Friday, November 3, 2023

Tunnels, spalling and liquefaction

Back when I was a sproutling engineer, it was possible to go to the library in the Engineering building and pull interesting books off the shelf and give yourself an education outside of the official curriculum.

For instance, there are some phenomena that seem to fall in the cracks between Civil, Mining and Mechanical engineering.

Photo credit


The mechanism whereby rock faces are turned into gravel is that the explosive material creates an intense sound-wave through the media as illustrated in the second image. The velocity of the rock face creates tension in the rock which exceeds the tensile strength of the rock. Fractures propagate along pre-existing cracks.

More intense explosives impart higher-frequency pulses which result in smaller gravel. Lower intensity (i.e. slower) explosives like blackpowder produce boulders and slabs.

Spalling is one of the mechanisms for defeating armor in tanks. A HE round does not need to breach the armor if it can detach projectiles from the inside surface to bounce around and puree the passengers. Heavy fabric is draped inside of the armor to contain spalling and that fabric is appropriately named "spalling curtains".

Why this might be important

Tunnels can be destroyed via spalling and the attendant liquification of the earth

If you look back at the second image you will see dense areas that are under compression and less dense areas that are in tension.

Dried earth and poor quality rock are held together by friction or weakly bonded by dried carbonates and other salts. The weight of the overburden causes friction between the particles which holds them in place.

A shock-wave that is traveling horizontally first makes a tunnel wider as the side-wall closest to the explosion spalls into the vacant space (and simultaneously knocks away vertical shoring material. Then the shock-wave liquifies the earth the (now larger) upper span as the tensile portions of the wave pass by.

Remember the Cold War?

A great deal of effort and science went into figuring out how to destroy weapons that were buried in silos.

A silo is merely a vertical tunnel.

Bombs were developed that could be dropped from height and they were designed to not detonate with the initial shock of impact but to penetrate reinforced concrete and detonate at a predetermined depth.

Shaping the HE in the bomb in a long, cylindrical form created a shaped charge that caused most of the energy to radiate radially, parallel to the ground with the expectation that spalling and liquefaction would neutralize the silo and the contents therein.

Exotic tactics create exotic vulnerabilities

Hamas is on record as saying that there are no civilians in the tunnels. That makes them pure military targets.

Tunnels have vulnerabilities.

We are starting to see massive protests. As normal people, we see the threat they present to us BUT massive numbers of highly emotional people who are tightly packed together have their own vulnerabilities. There are reasons that professional military do not fight this way any more.

Can you imagine the effect of a cheap fog machine and a couple of Dollar General dummies popping up wearing "Chemical Warfare" gear.

Or consider some  fireworks enthusiast launching some loud, star-burst rounds overhead.

You can't shout "FIRE!!!" in a crowded theater for a reason. The stampede kills.

Does anybody doubt that there are elements of Hamas who would NOT launch rockets at their own supporters in the US as a false-flag to stop aid to Israel?

Don't be stupid. Stay away from crowds. And don't expect a tunnel to save you.


  1. I learned some things. Thanks.--ken

  2. I’m not remotely an engineer, but my feeble memory recalls that word being “liquefaction”. Am I wrong, or are the terms interchangeable?

    1. Good catch. Poorh spelhin is allmost a requirmint 4 ingineerin

  3. Hopefully someone is paying attention to how the Israelis manage their Hamas tunnel problem. We may be able to apply their methods to our own border tunnel problems.

  4. Composite and spaced armor constructions in AFVs defeat spalling due to HESH (High Explosive Squash Head) warheads, but HESH warheads are still very useful against concrete revetments.

    The Israelis could also use water or thermobaric devices to defeat the Hamas tunnels. The Mediterranean is not far away from any point in Gaza and really big mining pumps can always pump water into tunnels.

    We invented thermobaric devices during the Vietnam War, but the Russians have really developed the technology to a much higher degree. Russian and Ukrainian references to thermobaric attacks are often mistranslated a "heavy flamethrower" attacks. These devices spew a high volatility liquid or gaseous fuel (specifically a solid oxide former) and then ignite it with a modest explosion. Thermobarics actually create a partial vacuum as all the oxygen is consumed.

  5. Truly I don't have any idea why more individuals haven't attempted this, I work two movements, 2 hours in the day and 2 PM. What's more, I clearly got a check of twelve thousand bucks. What's wonderful is I'm telecommuting so I get additional time with my children..Read this article for more details..

  6. Just pick the shortest guy, give him a flashlight, a 1911 and 2 extra mags.
    Worked in the 70s....


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