out of sight - out of mind

Following on from my previous posts re onsite power generation and storage, I want to add an additional option to reduce above ground friction from land holders and vested interests from the “green factor”. Removing obstacles is always better than trying to work a way around them.

Global tunnel boring machine (TBM) manufacturer, Robbins created the Mining Development Machine they call the MDM5000. This machine is currently operating in the Fresnillo silver mine, Mexico.

Unlike traditional rock TBMs that bore a circular cross section tunnel, the MDM utilizes a reciprocating cutter head to bore a rectangular cross section tunnel (5m x 4.5m) with a flat invert. In this mine, the machine has bored at rates of up to 52 m in one week and 191 m in one month in andesite and shale with quartz intrusions that have defied earlier excavation attempts with road headers. Output per week (based on above figures) = 1170 cubic m.

The MDM5000 is a type of non-circular TBM developed for use in underground mining in rock up to 200 MPa UCS, particularly for long access tunnels and development drifts.

The MDM cutter head swings up/down about a horizontal axis that is perpendicular to the tunnel axis. Muck removal in the MDM is quite different from a standard TBM, with muck being pushed back from the cutter head on each down-sweep into a belt or chain conveyor installed at the invert. Essentially, loading of the conveyor is accomplished by the cutter head down-sweep rather than muck buckets emptying onto a belt conveyor as the cutter head rotates—the setup on a standard TBM.

The flat tunnel floor is beneficial as it enables the immediate use of rubber-tired vehicles for materials and crew transport. In comparison, if rubber-tired vehicles are to be used effectively in a circular bored tunnel, a flat roadway must be created by pouring a concrete floor or installing invert segments. The rectangular tunnel can be a smaller cross-sectional area to achieve the same useable roadway width. This means less material must be excavated and hauled to the surface to create the roadway tunnel.

The MDM offers a number of advantages for mines over other methods including drill and blast. MDM tunnelling has advance rates roughly twice those of a drill and blast heading, and results in smooth tunnel walls, less over-break, 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.
Using this equipment a vast majority of the mining and processing could be done underground, minimising surface land use, no blasting and dramatically reduced dust levels.

Is this an over simplification? – maybe, but it potentially removes some obstacles! Cost of set-up? Don’t know but should the price of silver beak free from the short positions, I doubt price would be an issue.

Watch this “Tunnel Talk” interview.
Here is the MDM5000 product brochure.