includes the closure of the 65 km Américo Vespucio Ring in highway standard. The project involves the construction of two mostly parallel urban soil tunnels 5.2 km in length and three lanes in each direction and it will run below the existing Américo Vespucio Avenue. At the same time, it goes below the underground Metro Line 4 currently in operation. Skava Consulting SpA was hired by Metro as an expert reviewer of underground and surface works. The objective is to ensure that the existing Metro structures will not be affected by the construction or the operation of AVOII. The work involved highly complex 3D models. In search of a more efficient way to review the design, it was agreed to do finite difference models in the critical areas of the project. A total of 32 proper models were created. All of them proved to be useful in validating and correcting findings or deviations in the original design. Considering the above, and that the project runs at depths of 40 m in average – which for Santiago soil is uncommonly deep – it faces the challenge of an extremely low tolerance for disturbances in the surrounding ground. For this reason, specific subway rail deformation criteria must be fulfilled, and the surface and subsurface deformations must be monitored very frequently during the construction of the tunnel, due to commence in 3Q 2023.