By Ashley Karen
Works on Mexico’s oldest silver mine have been upgraded via the development of a rectangular profile hard rock TBM that could ease the civil infrastructure sector as well.
Robbins, the TBM (tunnel boring machine) manufacturer, worked with Fresnillo (a mine owner) and Topo (a machinery company) to develop the innovative machine to excavate along andesite and shale with quartz intrusions that have challenged earlier attempts to build new access tunnels using roadheaders.
The MDM5000 mine development machine, has the capacity of excavating a 5m wide by 4.5m high tunnel with a flat invert that can be used instantly by rubber tyred vehicles.
According to Fidel Morin, the Fresnilli project superintendent, this is the first successful rectangular hard rock tunneling machine to be developed.
“A lot of people have tried to provide these kinds of machines, but nobody has done it,” he stated. “Robbins used their experience and their skills to provide us with a rectangular profile machine.”
As Robbins declared, the new machines could be used for civil engineering applications. The company has also asserted that while other TBMs have been developed for soft ground, the MDM5000 represents the first successful strike into rectangular hard rock tunneling.
Lok Home, the Robbins president said: “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”.
Now, the latest machine has bored 1,700m of the tunnel at Fresnillo’s silver mine, with advance rates of 191m achieved in a month and 52m in a week, which Robbins has stated makes it faster than drill and blast techniques. Morin has described the tunnel boring machine as “making history”.
The MDM5000 has undergone essential component enhancements during the course of its successful excavation at Fresnillo mine. First, it was transported to the -695m 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 the hoist. Currently, the machine is mining a 270° spiral to end above the original tunnel. Then, it is going to be backed up to the original tunnel and continue driving straight ahead.
The MDM5000 which was developed for use in rock with a universal compressive strength of up to 200MPa, utilizes disc cutter technology proven on traditional, circular boring machines. During boring a reciprocating cutterhead and swinging cutterhead motion make a rectangular cross-section tunnel.
