New Tools for Tunneling.
Nowadays, tunnels are getting longer, stretching under entire mountain ranges, and digging deeper beneath rivers and ocean inlets. The strides being made stagger the imagination. However, in mining, tunnels and tunneling don't inspire the same kind of awe. Tunnels are just the means to get to an orebody and so don't always get that much attention. Miners are pushing the limits of their equipment, for they, too, are going farther and digging deeper. And they might soon find that these new technologies fit well to help them do their jobs safer, faster, and cheaper.
Many of the tools that the construction industry uses to push the limits of tunneling to greater depths or faster advance rates, though, have not yet made the transition into the mining industry. Some pieces of equipment probably never will. The mining industry, for example, will probably never have much use for pipejacking equipment. Some tools just aren't suited for the hardrock environment, though sometimes, it's the size or cost that keeps them from being used within a wider range of applications.
One machine that has not been used much in mining, but which could have wide applications, is the small boring unit (SBU), essentially a baby tunnel boring machine (TBM). The Robbins Co. makes one that, supposedly, extends the pipejacking capabilities of utility and road-boring contractors. While these applications are not found in mining, these SBUs are also capable of chewing through harder rock, including limestones and granites. "Altered rock, though, presents greater challenges than fresh rock," said Tom Fuerst, Robbin's SBU product manager. However, altered rock, so common in mining, is a challenge to any drilling or tunneling operation.
Powered by conventional auger boring machines, the SBU can cut a hole through hard rock as small as 24 inches in diameter to as large as 72 inches in diameter. The unit consists of a cutterhead that is fitted with mini-disc cutters mounted on a high-capacity thrust bearing. It uses the full-face auger for cutterhead rotation and uses the boring unit for thrust. Because the SBUs measure no more than 15 feet in length, they can be steered, which provides good grade and line control. SBUs expand the application of auger boring machines. A unit can be welded to an auger casing, and depending on the size, a contractor can access the face to change cutters or remove obstructions. The spoils can be removed by an auger, a conveyor, or a vacuum. The units are faster than conventional drill-and-blast methods, though they are not meant to be used as a replacement. In South Africa, Anglo Platinum is conducting tests of some of the first SBUs made for the mining industry at the Bafokeng-Rasimone mine in the Bushveld Complex.
Robbins offers several types of SBUs and smaller TBMs. Its newest SBU is the Rockhead boring unit, which comes with many of the functions featured in larger TBMs, including an operator station, cutterhead stabilization, articulation, and laser guidance. An optional thrust package is available for better cutter control and for bore lengths of more than 400 feet. Its Small Bore TBMs range in diameter from 48 inches up to 86 inches, and are specifically designed for tunnel projects longer than 1,000 feet. These units also come with a gripper assembly to react to cutter thrust and torque. If the rock is strong enough, the tunnel can also be bored "bald," which means bored without any liner or casing. Such machines can perform in numerous applications, including ventilation, man-ways, and possibly drifting.
Adding to the Mix
Along with the large equipment, there is a host of ancillary products out there that make the task of tunneling more cost-effective, cleaner, drier, and safer. For example, Ohio-based Master Builders has introduced a new line of TBM products that can be used in both hard and soft rock environments and complement several advances in shotcrete technologies.
In hard rock, the new Rheocem TBM grouts are microfine cements designed to penetrate into joints, fissures, and pore spaces to provide a watertight seal for dry tunnels. The grouts are available for rock or soil injection, groundwater sealing, and ground stabilization, in various particle size values, sulfate resistance, and setting times.
Master Builders has also introduced new additives to improve sprayed-on concrete for several different environments in underground mines. For rock support applications, Meyco SA 160 is an alkali-free, liquid additive that controls setting and hardening times of sprayed concrete. Up to 12 inches can be applied overhead in one pass. Meyco TCC735 is a chlorine-free additive that ensures better hydration of the cement in both the plastic and hardened states. It reduces shrinkage and permeability, while enhancing density and compressive strengths. DelvoCrete, another non-chlorine additive, controls the hardening dynamics of cement, and can suspend hydration of wet shotcrete for hours, or even days, without compromising the quality of the material.
Other additives include fibers that add strength to the shotcrete. The company teamed up with SI Concrete Systems to make a polymer-based fiber that, according to the company, enhances the structural performance of sprayed concrete beyond the level that can be achieved using secondary reinforcement. In other words, it can eliminate the need for welded wire mesh, but still provide three-dimensional reinforcement. The fibers inhibit cracking and reduce sagging and sloughing in vertical or overhead applications. Another fiber, made out of steel, called Novotex FE 0630, eliminates the need to bend and tie rebar and mesh in shotcrete applications, according to the company. All of these products can be applied with a robotic spray-mobile, which Master Builders developed especially for underground operations.
Safety remains a constant issue in mining and construction. Bad ground is onFEB24-1-137
Byline: Mike Chapple
TO borrow from that master of the macabre Edgar Allen Poe ... once upon a midnight dreary, while I pondered at the telly, weak and weary, I nodded nearly napping, when suddenly there came a tapping at my chamber door.
It was my old friend, Merseyside's very own late, lamented Deryck Guyler, in his guise as that old misery Potter, the school caretaker, the only saving grace of duff TV comedy of the early 70s, Please Sir!
Knees akimbo with thumbs looped behind his uniformed lapels, he was yabbering dourly that things weren't as good as in the old days and the kids don't know what they're missing. This familiar lamentation ended in an especially elongated and wistful rendition of his catchphrase - so blatently pilfered in recent years by Churchill the insurance dog - ``Ho-o-o-o-o-o yus!''
As the years creep by, Mr Potter has become a more familiar visitor to the cobwebbed corners of the mind. So it isn't his appearance that's disturbing so much as that increasingly I've found myself nodding in agreement to what he's had to say.
This latest occasion came as recently as last week when a far more unwelcome visitor The Brits - the perfect advert for all that's unadventurously barren about this country's insipid pop music scene - crept like a silent but smelly one onto the screen.
Hosted by by the hypnotically horrible Davina McCall - who looks and acts embarrassingly like a best mate's tipsy mum stumbling around looking for illicit feelie-feelies at teenage parties - it was grim indeed.
From the dreary Coldplay - c'mon son, pass me the razor blade and I'll finish off the job - to the predictible cabaret of Robbie Williams and Will Young as Best Breakthrough Act (no laughing at the back) the sickly offering was wrapped up by those old favourites Tom `It's Not Unusual, er, Unfortunately' Jones and Kylie.
Ah Kylie. Beloved of little girls, big boys and the kitschy `so bad it's good' branch of the gay fraternity, she may have a lovely bum but no more of this classic pop nonsense, per-lease. If, as this country's major record companies whiningly believe, that plummeting sales of our pop artists is due to the VAT on CD sales then this provided ample evidence that they should think again.
Thankfully, respite came later in the unlikely form of Whispering Bob Harris and part two of the Best of Whistle Test and blistering live performances from Bob Marley and The Wailers, Rory Gallagher, the Sensational Alex Harvey Band etc, etc. . . Shall we ever see their likes again? Sadly, perhaps no.
An old fogey? Ho-o-o-o-o yus - and proud. So there.
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|Publication:||E&MJ - Engineering & Mining Journal|
|Date:||Feb 1, 2003|
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