# How to destroy an underground tunnel ? **URL:** \ **Category:** Factual Questions\ **Created:** [July 26, 2014, 2:06pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096 "2014-07-26T14:06:47Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Bozuit](https://avatars.discourse-cdn.com/v4/letter/b/edb3f5/32.png) [@Bozuit](https://boards.straightdope.com/u/Bozuit)\ **Post date:** [July 26, 2014, 5:55pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/21 "2014-07-26T17:55:32Z")
> [@EdwinAmi](#): > > What? Come on, you think boards in a small tunnel stuck right up against the dirt will ever burn through significantly? No surface area for the fire to burn on, let alone let oxygen in. And here’s an added confounder, burnt/carbonated wood is actually stronger than the original wood (well, burnt to a certain degree only, and of course it loses its tensile strength. Plus, this is just something my Dad told me (we’re builders) ) There’s a medieval siege technique called sapping which involved digging tunnels under fortifications and then burning the supports, causing the walls to collapse. Of course, those supports were built to be burnt, but there’s certainly a precedent. The shoring could be replaced with more combustible materials. Also, substances like thermite contain their own oxygen supply and would burn quite happily down there, even if the intended occupants/users of the tunnels didn’t need oxygen themselves. ETA: > [@EdwinAmi](#): > > Is it? You could pump sulfur hexafluoride or similar heavier-than-air gases, and it would push out the air, making the tunnel impassible (you’d asphyxiate). And indeed with something as heavy as sulfur hexafluoride, that set-up would be pretty stable (winds would push out some of the gas at the ends, whenever there would be said winds, but this could be replaced by pumping more gas later. And indeed, I do believe the gas would be cheaper than concrete > It’s an interesting proposal Until Hamas get their hands on some fans/oxygen masks. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 26, 2014, 5:56pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/22 "2014-07-26T17:56:06Z")
Any gas, even sulfur hexafluoride, will diffuse out way too quickly to be practical. You’d be much better off flooding them with water, which would be both more effective for longer times and cheaper. Ultimately, though, if you care about what’s on the surface, then filling them with concrete is the only solution that doesn’t need constant maintenance. If you don’t care about the surface, then it’s either that or collapsing them (probably using potent explosives). ---
**Author:** ![EdwinAmi](https://avatars.discourse-cdn.com/v4/letter/e/5fc32e/32.png) [@EdwinAmi](https://boards.straightdope.com/u/EdwinAmi)\ **Post date:** [July 26, 2014, 6:06pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/23 "2014-07-26T18:06:08Z")
> [@](#): > > if you care about what’s on the surface, then filling them with concrete is the only solution Until the heavy concrete starts settling and above-ground you’ve inadvertently started creating a ditch 😛 ---
**Author:** ![EdwinAmi](https://avatars.discourse-cdn.com/v4/letter/e/5fc32e/32.png) [@EdwinAmi](https://boards.straightdope.com/u/EdwinAmi)\ **Post date:** [July 26, 2014, 6:10pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/24 "2014-07-26T18:10:03Z")
> [@](#): > > Any gas, even sulfur hexafluoride, will diffuse out way too quickly to be practical. You’re underestimating how heavy sulfur hexafluoride is [https://www.youtube.com/watch?v=XjCmwuGKR6g](https://www.youtube.com/watch?v=XjCmwuGKR6g) I think the part where you can “float” a boat on it, and then “pour” the gas in to cause it to sink is a compelling demonstration. This stuff will NOT diffuse normally like most other gases, it’ll just sit there. Winds will cause some of it to blow away at the ends. Note, only at the ends, the friction in a long tunnel limits through-drafts that can be formed by non-directed winds. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 26, 2014, 6:38pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/25 "2014-07-26T18:38:02Z")
> [@](#): > > You’re underestimating how heavy sulfur hexafluoride is I am not. You’re underestimating the fact that sulfur hexafluoride is a gas. It will diffuse according to the exact same laws as any other gas. Those laws depend on the molecular mass of the gas, and since SF[sub]6[/sub] is very heavy, it will therefore diffuse slowly enough to enable the foil-boat demonstration. But give it an hour or so, and it’ll be distributed almost perfectly uniformly throughout the room, not confined to that aquarium. Did you notice how the kids in your video had a cover over the top of the containers when not using them? That’s why. Besides which, even if SF[sub]6[/sub] _would_ work, what’s the advantage of using it instead of water? ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [July 26, 2014, 6:39pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/26 "2014-07-26T18:39:38Z")
Hmm, be contrary, distribute flint gravel along the floor, pump them full of oxygen. I always thought it would be a good idea to keep filling them with seawater, but adding human was would be a bonus. Run a pipeline all along the border, keep filling the tunnels. If you’re lucky, depending on ground conditions, that would add complications to undiscovered or future tunnels. ---
**Author:** ![EdwinAmi](https://avatars.discourse-cdn.com/v4/letter/e/5fc32e/32.png) [@EdwinAmi](https://boards.straightdope.com/u/EdwinAmi)\ **Post date:** [July 26, 2014, 7:10pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/27 "2014-07-26T19:10:38Z")
> [@](#): > > It will diffuse according to the exact same laws as any other gas. Gases (fluids in general) can fail to diffuse if they’re at the bottom of a lighter gas There are parts of sea abysses and caves that have a saltier layer on the bottom because the saliter layer i heavier than the above water, that remains that way for thousands of years. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [July 26, 2014, 7:40pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/28 "2014-07-26T19:40:32Z")
Filling the entire length of a tunnel with concrete would be very difficult and expensive. Why not just fill the tunnel with water (or SF6 if you want to be exotic) and then just seal the ends of the tunnels (for some reasonable distance into the tunnel) with concrete? Then, monitor the known portals on some schedule to prevent them from being re-opened; and otherwise, just keep pumping water (or gas) into the tunnels to keep them full. Or nuke them all from outer space. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [July 26, 2014, 7:43pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/29 "2014-07-26T19:43:04Z")
Here’s what I wonder: If it’s all _that_ difficult and resource-intensive to destroy all those tunnels, then how difficult and time-consuming and resource-intensive was it to build them all in the first place? Intuitively, at least, one would suppose that it’s much more difficult to build those tunnels than to destroy them. There’s some room for the fighting of some iggorance here! ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [July 26, 2014, 7:48pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/30 "2014-07-26T19:48:16Z")
> [@Senegoid](#): > > Here’s what I wonder: If it’s all _that_ difficult and resource-intensive to destroy all those tunnels, then how difficult and time-consuming and resource-intensive was it to build them all in the first place? > > Intuitively, at least, one would suppose that it’s much more difficult to build those tunnels than to destroy them. > > There’s some room for the fighting of some iggorance here! On the one side is very cheap labour; on the other, expensive labour, expensive materials, etc. I still think the simplest solution is to get one of those tunnelling machines they use to build subways and giant water supply tunnels. Run it along the border at the right depth. Behind it, block off the tunnel at intervals and keep it filled with (sea)water. Monitor depth. If the water drops suddenly, someone broke through. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [July 26, 2014, 8:06pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/31 "2014-07-26T20:06:46Z")
A lot depends on the soil above and around the tunnel. If it is loose-ish, easily crumbled stuff (packed dirt, broken rock, shale, etc.), then you just blow it up. The stuff breaks up and falls in. Not necessarily all the way in from the surface. There will be air pockets (after all, the falling crap has to come from some place), but they would be small and spread all over. The idea is that trying to redig the tunnel is not going to work. The “ceiling” zone is now too weak and will easily cave in during re-excavation. The force of the explosions should have created many fractures in the ground that just makes things too costly to redig in the same location. The diggers would just move over a hundred meters and start over. If it’s pretty solid rock, then the explosions aren’t going to damage the surrounding rock enough to prevent determined diggers from trying to clear out the rubble. The air pockets will be bigger, etc. OTOH, this may not be the sort of ground the diggers would be trying to bore through in the first place. Keep in mind, that a tunnel location, once found, is pretty much useless. One thing the Israelis could do is blow it up a bit. Let the Palestinians redig it. Blow it up again. (Maybe while the diggers are still at it.) Finding the tunnels is the biggest challenge for the Israelis. I’d call in Goto Dengo. He knows how to blow up tunnels to discourage redigging. ---
**Author:** ![GaryM](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/garym/32/241_2.png) [@GaryM](https://boards.straightdope.com/u/GaryM)\ **Post date:** [July 26, 2014, 8:11pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/32 "2014-07-26T20:11:00Z")
> [@jnglmassiv](#): > > I thought those were more to destroy the tunneling equipment. Well, that might help end tunneling efforts, but it’s not what I intended. ---
**Author:** ![GaryM](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/garym/32/241_2.png) [@GaryM](https://boards.straightdope.com/u/GaryM)\ **Post date:** [July 26, 2014, 8:13pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/33 "2014-07-26T20:13:26Z")
> [@EdwinAmi](#): > > From what I understand, that doesn’t destroy the tunnels, just the rodents/critters. Why would it destroy the tunnel? There is a “blast” but it isn’t significant enough to destroy tunnels in solid dirt, it’s only some light flammable gas, hardly a bomb set up or dynamite. If you look at the videos on their website it appears that at least some of the tunnels are destroyed. But I admit that they aren’t very deep. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 26, 2014, 9:53pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/34 "2014-07-26T21:53:31Z")
> [@](#): > > Quoth **EdwinAmi** : > > Gases (fluids in general) can fail to diffuse if they’re at the bottom of a lighter gas And just what is it that’s stopping them? Air makes a really lousy barrier. ---
**Author:** ![EdwinAmi](https://avatars.discourse-cdn.com/v4/letter/e/5fc32e/32.png) [@EdwinAmi](https://boards.straightdope.com/u/EdwinAmi)\ **Post date:** [July 26, 2014, 10:11pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/35 "2014-07-26T22:11:29Z")
> [@](#): > > And just what is it that’s stopping them? Air makes a really lousy barrier. the weight of the air above it, providing some pressure brah, look, you’re wrong. Like I said there are numerous aquatic phenomena where this happens and remains stable for thousands of years. Saltier water staying on bottom, saltier water staying below freshwater. _this actually happens on a regular basis and remains stable_ ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [July 26, 2014, 10:44pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/36 "2014-07-26T22:44:37Z")
Lets not over think this. Empty three bags of rattlesnakes throughout the tunnel. Add ten bags of rats for a sustainable food source. Partially close each end with loose rock. Problem solved. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 26, 2014, 10:45pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/37 "2014-07-26T22:45:42Z")
Where does it happen and remain stable that one layer of gas is trapped under another layer of gas? ---
**Author:** ![ToughLife](https://avatars.discourse-cdn.com/v4/letter/t/8797f3/32.png) [@ToughLife](https://boards.straightdope.com/u/ToughLife)\ **Post date:** [July 26, 2014, 10:59pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/38 "2014-07-26T22:59:32Z")
There has been a lot of interesting ideas so far. It’s clear to me now that destroying a tunnel is a very difficult, time consuming and expensive task. Apparently when Israel claims that some tunnel has been destroyed it generally means only entrances and may be some immediate surroundings were destroyed . They are probably monitoring those locations which is good enough to prevent rebuilding attempts . And so it goes …cat and mouse … ---
**Author:** ![EdwinAmi](https://avatars.discourse-cdn.com/v4/letter/e/5fc32e/32.png) [@EdwinAmi](https://boards.straightdope.com/u/EdwinAmi)\ **Post date:** [July 26, 2014, 11:10pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/39 "2014-07-26T23:10:22Z")
> [@](#): > > Where does it happen and remain stable that one layer of gas is trapped under another layer of gas? It’s all fluid mechanics, and I gave you undeniable evidence of water/liquid pheonmena Though I do vaguely remember something about gasses in caves getting trapped in the bottom layer Nobody’s saying it’s super stable, like I said, wind will \*\*eventually \*\*blow it all away. Maybe a month? I have no freggin idea how windy it is in israel ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [July 26, 2014, 11:12pm UTC](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096/40 "2014-07-26T23:12:28Z")
They buried anti personnel mines in WWI to prevent tunneling. Both sides would spend months tunneling under an enemy trench or operations post. Set explosives and ignite. Blowing everyone in that trench apart. Burying mines deep works quite well when hit by a shovel. If nothing else it slows down the tunnelers because they never knew when their shovel might hit a mine. [Previous page](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096.md?page=1) [Next page](https://boards.straightdope.com/t/how-to-destroy-an-underground-tunnel/694096.md?page=3)