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The shock waves from ground-penetrating nuclear strikes may not behave as previously believed, rendering the design of underground nuclear bunkers and military facilities vulnerable, say Chinese researchers. Photo: Shutterstock Images

Chinese tests show nuclear bunkers are not what they used to be, with earth-penetrating weapons on the rise

  • Current engineering standards ‘severely underestimated the actual impact’ of a nuclear blast targeting underground defence facilities, according to paper
  • Major nuclear powers have a growing interest in small-yield bunker busters because they produce little or no radioactive fallout to pollute the landscape
Science

China has built a new research facility to simulate an attack by nuclear bunker-busting weapons and learn how they damage defence facilities, even those built at extreme depths, according to military scientists involved in the project.

In the past, shelters buried several hundred metres deep were rated nuclear-proof but the Chinese test facility shows that a tunnel more than 2km (1.24 miles) under the surface could be destroyed, according to the researchers.

In one test, the simulated tunnel almost crumbled after taking hits the effective equivalent of five consecutive strikes by earth-penetrating nuclear weapons, an outcome that would have once been considered impossible.

The Cheyenne Mountain Complex at Peterson Air Force Base in Colorado Springs, Colorado. Photo: norad.mil

For instance, the Cheyenne Mountain Complex, home to the North American Aerospace Defence Command, was dubbed by the US military as the “most secure facility in the world” because it was protected by granite above more than 500 metres (1,600 feet) thick.

The Russian government’s doomsday shelter was buried 300 metres deep in the Ural Mountains. West of Beijing, China’s Joint Battle Command Centre, for extra precaution, was built in natural karst caves about 2km underground.

Openly available information suggests most ground-penetrating weapons could not reach a depth beyond 40 metres (130 feet).

But with the recent rapid development of technology, existing safety standards may be outdated and have “severely underestimated the actual impact” of nuclear weapons, said Li Jie, lead project scientist with the Army Engineering University of PLA in Nanjing, Jiangsu province, in a paper published in the peer-reviewed Chinese Journal of Rock Mechanics and Engineering last week.

According to some calculations by Chinese researchers based on underground nuclear testing data and computer simulation, the destruction caused by a nuclear bunker buster using the latest technology could reach three to 10 times deeper underground than previously thought.

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If carefully planned, a tactical nuclear warhead could trigger seismic activity which would release total energy up to 1,000 times that produced by the weapon itself, causing irreparable damage to infrastructure far from the detonation site, Li and his colleagues said.

Major nuclear powers have a growing interest in small-yield bunker busters because these weapons produce little or no radioactive fallout to pollute the environment.

The latest model of the US B61 nuclear bomb, under development since 2019, has a yield ranging from 0.3 to 50 kilotons – just a fraction of the power of conventional nuclear weapons, according to the Federation of American Scientists in Washington.

These relatively “clean” nuclear weapons can be delivered by hypersonic missile to evade missile defence systems and hit the same strategic target – such as government and military headquarters far behind battle lines – multiple times.

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Replicating a nuclear bunker-busting process in a laboratory has several challenges, according to Li.

The shock waves produced by a nuclear explosion were not only powerful but their shapes changed as the waves went through the ground, the team said, adding that a suitable simulating platform required the right waves to arrive at the right place at the right time – a difficult achievement.

Li and his colleagues found that a tunnel buried 2km deep would be squeezed by the rocks around it with the average stress reaching more than 600kg (1,300lbs) per square centimetre (0.2 square inches).

In the scale model testing facility, sample blocks of various rock types were put into a machine applying pressure from all sides, with high-strength liquid-filled capsules placed between the plates and rock samples.

The rocks were pressed over a long period until the structure stabilised before a tunnel could be bored slowly into the rocks to create a bunker.

A heavy metal bullet would be fired at the rocks from above, simulating the blast of a nuclear warhead with a yield up to 200 kilotons.

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The results of some initial experiments at the facility suggested that a popular theory used to design most nuclear-proof bunkers around the world could be wrong, according to Li’s team.

The theory assumed the Earth’s crust was, more or less, one piece and that the shocks from a nuclear blast travelled in the ground like waves in water, losing energy as their distance increased.

But the test results showed that the shock waves could “jump” from one location to another, ultimately passing the destructive energy farther than previously thought possible.

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Data from the experiments could lead to a more accurate mathematical model to predict how severely an underground facility would be damaged under multiple nuclear strikes and what measures could be taken to reduce the destruction, according to the researchers.

China has maintained a nuclear stockpile smaller than those in the United States and Russia and Beijing has said that it would not use a nuclear weapon unless China came under attack.

But to retaliate, its nuclear forces would need to survive the first wave of attack.

In January, five permanent members of the United Nations Security Council issued a rare joint statement declaring that “a nuclear war cannot be won and must never be fought” and must be avoided to the best of their ability.
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