Robbins MDM5000 makes headway at Fresnillo mine

A Robbins MDM5000, a rectangular tunnel boring machine (TBM), is making good headway to bore a hard rock tunnel with flat invert to access a deep underground orebody at Fresnillo plc’s Fresnillo silver mine in Mexico.
Robbins MDM5000 makes headway at Fresnillo mine Robbins MDM5000 makes headway at Fresnillo mine Robbins MDM5000 makes headway at Fresnillo mine Robbins MDM5000 makes headway at Fresnillo mine Robbins MDM5000 makes headway at Fresnillo mine

The MDM5000 - the MDM part of the name stands for ‘mine development machine' - has dimensions of 5.0m x 4.5m and can excavate a flat tunnel invert for immediate use by rubber-tyred vehicles.

It is progressing significantly faster than drill and blast excavation; it has advanced more than 1,700m so far at rates of up to 52m in one week and 191m in one month. The MDM5000 is excavating hard rock such as andesites and shales with quartz intrusions, and Robbins noted that these hard rocks have defeated earlier attempts to excavate these tunnels with heavy roadheaders.

The MDM5000 was developed for use in rock with uniaxial compressive strength (UCS) of up to 200 MPa, and is particularly useful for long access tunnels and development drifts. It utilises the disc cutter technology used on traditional, circular TBMs, and excavates a rectangular cross section tunnel with a reciprocating cutterhead and swinging cutterhead motion.

During its successful bore at the Fresnillo mine, the MDM5000 has undergone major component enhancements. First, it was transported to the mine's -695m level. Next, it underwent final assembly and launch in a cavern, where sections of the machine were moved by crawlers and pieces were lifted by hoist.

It is now boring a 270° spiral that will end above the original tunnel. Following this, it will be backed up to the original tunnel and continue driving straight ahead.

Robbins stated that the MDM5000 has several advantages over other underground development methods such as drill and blast. Compared to a drill and blast heading, its tunnelling advance rate is approximately twice as fast. It also excavates smooth tunnel walls with less overbreak and minimised ground support than blasted tunnels.

The company noted that the MDM5000's faster advance rates are partly due to its continuous progress, in contrast to drill and blast operations where the crew must exit the tunnel during blasting for their safety. The simultaneous ground support installation also further increases the overall advance rates, as opposed to drill and blast operations which must install ground support sequentially. 

The MDM5000 is the result of extensive discussions between mining equipment and TBM manufacturer Robbins, which designed and supplied the machine, with TOPO Machinery and Fresnillo plc. A video of the machine in action is available here.

Fidel Morin, projects superintendent for the Fresnillo mine, said: "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."

He added: "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 mining industry."

Robbins sees the MDM5000 as just one component of a new approach to underground mining with a multi-faceted solution for underground mine development. The company said this approach would utilise its shaft boring machines for ventilation and mine access, along with TBMs and conveyors to directly mine the orebody and transport material. These TBMs would be lighter, more mobile, and able to bore inclines.

Lok Home, president of Robbins, said: "It's all about reaching first ore quicker, and then economically mining the orebody while reducing tailings. Mechanised tunnelling machines have the potential to revolutionise the underground mining industry."

Robbins stated that its new solutions for underground mining are the latest in a "legacy of innovations" it has developed over the years, including "introduced equipment ranges from raise drills to non-circular mobile miners to continuous conveyors and customised tunnel boring machines at projects including the Grosvenor mine in Australia, the Stillwater mine in Montana, US and others."