How Robots Helped Restore Operations at a Collapsed Mine
Early in the morning of August 13, 2021, Justin Disney, supervisor of the Lhoist limestone mine near Crab Orchard, Tennessee, in North America, heard a sound he had never heard in his 16 years working at the mine.
“It was like rain falling from the pillars. At that moment, I suddenly realized what was happening and began the evacuation. By 6:40 everyone was accounted for, and at about 6:59 and 48 seconds the mine collapsed”
The mine, which is more than 100 years old, released a blast of air, mud and debris moving at about 193 km/h from all portals and ventilation shafts when it collapsed. Thanks to Disney's evacuation, no one was injured during the incident. The event was found to have been caused by the collapse of very old pillars (40 to 70 years old), which led to significant surface subsidence.
The US Mine Safety and Health Administration (MSHA) quickly determined that the surface subsidence area left after the collapse, 244 meters wide and 30 meters deep, was too dangerous for human inspection. However, a robotic solution would not be simple either.
Before the collapse, miners used a two-way radio system that operated through a leaky feeder from PBE Group. The leaky feeder lacked the bandwidth to support drones or robots. Even if it could, it stopped working after the collapse.
“It is a unique challenge to try to create an underground communications system that provides the bandwidth needed for video processing and LiDAR applications without ground infrastructure”
PBE Chief Technology Officer Rob Koch, faced with no network or power after the accident, decided that the best solution would be a low-latency, high-bandwidth wireless IP network. He ultimately chose a Rajant mesh IP network and robots from Australian Droid and Robot (ADR). PBE, Rajant and ADR had previously worked together on solutions.
The team used 10 ADR Explora XL autonomous robots, the Rajant Kinetic Mesh wireless underground communications network, and PBE equipment and technology. The robots placed three network infrastructure points inside the mine, the deepest of which is 1.7 km down, and installed eight robo-hubs.
“We were able to create a really good visualization of where the collapse occurred and of the safe zones where we could send crewed inspections”
ADR robots inspected all the necessary areas of the mine while transmitting video data at speeds of up to 80 Mbit/s. The robots were able to complete the inspection and allow miners to return to the mine to restore power and communications.
“ADR has a small fleet of robots ready for emergency work, but this required more units with different sensors and capabilities. We quickly built more robots and carried out thorough testing to simulate the conditions and distances we would face in the US. We had teams across Brisbane, and at one stage we had robots deployed across several suburbs, controlled from a central hub. The robots were shipped to the US in less than a month, accompanied by André Preller, chief electronics engineer, and Callum McDermid, senior robotics engineer. After daytime tests on the surface, the robots entered the mine, and each robot relayed the communications signal to the next, creating a daisy-chained network with high bandwidth inside the mine. A week later, the team had gathered enough data for the mining crew to resume work — the only company in the world that could help with the right equipment at the right time”
The mine intends to deploy the Kinetic Mesh network throughout its territory. In the future, if they ever face an instability problem, they can simply send one ADR robot into the mine using the existing network infrastructure, protecting worker safety and keeping operations running smoothly.
“When we learned about the need for unmanned inspection after the collapse, we focused on finding the best solution for fast, flexible deployment and high performance. The mine needed a flexible, high-bandwidth data network to support a wide and changing set of inspection deployments. Rajant's mesh technology was the obvious choice for this purpose. During execution, the task was to design network elements that the robots themselves would deploy inside the mine. We quickly moved on to finding the best antenna technology for the robots and transit nodes. We then went to the site to build deployable robot nodes and a ground data network to transmit data to the inspection operations center. The network elements and antennas provided enough time for the inspection. We are glad the mine chose PBE for this pioneering project to safely resume operations using the best available technologies”
