Construction of a challenging new sewage tunnel in Mexico City has celebrated a major milestone with the first breakthrough on the project into an intermediary reception shaft.
The Túnel Emisor Poniente II scheme is the first in North America to use a crossover tunnel boring machine (TBM) to deal with hard rock and soft ground conditions on the alignment.
Main contracting join venture Aldesem, Proacon and Recsa is using a Robbins XRE TBM to drive the tunnel. The alignment of the 8.7m diameter tunnel includes excavation through andesite and tuff with cover of up to 170m through to soft ground with fault zones and cover as shallow as 8m.
“The geological profile of the project comprises six different lithologies, among them hard rock such as dacite,” said Aldesem’s Enrique del Castillo. “To get the best operation in both areas required use of dual mode technology such as the crossover TBM.”
The Robbins XRE machine has a canopy drill and positioner for enhanced ground consolidation, as well as gear reducers to adjust torque and RPM based on ground conditions. The TBM was initially launched in hard rock mode and will be switched to earth pressure balance mode later by switching out the belt conveyor with a screw and converting the cutterhead to undertake the final 874m drive on the tunnel.
Repairs will be undertaken in the intermediary shaft before the TBM is re-laucnhed to complete the drive.
The TBM was launched in August last year and is expected to complete work on the 5.8km long tunnel in autumn 2016.