Chile tunnel project for Robbins Crossover
By Catrin Jones06 January 2022
A Robbins XRE TBM 4.6m diameter Crossover machine bored a 3.3km tunnel in the Andes Mountains for Chile’s Los Condores Hydroelectric Power Project (HEPP) and project owner Ene.
The team, including three Robbins Field Service personnel, guided the machine to breakthrough in conditions including tuff, sandstone, breccia, and conglomerate with sections of high-pressure water inflows. The ground cover reached up to 450m above the tunnel with rock strengths maxing out at 60 MPa UCS.
For Riveros Puratic, project engineer for Enel, Crossover machines make sense despite the challenging conditions, “Towards the end, [the TBM] exceeded expectations. Crossover TBMs are suitable for Andean geology of sedimentary and volcanic type, where there is a great range of rock strengths and hydrogeological conditions.”
Maximum advance rates topped out at 605.8m in one month and 212.8m in one week.
The Crossover machine featured a heavy-duty, centrally mounted screw conveyor for the duration of the drive. The TBM remained in a hard rock configuration with a muck chute installed, along with paddles, bucket lips, scrapers and disc cutters on the cutter head.
However, “75% of the excavation was performed using the main drive gearboxes in high torque configuration (EPB or low-speed mode). We never physically changed the cutter head or screw conveyor to EPB mode,” said Omar Alvarez, Robbins field service site manager at Los Condores.
“During the segment ring installation, we stopped the water from draining through the rear shield drilling ports and we closed the screw conveyor rear gate. We reached 7+ bar in the cutter head earth sensors,” Alvarez added.