Final breakthrough at Emisor Oriente in Mexico 06 Jun 2019

There was great celebration as the last of six 8.93m (29.3ft) diameter EPBMs completed excavation of the Mexico City Tύnel Emisor Oriente (TEO), a feat marking the completion of ten years and 62.1km (38.6 miles) of tunneling.

Robbins 8.93m EPBM completed the TEO final drive

The final breakthrough to complete Lot 4 of the project on 23 May 2019 was the latest milestone for the urgently needed wastewater tunnel that spanned some of the most difficult geology ever encountered by EPBMs. The 10km (6.3 mile) long Lot 4, running from Shaft 17 to Shaft 13 at depths of up to 85m (280ft), included sections of basalt rock interspersed with permeable sands with high water pressure. “Our machines had to go through the worst geology, but they were designed for it,” said Roberto Gonzalez Ramirez, General Manager for Robbins Mexico. Three Robbins EPBMs with Robbins continuous conveyor muck haulage systems were used on Lots 3, 4, and 5 of the project.

Despite multiple challenges, the Lot 4 EPB operation achieved a project record of 30m (98ft) in one day, and a high of 528m (1,732ft) in one month, due to the continuous conveyor system used for muck removal.

The machine achieved 30m/day and 528m in one month

“Our advance rates were achieved thanks to the Robbins conveyor design. The tunnel conveyor was composed with elements such as the booster, vertical belt, curve idlers, and advancing tail piece, as well as elements on the surface. Personally, I think this system helped us achieve the TBM performance,” said Carrillo.

“We are proud of having successfully finished the excavation,” said Hector Arturo Carrillo, Machinery Manager for Lot 4 contractor Carso Infraestructura y Construcción (CARSO). “Despite all the adversities we faced, including large inflows of water, hydraulic loads and constant changes in geology, we solved these by adapting the excavation mode according to each type of geology found.”

TBM launched on ambilicals and over two months at the 85m deep Shaft 17

Robbins crew celebrates breakthrough after boring through difficult geology

All three Robbins machines were designed for water pressures from 4 to 6 bars, with mixed-ground, back-loading cutterheads equipped to tackle variable ground conditions. High pressure, tungsten carbide knife bits could be interchanged with 17in diameter carbide disc cutters depending on the geology. Other features included man locks and material locks designed to withstand pressures up to 7 bar, a redesigned bulkhead, and Hardox plates to reinforce the screw conveyors with extra removable wear plates to further strengthen each screw conveyor flight. The rotary union joint was redesigned to improve cutter change times during cutterhead interventions, while a new scraper design offered more impact resistance in mixed ground conditions with rock.

The Lot 4 TBM was assembled in launch shaft 17 and commissioned in August 2012, with the bridge and all the back-up gantries at the surface. Two months later, in October 2012, after advancing 150m (490ft), the machine and its back-up were completely assembled in the tunnel. A month later, the continuous conveyor system was installed and running.

Continuous conveyors helped achieve steady advance in difficult geology

After 405m (1,328ft) of excavation, the presence of scrapers, parts of the mixing bars and other wear materials in the excavated muck prompted a cutterhead inspection. With high pressure up to 3.5 bars, it was determined that a hyperbaric intervention was necessary, and on 2 June 2013 the first hyperbaric intervention through an EPB TBM in Mexico was performed.

The interventions were costly and time-consuming, and after about 50 hyperbaric interventions the remainder of the interventions were undertaken in free air. “The interventions carried out in atmospheric mode were the biggest challenge,” said Carrillo. “The great influx of water tested the limits, because we were excavating on a decline. In all of these interventions we had to implement a double pumping system, at both the TBM and at the working shaft. Despite the challenges of pumping water at volumes of up to 180 litre per second, and cleaning fines from the tunnel each time the operation was performed, atmospheric interventions were still lower in cost and quicker than those undertaken under hyperbaric pressure.”

“Robbins were always present giving ideas and contributing experience to solve the problems,” added Carrillo. “One of the most recent examples, almost at the end of this project, was where the machine encountered a blockage to the shield and could not move forward. It became necessary to implement exceptional hydraulic pressure, reaching a pressure range of 596 bar on 28 thrust cylinders. Robbins personnel helped us during all that time and we were able to get through it.”