The Puclaro Tunnel is located in the Coquimbo Region on international Route 41-CH. It lies 16 km to the east of the town of Vicuña, on the section of road bordering the Puclaro reservoir, built in 1996. The road winds sharply, and the tunnel cuts through a steep outcrop of mountainside to which one end of the main Puclaro dam is anchored. The tunnel is 380 m in length and 8 m wide, affording space for a two-lane, two-way road paved with asphalt. The roadway is flanked by wide curbs on either side to permit higher than normal vertical clearance; this was engineered into the project to compensate for the lack of alternative routes and allow the passage of oversize loads. Such loads often pass through the tunnel on their way to the numerous astronomical observatories located in the area, generally in the form of large, indivisible parts and pieces, such as mirrors. The works also involved the design of a special lighting system for each of the tunnel’s portals, minimizing light pollution.
The tunnel passes through good quality igneous rock, which presented no problems during drilling and blasting. The excavation front moved from west to east, and false portals were added in precast concrete. Full-face excavation was the method used for almost the complete length of the project, and neither support nor special reinforcement was required for the excavation walls, with the exception of isolated bolts on some block fractures.