ASM
Surveying in Underground Mines
New underground surveying technology can change the way business is done.
Craig Dickson is a senior surveyor with GijimaAst, a company that specialises in IT solutions for mines.
Timing is everything in underground mine surveying. Get to the job too early, and the work can be washed away before the operators can use it. Get there too late and operators are standing down, at a cost. Waiting for a survey can be the bane of an operator’s existence.
Solutions to efficiency, cost and accuracy have been begged, borrowed and stolen from other industries, but at the end of the day, the surveyor is still behind the eight-ball – until recently, that is. New automation techniques are reducing the time lag in survey coverage and freeing up surveyors to attend to more of the statutory and regulatory issues.
Gijima Ast recently introduced a new system that incorporates software called Mine Markup, a Leica 1200 total station and a rugged tablet PC. It gives us the capacity to visualise and interact with the working area safely and accurately.
Plans for each level in the mine are automatically synchronised with the tablet from the main office server before every shift and taken into the underground environment where the work is to be done. The user can work from up-to-date designs of every level in all working areas.
We use the system to locate significant areas instantly, whether relative design centrelines, ore-body boundaries, or the location of services. It will even locate access points to the closest refuge areas.
The software uses a step-through system. One stage must be completed before the next can be activated. The set-up must be within a tolerance predetermined by the operation’s survey department. If the instrument is moved or the set-up is not accurate, the operator is not permitted to perform the next function.
It uses the resection method and wall station positions from a strongly maintained survey network. The process ties in seamlessly with existing metalliferous wall stations. Excavations are always resurveyed after the immediate mining task has been performed. High accuracy can be maintained and working areas kept safe, ensuring that the operation moves forward efficiently and with minimal interruption.
One of the system’s most important capabilities is its ability to locate and assess risks in real time. By creating a safe working sphere around the active excavation, other anomalies in the mine can be detected.
The safe working sphere is simply a measured sphere around the total station. If it comes into contact with any mapped items that the operator needs to avoid, it will alert the user. The entire history of the operation is on the tablet, reducing the chance of an unnoticed risk.
Voids, back-filled stopes, aquifers, exploration holes, other excavations – and even the crown pillar (rock between levels) – can be displayed as hazards. Once the location is established and the safe working area is approved, surveying can continue.
Having determined a safe location in the heading (tunnel), the operator is able to mark up the centreline and grade of the next excavation. The software then directs the laser to point at the correct field location.
It is no longer necessary for the surveyor to enter the co-ordinates and read the offset from design to mark up the next excavation. The software controls the theodolite laser pointer and will keep following the correct path until the operator has painted it.
Once the centreline is done, a push of a button marks up the grade line to the design floor.
Laser pointers inserted in the wall have been revolutionary in improving continuous mining and reducing the reliance on survey direction for every advancing excavation. Stationary wall laser guidance, however, still relies on the assessment and maintenance of an offset position relative to the laser location. It also requires the updating of current plans to reflect the excavation’s active position. This constant directing and monitoring of excavations greatly reduces the effectiveness of a surveyor in other mining and traversing tasks.
In civil tunnelling, the position of the active cutting plane of the tunnel boring machine or road header is the most important location on site. The total station is used for direction control. The software directs the driver to the centreline of the excavation at all times. Most importantly, this data provides information on where the machine is heading. Preparation is paramount.
The survey crew is responsible for the back-sight traverse, but the operator can use an onboard guidance system at any time to meet the shift’s requirements and plan ahead.
Until now, underground mining has never had such a seamless transfer of location data.
There is no room for error in tunnelling or mining. Any lag due to slow data transfer or inaccurate measurement can put an excavation offline and cause expensive redesigns or QA issues.
Safety, staying on design and keeping to the schedule are the most important elements in any operation. The role of the surveyor should be to maintain the accuracy of the reference traverse for the automated system, rather than spoon-feeding data to the machine and its operator.
An automated survey tool allows the operator to determine position easily and therefore create a continuous mining system. The ability to place the advancing machine in its true location with every excavation addresses the key issues.
There are also cost benefits for mine operators in survey automation. It helps reduce the extra height and width that might be taken by a less-monitored operator – this is called over-breaking. It reduces wastage of consumable materials such as bolts and mesh, and it ensures that accurate grade is always maintained and monitored. The bottom line: the operator is kept informed at all times, reducing rework and improving accuracy.
A less obvious advantage is that the system also improves the flow of data to other sections of the organisation. Geologists now have far more live data at their disposal when they make decisions. Data can be exported to most software at the touch of a button.
The benefits are exponential. Once executives have their eyes opened to the significance of accurate real time position in an underground environment, the possibilities for all departments – in saving costs safely – are endless.
