In a first for the world, the “Gangtie Jiliang” or “steel backbone” boring machine is designed to delve straight down to a depth of one kilometer through the earth’s crust. Weighing about 500 tons and measuring 8.1 meters wide, the machine looks less like mining equipment and more like an “underground aircraft carrier”. Developed by the China Railway Construction Corporation (CRCC), the machine has been deployed in an iron ore project in Liaoning province. Its mission is to unlock a hidden world of wealth buried beneath the earth’s crust. China’s deep mineral deposits are vast. Experts estimate there is twice as much mineral wealth deep underground than what has already been proved near the surface. A 2018 estimate by the China Geological Survey said antimony resources located up to 2,000 meters deep are 5.3 times larger than known reserves. The metalloid is critical for batteries, semiconductors and metal alloys. For lead, zinc and gold, the deep-underground resources are roughly four times larger. Tungsten deposits located deep underground are about three times larger than those found near the surface. The same three-to-one ratio of deep-to-shallow resources applies to lithium, rare earths and coal.
Miners have scraped at the earth’s surface for these minerals for centuries, but the easy pickings are gone. Unlike other methods for sinking deep shafts, Gangtie Jiliang is built specifically to tackle hard rock. It has a massive circular cutter head that covers the full diameter of the shaft, drilling vertically from the surface like an oversized electric drill. One of the most persistent challenges was how to efficiently remove enormous quantities of broken rock and muck. Unlike a horizontal tunnel-boring machine, a vertical shaft borer must contend with gravity, which causes debris to accumulate directly in front of the cutter head. For nearly six months, the team tried out various solutions without success. The breakthrough finally came during a walk in a wetland park in Changsha, encountering a dragon-bone waterwheel. Inspired by the ingenious wooden irrigation device used in China more than 2,000 years ago, engineers developed an intelligent, vertical muck-removal system based on a similar structure. Its hourly transport capacity is equivalent to 10 trucks working simultaneously.
Excavating a kilometer underground often involves extreme ground stress and high water pressure. Without immediate support, rock walls can deform or collapse as soon as they are cut, a phenomenon known as the “safety curse” of deep construction. Following joint research with several domestic scientific institutions, the team developed a way to reinforce the shaft walls in real time. Ding said the team intended to apply the Gangtie Jiliang to a wider range of tasks in the future, helping China “seize the technological high ground” in the development of deep-underground excavation. Several leading Chinese researchers pointed out that as China’s shallow mineral resources were depleted, the industry had to tap into resources at depths exceeding 1,000 meters to sustain growth, the South China Morning Post reports.
