This is an edited excerpt from a paper that was originally presented at AusIMM’s Iron Ore 2019 Conference
At most hard-rock mine sites around the world, blasting is a critical process by which rock mass is broken into smaller pieces to assist mining of orebodies. During blasting, ore moves from its in situ position. The BMT designed blast movement measurement system is the only efficient way of discerning the final orebody location after a blast. The measurement system works by installing Blast Movement Monitors (BMMs) in a bench before a blast. During the blast, BMMs move with the ore and their final resting locations allow BMT’s bespoke software to accurately measure movement in 3D space and generate dig polygons for the mine site.
The process described above requires users to walk on the post-blast muck pile and locate BMMs using a hand-held detector. This can be dangerous due to presence of subsurface gas, voids, unstable grounds, blast tie-in debris and more. Some of BMT’s existing customers located in the arctic circle have to locate the sensors in treacherous icy conditions. There are also mine sites in Australia and around the globe that would like to use BMMs for blast movement monitoring but cannot do so due to their internal safety controls restricting access to post-blast muck piles.
To solve these issues, BMT embarked on an 18-month quest to find a solution to allow mining companies to experience the benefits of accurately measuring blast movement without having to walk on a post-blast muck pile. After vetting many different potential solutions, it was decided that BMT would develop a detection system based on Unmanned Aerial Vehicle (UAV) technology.
As part of developing the UAV-mounted BMM Detector, prototype testing has been conducted in mines in Australia and Europe. This article summarises the results from the most recent testing conducted at an iron ore mine in Western Australia.
The Blast Movement Monitoring system
The Blast Movement Monitoring system was developed and patented by the University of Queensland and commercialised under licence by Blast Movement Technologies. The system consists of transmitters, BMMs, which are placed within the blast area prior to blasting. The transmitters are then located after the blast with a purpose-designed detector and the acquired data is processed using BMTs bespoke software package to calculate movement of orebodies as a result of the blast. The complete standard system is comprised of:
- the Activator: a remote control that switches each transmitter on and programs it as required
- BMMs installed in dedicated drill holes within the blast that are then surveyed
- a purpose-built Survey-Enabled Detector (SED), also known as the GP5350, is used to locate each BMM after the blast and determine its depth
- BMM Explorer software calculates the 3D movement vector of each BMM. The data is stored in a database for future reference.
UAV-mounted BMM Detector components
Hardware – commercial ‘off the shelf’
The BMT UAV-mounted BMM Detector is designed for ease of assembly, replaceability and maintainability in mind. The following commercial ‘off the shelf’ items were selected for the BMM Detector:
- DJI M600 Pro Flight Platform with A3 Pro Flight Controller
- DJI DRTK GNSS system for precision navigation
- Trimble BD990 GNSS receiver with Trimble AV59 Antenna
- Pacific Crest radio module with whip antenna
- iPad-based ground station for flight planning and monitoring.
Hardware – BMT designed
The following BMT designed hardware was mounted on the DJI M600 Pro using the DJI Ronin MX Gimbal:
- Remote Processing Module (RPM) based on the existing GP5350 SED design
- Light weight coil antenna based on the existing GP5350 design.
Software – BMT designed
BMT has developed the following software packages to assist in BMM and blast movement calculation:
- software for ground station to enable mission planning and flight monitoring
- software to post-process acquired data to ascertain BMM locations
- BMT’s existing desktop software package BMM Explorer to calculate blast movement.
UAV-mounted Bmm Detector operation
When using the UAV-mounted BMM Detector, BMM installation is done using BMT’s existing SED. The install points are then transferred to the iPad and used as waypoints for the post-blast detector flight. In the prototype, the search for BMMs is conducted following a predetermined grid pattern with install points of each BMM assigned as the centre point of each grid. The grid dimensions can be manually set by the user before the flight, which are a function of the expected movement.
The system is fitted with three separate GPS systems, two of which are used for navigation. The detector uses the onboard DJI DRTK as the primary system for navigation and the standard GPS as a redundant active standby system. The third GPS system onboard is a Trimble GNSS receiver which is used to record BMM locations with centimetre-level accuracy. The detector system is also fitted with forward and downward facing lasers. These lasers are configured to pause the flight if either of them detects an object either in front of or under the UAV. If an object is detected, the UAV will pause and hover at the point of detection allowing the user to decide whether to continue or cancel the mission.
Before take-off, once all individual components of the UAV-mounted detector system are powered, the system does an automated pre-flight check. If all checks pass, the operator can send a command through the iPad to the UAV to start the mission. The UAV then automatically takes off and flies to the BMM install location and searches along the pre-planned grid for each BMM location. Once all grids are completed, the UAV automatically returns home (ie to the take-off location) and lands without any user intervention. An option is also designed into the system for the UAV to automatically return home if the batteries powering the UAV reach a charge level of 25 per cent. The point at which a mission is suspended is recorded in the onboard flight controller. The UAV can resume the mission once the batteries have been replaced.
Prototype testing at iron ore mine site
As part of developing the UAV-mounted solution, the prototype system was tested at an iron ore mine at Western Australia. Two blasts were monitored using a conventional SED and the new UAV-mounted BMM Detector. Following is a summary of results from each blast.
Ten BMMs were installed in five separate monitoring holes in Blast 1, and all ten BMMs were detected post-blast using the SED. Figure 1 shows a plan view of the blast, including the initiation point, timing contours, and centrelines. The numeric labels on the plan correspond with the corresponding BMM number. The blast was initiated in a centre-lift configuration. To the southwest, the blast was confined by blasted muck. The remainder of the blast perimeter was confined by unblasted rock.
Two BMMs were installed in each hole. As the bench height was 10 m, the target installation depths were 3 m and 6 m below the collar of the hole. The powder factor used for the blast was 0.29 kg/t.
Blast movement calculations
(based on SED and UAV data)
An SED and the new UAV-mounted detector were used to survey the muck pile for BMMs. Due to operational constrains, the UAV-mounted detector attempted to find eight BMMs only. It successfully detected six of them.
Twelve BMMs were installed in seven separate monitoring holes in Blast 2, and all 12 BMMs were detected post-blast. Figure 2 shows a plan view of the blast, including the initiation point, timing contours, and centreline. The numeric labels on the plan correspond with the BMM number. The blast was initiated in a v-configuration from the western edge of the perimeter toward a choked face. The remainder of the blast perimeter was confined by unblasted rock. The powder factor for Blast 2 was 0.27 kg/t.
Blast movement calculations
(based on SED and UAV data)
A SED and the new UAV-mounted detector were used to survey the muck pile for BMMs. Due to operational constrains, the UAV-mounted detector attempted to find five BMMs only. It successfully detected all five of them.
Potential value generated by accounting for blast movement with flight enabled detector
For the purposes of this analysis:
- ore loss is defined as ore sent to a waste dump
- dilution is defined as waste, processed or stockpiled as ore
- misclassification is defined as material with ore classification being treated as ore with a different classification. It is assumed that each delineated polygon has a different downstream destination.
It is important to note that the comparison is made between mining ore blocks in their pre-blast position (ie no blast movement translation and no field adjustments) versus the translated blocks by movement vectors.
The results of the analysis is shown in Figure 3. If the ore was mined in situ, rather than the post-blast locations translated using measured vectors, then there would have been approximately 31 142 tonnes of material sent to the wrong downstream destination (12 per cent misclassification).
The current trend on mine sites across the globe is to increase safety and productivity via use of automation. BMTs ‘off-the-muck-pile’, UAV-mounted BMM detection solution is in line with that trend. There are several key benefits to this approach. On one hand, the UAV-mounted detector system improves safety on treacherous muck piles, while on the other hand it addresses staffing issues at mine sites. An automated detection system also reduces error in measurements by eliminating any human error during BMM detection using BMT’s existing hand-held detector.
The automated detection system will allow mine sites the opportunity to collect BMM data during the stand-off period. This will have significant improvements to reconciliation, reducing misclassification and reducing ore loss and dilution. Therefore, it can be summarised that BMT’s UAV-mounted detector system will allow quicker, faster and easier measurement of BMM data and thereby increase safety and productivity at mine sites where this system is implemented.