The TBM boring the Los Condores Hydroelectric Power Plant has completed the 900m access tunnel and is working on the first section of the headrace tunnel. The machine, a 4.56m Robbins double shield, has so far excavated 1,300m.
The intake tunnel is excavated in two parts: the first one is a 6km drive and the second one is a 4.4km drive. A drill and blast section will connect the two drives, making a total 12km length.
The tunnel is located about 360km south of Santiago, Chile and is in the mountainous Maule Region. Overburden is 500m and two types of rock are expected to be encountered, sedimentary and volcanic.
The tunnel is lined with precast concrete segments measuring 250mm thick by 1.2m long in a 4+1 configuration. The TBM is currently advancing at a rate of 25 rings for every 20 hours of boring. Crews are working in two 10-hour shifts with one four-hour shift dedicated to maintenance.
The tunnel is 2,500m above sea level, and remote. The location of the work is a big constraint due to its rugged terrain and geographical location in the Andes.
To prevent tunnel deformation and collapse, hollow anchor bolt is generally adopted to support and reinforce. After excavation, rock and soil will decrease one side of force, hollow anchor bolt can then provide supplement. It combines drilling, grouting and anchoring together, makes excavation and support at the same time come true.