The first hybrid Crossover TBM from Robbins breaks new ground in North America after emerging at an intermediate shaft on the Túnel Emisor Poniente (TEP) II in Mexico.
The 8.7m diameter Robbins XRE – a crossover (X) between a rock TBM (R) and an EPBM (E) – is now undergoing maintenance before continuing on to bore the final 3.2 km of alignment. The customized machine, for a consortium of Aldesem, Proacon, and Recsa, was chosen based on a number of parameters that included challenging ground conditions below an area to the west of downtown Mexico City.
The tunnel travels through a mountain under cover of up to 170m, through fault zones, before heading into a section where cover is as llittle as 8m above the crown. Geology consists of andesite rock with bands of tuff, and softer material in fault zones, as well as an 874m-long section in soft ground at the end of the drive.
“The geological profile of the project comprises six different lithologies, among them hard rock such as dacite,” said Enrique del Castillo for contractor Aldesem. “To get the best operation in both areas required the use of dual mode technology provided by the Crossover TBM.” The Robbins XRE is designed to allow the TBM to bore in both hard rock and mixed ground.
The machine setup includes 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, initially launched in hard rock mode, can be operated in EPB mode later on by switching out the belt conveyor with a screw conveyor and converting the cutterhead.
The machine began its journey in August last year (2015), and advance rates picked up quickly. Project records were set in January 2016 after the XRE achieved a best day of 42.8m and a best week of 185.1m. By mid-March the machine had bored through the first of the contact zones, a 30m wide section of fractured and blocky rock. While excavation through this zone was slow, progress picked up again in the more competent rock. Final breakthrough is expected in Fall 2016.
Once complete, the 5.8km tunnel will supplement an existing and overstretched wastewater line built in the 1970s. The deep drainage tunnel will serve to prevent recurrent flooding in Valle Dorado, and will benefit the cities of Cuautital Izcalli, Tlalnepantla, and Atizapan de Zaragoza, an area with a total population of 2.1 million people.