Tunnelling method a legacy of the Cold War

It’s hard to believe there could be a connection between intercontinental ballistic missiles and hard-rock mining. But there is.

The Cold War era saw an unprecedented amount of effort and hard cash directed toward the sciences and new technologies. Rock breaking was one of them.

It all came about in the well-publicized plan of the U.S. military to conceal its latest MX missiles from prying Soviet satellites. It was well publicized because any one of the proposed schemes, and there were several, would have cost billions of dollars.

One of the schemes entailed driving a series of underground tunnels with the intention of drilling the missile chambers up to surface as soon as a nuclear attack began. The Soviets would not be able to target the missile sites because they wouldn’t know where they were until it was too late. Miles of tunnels would be needed for the strategy to work and high-speed tunnelling was essential. However, orthodox drill-and-blast methods were too slow and would pose insuperable ventilation problems.

In addition, the military couldn’t give the Soviets a massive generating plant to target, so the tunnelling method would not have to make heavy demands on the power supply. (The power station would be underground but the abundance of waste heat would easily be detectable to heat sensors.) One of four companies asked to develop a new tunnelling method was Machine Design Engineers of Seattle, Wash.

“Work stopped on the project when funding came to an end three years ago,” Dennis Martin, company president, said. “Otherwise, it is very likely we would have a commercial system by now.”

The system was successfully field-tested and all that remains is to fine-tune the explosive’s chemistry and resolve final machine design.

The Seattle company’s continuous-mining concept involved “miniaturized blasting.” There are a number of continuous miners on the market today. They are the road headers used by many European coal mines, and function by chewing away the tunnel face by means of mechanical cutters. While they can do this efficiently, the machines themselves are leviathans. They weigh 30-100 tons and upwards, they are heavy power consumers and it is a tortuous process moving them from one place to another.

Explosives, on the other hand, are convenient-size packages of condensed energy. The problem is to control the energy, and miniaturized blasting is one of the solutions.

Only small quantities of explosives are detonated at a time. The drill holes are three feet long but only three-eighths of an inch in diameter. There is just sufficient explosive to break the rock and move it a few feet from the tunnel face. There is little concussion, practically no fly rock and the equipment remains at the face continuing drilling, loading, blasting and moving out the broken rock without pause. Commercial machines will be remote-controlled.

“The major hurdle was finding the proper explosive,” Martin said. “It had to have sufficient power, be detonated by percussion without being too sensitive to shock and generate the least volume of noxious gases.”

A proprietary explosive was ultimately formulated from compounds developed by rocket-fuel scientists. Theoretically, it produces only water vapor and nitrogen gas when detonated and the company believes little more test work is needed to optimize the explosive’s chemistry.

The company has named its method the Automated Drill and Blast System. It carried out field testing at a basalt quarry near Seattle which hosts a hard and extremely tough crystalline dyke rock.

Drilling, explosive loading apparatus and detonating equipment, all automatically sequenced, were fitted on to a mobile carrier. A tunnel 15 ft. long, 10 ft. wide and 9 ft. high was driven into the quarry face. All the major goals of the research program were accomplished. Then, work stopped; there was no more financing.

But other companies are in the field. One of the most vigorous has just completed underground trials at the Mount Isa mine in Australia. The company is Sunburst Excavation of Denver. According to Edward Michalik, president, Sunburst’s technology has aroused considerable interest. “There is the strong possibility the Australians will sponsor further development,” he said. Unlike the Seattle company’s procedure, drill holes are not loaded with explosive. Rather, a gun-like device fires gases from an explosive charge into the drill hole rupturing the enclosing rock. All drilling and blasting are automated. The process of rock breaking is continuous.

A number of other organizations are working in the same field, all with the objective of developing a workable continuous-mining system, the key to propelling mining technology into the 21st century.