Innovative rectangular TBM makes headway in Mexico mine
By Jenny LescohierSeptember 08, 2021
A new rectangular tunnel boring machine (TBM) - capable of excavating a flat tunnel invert for immediate use by rubber-tired vehicles - is making good headway in Fresnillo Plc, Mexico’s oldest silver mine.
The Robbins MDM5000 (which stands for Mine Development Machine with dimensions of 5.0 m x 4.5 m) is working on a non-circular tunnel excavation in hard rock. It’s boring a mine access tunnel in andesite and shale with quartz intrusions that has defied earlier attempts using roadheaders.
“We decided to work with Robbins for their experience. A lot of people have tried to provide these kinds of machines but nobody has done it. Robbins used their experience and their skills to provide us with a rectangular profile machine,” said Fidel Morin, projects superintendent for Fresnillo Mine.
Rectangular tunnel boring machine
The technology is not only useful for the mining industry, but also for many applications in civil tunneling. While other machines have been developed for soft ground, the MDM5000 represents the first successful foray into rectangular hard rock tunneling.
“We’re very pleased to add non-circular tunneling to our wheelhouse of solutions that continues to include TBMs, conveyors, cutters and
more. We see applications for the MDM wherever a rectangular profile is needed, such as train tunnels requiring a flat invert. In a traditional circular tunnel, the invert is filled or an invert segment is needed, but with the MDM, 30% less rock is required to be removed from the profile,” said Robbins President Lok Home.
With more than 1,700 m of advance so far, at rates up to 52 m in one week and 191 m in one month, the MDM is significantly faster than drill and blast excavation.
“We’re making history. Fresnillo is always looking for new technology, and we believe that the usage of the MDM5000 is going to be something extremely successful, not only for our company but also for the industry,” said Morin.
The MDM5000 has undergone major component enhancements during the course of its successful bore at Fresnillo mine. It was first transported to the -695 m level of the mine and underwent final assembly and launch in a cavern, where sections of the MDM were moved by crawlers and pieces were lifted by hoist. The machine is now boring a 270-degree spiral to end above the original tunnel. It will then be backed up to the original tunnel and continue driving straight ahead.
Developed for use in rock up to 200 MPa UCS, the MDM5000 utilizes disc cutter technology proven on traditional, circular TBMs. During excavation, a reciprocating cutterhead and swinging cutterhead motion create a rectangular cross-section tunnel.
Better than drill and blast tunneling?
The MDM offers a number of advantages over drill and blast. MDM tunneling has advance rates roughly twice those of a drill and blast heading, and results in smooth tunnel walls, less overbreak, and minimized ground support.
The increased advance rates are partly due to the machine’s continuous progress, unlike drill and blast operations where crews must exit the tunnel during blasting for safety.
In addition, simultaneous ground support installation further increases overall advance rates compared with drill and blast
operations that must install ground support sequentially.