Robbins unveils rectangular rock-mining innovation

2 September 2021


Robbins has designed and supplied an innovative machine which bores rectangular tunnels in hard rock, resulting in flat inverts that can be used immediately by rubber-tyred vehicles.

According to the company, while other machines have been developed for soft ground, the MDM5000 represents “the first successful foray into rectangular hard-rock tunnelling”. With compact dimensions of 5m x 4.5m, the MDM5000 (Mine Development Machine) is aimed at both mining and civil tunnelling.

“We see applications for the MDM wherever a rectangular profile is needed, such as train tunnels requiring a flat invert,” said Robbins president Lok Home. “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.”

Developed for use in rock up to 200MPa UCS, the MDM uses disc-cutter technology proven on traditional circular TBMs. In the way it advances through the tunnel, the machine is similar to a main-beam machine using grippers, propel cylinders and rear supports. The difference is in the cutting action: the MDM has a reciprocating and swinging motion working in the vertical direction to create a rectangular excavation; and the cutterhead is pushed into the rock by extension cylinders rather than by propel cylinders.

Robbins said the MDM5000 offers a number of advantages over drill and blast, including advance rates that are roughly two-times faster, smooth tunnel walls with less overbreak, and minimised ground support.

The increased advance rates are partly due to the machine’s continuous progress, said Robbins – unlike drill and blast operations where crews must exit the tunnel for safety during blasting. In addition, simultaneous ground support installation further increases overall advance rates compared with drill and blast operations that must install ground support sequentially.

The MDM is said to be making good progress at Fresnillo – the oldest silver mine in Mexico – where it is boring a mine access tunnel in andesite and shale with quartz intrusions that had defied earlier attempts using a roadheader. So far, the machine has advanced 1,700m at rates of up to 52m in one week and 191m in one month, rates deemed significantly faster than drill and blast.

Fidel Morin, projects superintendent for Fresnillo Mine, said: “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.” He added: “A lot of people have tried to provide these kinds of machines but nobody has done it. Robbins used its experience and skills to provide us with a rectangular profile machine.”

During the course of its bore at Fresnillo mine, the MDM has undergone major component enhancements. It was first transported to the mine’s -695m level and underwent final assembly and launch in a cavern, where sections of the machine 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.

The operation is the result of extensive discussions between Robbins, TOPO machinery and Fresnillo Plc.