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High Cover TBM Tunneling in the Andes Mountains—A Comparative Study of Two Challenging Tunnel Projects in Chile

The Andes Mountain range is among the youngest and most complex in the world, geologically speaking. Tunneling projects, particularly for hydroelectric and water transfer schemes, are not new to the range but their past history has met with mixed success. Two new projects utilizing very different tunnel boring machines and excavation strategies are now providing a testing ground for modern underground construction equipment in the Chilean Andes.

This paper will analyze two projects: the Alto Maipo and Los Condores Hydroelectric Projects, located approximately 100 km apart in the Andes Mountains. The two strategies being employed will be analyzed in detail, as one project is using an open-type Main Beam TBM plus extensive ground support, while the other is utilizing a Double Shield TBM and segmental lining. The authors will look at TBM performance and ground conditions encountered in the two tunnels and what effects the TBM selection and ground support strategy may have had on each tunneling operation.

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