The Survey of Sub-Level Caving in Underground Mines Using Geodetic Surveying Methods

Deep beneath the earth's surface, where sunlight never reaches and the air can be thick with dust or dangerous gases, miners face a constant challenge: knowing exactly what the ground looks like around them. To dig safely and efficiently, they must map the tunnels, the open chambers where rock has been removed, and the unstable walls that could collapse. For decades, this mapping relied on surveyors walking into these dark, hazardous spaces with instruments that measured one single point at a time. While this method worked, it was slow, left large gaps in the picture, and forced human workers to stand in areas where a fall or a rockslide could be fatal. In recent years, technology has offered a new way forward, replacing the slow, point-by-point approach with tools that can capture millions of points in seconds, creating a complete, three-dimensional picture of the underground world without requiring a human to stand right next to the danger.

A team of researchers at Fırat University in Turkey set out to test how well these modern tools work in a real, active mine. They focused on a specific type of mining called sublevel caving, a method where the rock is allowed to break and fall into a large, empty space below. This process creates a chaotic, shifting landscape that is incredibly difficult to measure with traditional tools. The study took place in an underground chrome mine near Elazığ, a site where the mine operators had already developed several levels of tunnels. The researchers wanted to see if they could map a dangerous, collapsing section of the mine using three different methods: the old-fashioned way with a total station, a handheld laser scanner that a person carries, and a small drone that flies inside the tunnel. Their goal was not just to see if the new machines worked, but to compare them side-by-side to understand which one provided the best data and, more importantly, which one kept the workers safest.

The team began by establishing a network of reference points, essentially creating a fixed grid of coordinates that would allow them to translate their measurements into a standard map. Using a conventional total station, a device that looks like a high-tech theodolite and uses a laser to measure distances and angles, they mapped the tunnel walls. This process required a surveyor to stand in the tunnel, set up the instrument, and measure specific points on the rock face. Because the tunnel was tall and the floor was uneven, they had to mount the points on the side walls and use a mathematical technique called resection to figure out exactly where the instrument was standing. This method, while reliable, is time-consuming and requires the surveyor to be physically present in the area being measured.

Next, the researchers brought in a handheld laser scanner, a device that looks like a small backpack with a sensor on top. A surveyor walked through the tunnel carrying this unit, which shoots out thousands of laser beams every second to build a detailed 3D model of the surroundings. To get a better view of the caving area, which was partially hidden from the tunnel floor, the operator attached an extension pole to the scanner, pushing it out toward the dangerous zone. This allowed them to capture data from a safer distance than the total station, but they still had to walk right up to the edge of the unstable ground. The device took about four minutes to scan the area, capturing a dense cloud of points that could be turned into a digital map.

The third and most distinct approach involved an underground drone. This was not a toy, but a specialized, rugged aircraft designed to fly in the tight, dark, and often oxygen-poor environment of a mine. The drone was equipped with its own laser scanner and collision sensors that would stop it from hitting the walls. The operator stood safely far away from the caving zone, controlling the drone through a radio link while watching a live video feed on a screen. Once the drone was deployed into the caving area, direct visual contact was lost; however, the operator maintained full control by monitoring the drone's position in real time via the display screen. The drone flew into the unstable area, a place no human would ever dare to enter, and collected data for about seven minutes. Because the drone could fly freely in three dimensions, it did not need an extension pole and could see around corners and into deep crevices that the handheld scanner missed.

When the researchers compared the results, the differences became clear. The handheld scanner was quick and easy to use, but it left significant gaps in the data. Because the operator had to stand on the ground and look up or out, large portions of the caving area remained in shadow, invisible to the laser beams. The drone, however, captured a complete picture. It gathered over three million data points, covering nearly the entire volume of the collapsed rock, whereas the handheld scanner, even with its pole, only managed to see about seventy percent of the area. The drone's ability to fly into the void meant it could reconstruct the true shape of the caving with a level of detail that the other methods simply could not match.

There were trade-offs, of course. The drone system was more complex to set up and required a skilled pilot to operate. There was also a risk that the drone could crash, which would mean losing expensive equipment. The handheld scanner was simpler and the data it produced was slightly more accurate in terms of its position relative to the mine's map, but it could not see everything. The traditional total station, while the most accurate in terms of coordinate transformation, was the slowest and the most dangerous for the human operator, as it required them to stand closest to the hazard.

The study concluded that while all three methods have their place, the choice depends on what the miners need to do. If the goal is to get a quick, rough idea of the space, the handheld scanner is a good tool. But if the priority is to understand the full, complex geometry of a dangerous collapse to plan safe mining operations, the drone is superior. By flying into the danger zone while the operator remained at a safe distance, the drone eliminated the need for a human to stand there, offering a massive improvement in safety. The researchers found that the data collected by the drone allowed them to calculate the exact volume of the empty space, which is crucial for figuring out how much material is needed to fill it back in safely. This precise information helps engineers design better drilling plans and prevents ore from being lost or the mine from becoming unstable. Ultimately, the study showed that these new technologies are not just faster; they are changing the way mines are managed by putting the safety of the workers first while providing a clearer, more complete picture of the underground world.