Robbins Crossover TBMs in New Territory
Sep 30, 2015
First Rock/EPB TBM in North America represents an Evolution in Design
The XRE TBM is capable of “crossing over” (X) between two modes, rock (R) and EPB (E), and its fine-tuned design represents a new generation of Crossover machines.
Variable ground conditions necessitated the contractor’s choice of a Robbins Crossover TBM. The 5.9 km (3.7 mi) tunnel consists of sections ranging from fairly competent to weathered volcanic rock, soft sands, and clays. While standard TBMs tend to lose efficiency in these kinds of variable conditions, the Crossover TBM is equipped with special design features to tackle the mixed ground.
The design of the TEP II machine was based largely on experience from past Robbins projects, in particular the Kargi Kizilirmak Hydroelectric Project in Central Turkey. At Kargi, Robbins supplied a 9.84 m (32.3 ft) diameter Double Shield TBM, based on initial geologic reporting of fractured hard rock. Within 80 m (260 ft) of launch, the geology became substantially more difficult than expected, consisting of blocky rock, sand, clays and water-bearing zones. The machine required multiple bypass tunnels and major modifications before it could resume excavation.
The contractor at TEP II is confident about the machine’s abilities, which are optimized for hard rock but with many EPB characteristics: “In my opinion, the best part about the design of this TBM is the cutterhead; it is very robust,” said Sebastián Gallego Murillo, TEP II Production Manager for PROACON. He added that the biggest challenge would come near the end of the tunnel drive: “We expect to convert [from hard rock] to EPB mode due to the soils in this area. We will need to change out the cutters and modify the cutterhead.”
- The 8.7 m (28.5 ft) TBM for Túnel Emisor Poniente II is the first Robbins Crossover TBM to be used in North America.
- The XRE TBM is a Crossover (X) between rock (R) and EPB (E), and includes features of both a hard rock Single Shield machine and an EPB.
- The Robbins XRE was successfully completed using Onsite First Time Assembly (OFTA) at a jobsite in Mexico City.
- The 5.9 km (3.7 mi) tunnel consists of incredibly complex ground conditions, from competent to weathered volcanic rock, clay, and sand.
- The XRE TBM is part of a new generation of Crossover machines, designed with field-inspired features including single-direction cutterheads, multi-speed gearboxes, and improved probe drilling capabilities.
- Túnel Emisor Poniente II will relieve overtaxed wastewater lines in three key municipalities home to 2.1 million people. The areas are prone to wastewater overflows of 2 m (6.6 ft) or more during the region’s rainy season.
Click here, to see a drone footage video of the Crossover TBM assembly and launch ceremony.
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