Atlas Copco’s MineTruck MT 42 can discharge a full load in just 13 seconds.
Autonomous haulage may be on the horizon, but for now driver-operated trucks rule underground roads and ramps. Here are some ideas for optimizing fleet productivity.
By Russell A. Carter, Managing Editor
Despite a growing degree of interest in the advantages of autonomous mining, there’s no crystal-ball image available right now that depicts how underground haulage might look, say, in 10 years. But, as various computing, sensing, signaling and communications technologies converge and coalesce to advance the concept of driverless trucks, it’s likely that more than a few underground operations will try to benefit from the eerily precise and consistent behavior shown by autonomous surface haulage fleets.
Autonomous trucks in an underground environment aren’t new—Petra Diamonds has employed autonomous loading and haulage since 2005 at its Finsch mine, for example—and they aren’t common, but the trend towards unmanned haulers may be gathering momentum, pushed along by the industry’s desire to achieve faster mine development rates, provide a safer underground environment, and simply “get people off the site.”
Mechanical rock cutting concepts are currently bright objects on the rapid-development radar screen: Atlas Copco announced in March that in cooperation with Anglo American, it is set to begin testing this fall of a new type of underground mining machine that it described as “expected to transform the extraction process of ore from underground hard rock mines.”
In the same vein, Sandvik recently reported that it had commissioned a new, high-load hard-rock cutting test rig at its mechanical rock cutting competence center in Zeltweg, Austria—again, with a focus on investigating cutting technologies for application in rapid mine development and production schemes. Africa-based Randgold reportedly is working with Sandvik and an underground mine development contractor to implement a remote mining system at its Loulo mine in Mali, with an eye towards incorporating autonomous trucks and at least partially-automated mucking equipment.
Mechanical rock cutting, automated loading and autonomous haulage seem like a logical, hand-in-glove fit for underground projects with the right resources, geology and technical expertise, but for the time being and a number of years into the future, underground haulage will remain the domain of manned vehicles—complete with all the problems and advantages inherent in any activity that’s subject to human nature and workers’ physiological limits. And consequently, there’s no shortage of products, services or technologies designed to make manned haulage more efficient, safe and reliable. We’ll take a high-level look at several of these in the pages that follow.
Upstream in the underground mining sequence, it’s crucial that the loading tool used in combination with any mode of truck haulage is sized correctly or the operation will never achieve optimum efficiency. Proper truck sizing to accommodate underground conditions and the production plan is equally important.
For most underground operations, the primary loading tool is an LHD. Choosing the correct bucket type and capacity are critical, but industry experts advise that mine-workspace width and height are equally important defining factors. When selecting an LHD, mine operators must take into account not just the dimensions of the machine’s usual work space, but all spaces in which it may have to pass through to relocate, as well as identifying the ‘real’ height of underground work areas by noting any hanging ventilation or mine-service structures that could interfere with machine operation.
Likewise, a typical truck selection checklist could include a dozen or more principal concerns, including knowing drift dimensions, whether trucks will be loaded by LHD or chute, the density of the material that will be loaded, and if trucks are loaded by LHD, will they side- or rear-load? Does the mine layout lend itself to conventional dump bodies, or is an ejector body required? Open or closed cab? And which optional features and accessories will be conducive to improved productivity and safety, such as a payload management system, onboard fire suppression equipment or fast-fill fluid service system, for instance?
Underground mine-truck models recently introduced by the major suppliers have, for the most part, been diesel-powered and slotted at the high end of the capacity spectrum, and generally offer design improvements and feature lists that make it easier to tailor truck selection to a mine’s specific conditions and requirements, along with ergonomic upgrades that reduce physical stress on the operator and mechanical tweaks that improve reliability and safety.
Sandvik’s newest underground models—the 51-mt-payload TH551 and 63-mt-capacity TH663, both of which are lighter, faster and more fuel-efficient than their predecessors—now offer an optional onboard jacking system for faster and safer tire changing, after underground fleet operators pointed out that a loaded truck with a flat tire, stuck in the middle of a haulage ramp, can slow down or completely stop production for hours. On these Sandvik models, hydraulic jacks integrated at the front and rear of the truck can work independently of one another to facilitate lifting the machine for repairs. Also, a new tire pressure and temperature monitoring system now included on these trucks operates in real time, enabling identification of potential problems before they occur and reducing the probability of a usually disastrous tire fire.
Cat’s AD60 articulated dump truck, introduced at MINExpo 2012, is the largest in its line and features a C27 diesel engine that has been toughened for underground demands, including new pistons and high-temperature fuel injectors, more durable rocker arm assemblies, a redesigned crankshaft lubrication system, a high-efficiency engine oil cooler and a higher-capacity fuel cooler.
Dux Machinery Corp., which offers the DT series of conventional underground haulers along with its TD series Teledump trucks and ET series Ejector models, now can provide a Soft Ride Suspension System on many of its models, giving drivers a comfortable ride at higher tramming speeds. According to the company, the suspension is designed to withstand the rigors of severe mining conditions and improves operator and passenger driving comfort as well as safety on bumpy roads, reducing fatigue as exposure to high peak forces and vibration is minimized.
The system also is claimed to enhance vehicle handling at higher speeds, reducing cycle time and increasing productivity and efficiency while keeping vehicle wear and maintenance costs to a minimum. In use, the suspension’s progressive spring rate adapts for variable loads that start with normal machine operating weight, up to maximum payload without bottoming. Programmable controllers accept inputs for position, force and response, which can all be adjusted to varying parameters.
Road maintenance will be an important consideration for future operations using autonomous haulage, as real-time operator input about road conditions and problems will be absent. Rough roads wear out machinery, whether it’s manned or unmanned, but they can be efficiently rehabilitated with road graders specifically designed for underground work. Getman Corp.’s Road Builder grader, for example, is purpose-built to run in low-profile underground mining environments. The four-wheel drive unit employs a full grader blade that can be used for grading, ditching and material moving. It can also be equipped with an optional front push blade or rear scarifier, depending on specific operational needs.
The Road Builder is available with multiple cabin options for use in a variety of underground environments. Several camera options are available for improved visibility, and a variety of tire and cabin configurations can be specified for operations at different overall heights. Road Builder models protect workers through features such as a MSHA-certified operator compartment that meets ROPS/FOPS requirements, as well as matte-black painted surfaces to minimize glare in harshly lit, high-contrast underground environments.
Good haulage road systems need the kind of ongoing maintenance that road graders can provide, but as with all types of underground construction they must be based on solid surveying and mapping practices that provide consistently accurate data as a mine develops. Trimble and Peck Tech Consulting announced earlier this year that Trimble will distribute Peck Tech’s uGPS Rapid Mapper system, a new laser-based mobile mapping and surveying solution for underground mines. It can be deployed as a standalone mapping system or can be integrated with Trimble’s underground Mine Information System.
According to Peck Tech, the uGPS Rapid Mapper uses sophisticated mapping and filtering algorithms to provide accurate, georeferenced 3-D point cloud data faster than conventional mapping methods, and can be installed on any underground vehicle to generate point cloud data at normal operating speeds. Data is accessible via downloadable Wi-Fi, Ethernet or USB memory devices and can be imported to a wide variety of third-party software. uGPS Rapid Mapper is brand neutral to mining equipment and software for mounting on any underground mobile equipment. It can also be integrated with Trimble or third-party software applications and information systems.
uGPS Rapid Mapper, according to Peck Tech, is highly useful for conducting “will it fit?” surveys to determine whether large items of equipment can be moved from one point to another in a mine.
In another development with potential value for underground haulage, the Montreal-based technology consulting firm said it now has an effective platform for underground equipment localization. As it explained in a recent blog post, there are currently several types of technologies available to achieve localization capabilities. Wi-Fi and RFID systems, for example, position themselves based on proximity to the area’s nearest Wi-Fi access points and allow users to monitor any wireless assets over a mobile LAN.
While these types of technologies work well on the surface, they are less accurate and reliable underground, according to the company. This inaccuracy is due to a variety of different factors such as interference from the rock mass. These technologies are also difficult and expensive to maintain because they rely on the mine infrastructure—power cables, network cables, and access points—to operate.
Peck Tech said it has developed a solution to the underground localization challenge called the uGPS platform, which is claimed to provide underground operators with positioning accuracies comparable to L1 GPS and in a data stream format that is similar to common surface-based systems. It is infrastructure-independent, easy to install and integrates seamlessly with third party systems/software.
This technology, the blog post explained, has the potential to enhance underground fleet management systems that can take advantage of its high-accuracy positioning data for improved asset tracking.
Although the level of interest for underground fleet management systems is quite a bit less than for surface-oriented systems, fleet management solution suppliers such as RungePincockMinarco (RPM) have strengthened their flagship products to provide more underground operational capabilities. RPM released version 1.1 of HAULSIM only a few months after its formal market introduction, with greater capabilities for modeling underground hard rock mine haulage networks, giving users the ability to set more sophisticated road rules and configure haulage network features such as passing bays and ore passes.
Scoring with Simulation
Finally, studies indicate that one of the most effective methods for improving underground haulage productivity is to teach operators how to adhere to best practices, using equipment simulator training techniques.
As an example, a session with ThoroughTec Simulation’s CYBERMINE underground articulated dump truck (ADT) simulator continually monitors and records a trainee truck driver’s performance in terms of cycle times, processed tonnage, adherence to safety procedures, correct equipment handling techniques and response to emergency situations and sub-system failures. These performance reports, together with the instructor’s after-action review capability, provide a complete underground mine truck operator training and evaluation system, according to the South Africa-based company.
And, it’s not always necessary to begin with an elaborate simulation setup. “Our CYBERMINE CBT is proving popular, particularly in Africa and Latin America,” Richard Bellengere, executive vice president–operations at ThoroughTec, told E&MJ earlier this year. “This introductory level eLearning tool walks novice recruits through a particular vehicle’s basic controls and operation, as well as the environment, site operating procedures and safety checks.”
What is important, says simulator system supplier Immersive Technologies, is providing a unified training solution—which it has accomplished through its Training Systems Integration (TSI) services. The concept involves a partnering process that begins by “aligning expectations” between client and provider. Immersive can assist customers in ensuring that training objectives are chosen carefully and that training produces outcomes with the greatest return on investment. Under the TSI approach, while an internal ‘steering committee’ reviews key performance indicators, allowing the training function to compile information needed to update curriculum that targets performance gaps, Immersive’s TSI staff initiates reviews and updates the process, including analysis of training data and operator performance.
Paving the Way at Kiruna
LKAB’s Kiruna mine in northern Sweden is regarded as the largest and most modern underground iron ore mine in the world. Inside the mine, railway and road networks wend their way to a depth of 1,542 m. Lately, the mine has been using a machine not normally encountered underground—a track-driven asphalt highway paver—to smooth its 400 km of roadways.
When LKAB retained contractor NCC Roads to carry out underground paving and road repairs in the Kiruna mine, the company contacted Volvo dealer Swecon to determine if they could offer suitable equipment. Volvo CE provided the P7820C, which was then modified and moved underground. The whole process, from the first phone call to first asphalting, took only 10 days, which included the time to modify the paver.
Asphalt is mixed at a site located 17 km away from the mine before being transported underground. According to mine roads foreman Mathias Enlund, the task of laying it down has been made easier with the arrival of a Volvo Construction Equipment P7820C tracked paver. Almost all the paving is on inclined surfaces and the new paver is powerful enough to push 55-mt mining trucks delivering asphalt to the work site up 7% slopes.
“The P7820C had to be adapted to suit the particular conditions that exist down in the mine,” explained Svante Bodare, a road machinery product specialist at Swecon. “The underground tunnels are dark, the ceilings are low and the roads have a near constant gradient of 7%. So, we removed the roof of the paver, the exhaust pipe was shortened and extra lights were mounted on the machine.”
NCC Roads site manager Johan Pettersson claims the paver made a big difference in his team’s work. “When the equipment is unreliable, it really raises everyone’s pulse. This paver provides a whole different sense of confidence that we can carry out the work efficiently and without disruption.”
The biggest challenge, said Pettersson, was moving it at the end of a work shift—a slow process because the paver has a top speed of just 4 km/h.
Apart from laying a massive road network, the Volvo paver is also being used in the construction of new underground service and office areas. Iron-ore extraction is currently taking place at around 900 m, but the P7820C has been down to 1,480 m, where it has literally been paving the way for future operations.
“Around 20,000 tonnes of asphalt [was] laid underground [last] year, which is probably the largest amount ever in the history of an underground mine,” said Pettersson. “We would like to keep using the Volvo paver as it will be useful for road maintenance and there is a constant market underground.”