THE US army is building a bomb that burrows through solid rock and then explodes underground. The project shows that despite having abandoned plans to develop nuclear 鈥渂unker busters鈥� last year, the military is still searching for ways to reach targets such as buried weapons stores.
Known as Deep Digger, the weapon fires volleys of charges from seven cannons to dig downwards. These projectiles penetrate the rock and break it up before exploding with enough force to throw the shattered rock fragments clear, leaving a path for the next round of projectiles.
This mechanism allows the bomb to penetrate rock much more quickly than traditional tunnelling techniques, which rely on drilling a hole, inserting an explosive charge and then laboriously removing the debris ready for the next.
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Deep Digger uses charges with combustible cartridge cases, which burn up rather than adding to the debris. In a demonstration last year, Deep Digger tunnelled through 10 metres of limestone. This compares well with the biggest conventional 鈥渂unker-busting鈥� bomb, the 2000-kilogram GBU-28, which can only force its way through 7 metres of concrete of comparable hardness. Project manager David Burns would not comment on whether the burrowing bomb might be able to go deeper than 10 metres.
Although the bomb can pierce stone and concrete, it finds sand difficult, because holes tend to be refilled as soon as the digger has created them. 鈥淭here are still engineering challenges in dealing with soft materials,鈥� Burns says.
The initial research was sponsored by the Defense Threat Reduction Agency, part of the US Department of Defense, which is investigating ways to destroy chemical and biological weapons stored in deep bunkers. An 18-month project is now under way to produce an operational prototype. The US army鈥檚 Armament Research, Development and Engineering Center (ARDEC) at Picatinny, New Jersey, is building the burrowing unit, which will be integrated with the warhead and guidance and parachute systems to create the complete Deep Digger device.
The technology could find other uses. As a wall-breaching device that cuts entry holes in buildings from a short distance away, it could eliminate the need for soldiers to put explosives in place by hand. And it could also have a use in mining and quarrying. A larger version of the technology that used non-explosive projectiles could break up ore faster and more cheaply than existing methods.
