# Destroying/Filling in Tunnels **URL:** \ **Category:** Factual Questions\ **Created:** [November 17, 2011, 7:09pm UTC](https://boards.straightdope.com/t/destroying-filling-in-tunnels/603254 "2011-11-17T19:09:35Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![11811](https://avatars.discourse-cdn.com/v4/letter/1/9d8465/32.png) [@11811](https://boards.straightdope.com/u/11811)\ **Post date:** [November 17, 2011, 7:09pm UTC](https://boards.straightdope.com/t/destroying-filling-in-tunnels/603254/1 "2011-11-17T19:09:35Z")
When smuggling tunnels are discovered from Egypt to Gaza or from Mexico to the US, how are they destroyed? [ol] [li]Explosives?[/li][li]Fill in with rubble?[/li][li]Pump in concrete?[/li][/ol] ---
**Author:** ![Al\_Bundy](https://avatars.discourse-cdn.com/v4/letter/a/e79b87/32.png) [@Al\_Bundy](https://boards.straightdope.com/u/Al_Bundy)\ **Post date:** [November 17, 2011, 11:08pm UTC](https://boards.straightdope.com/t/destroying-filling-in-tunnels/603254/2 "2011-11-17T23:08:36Z")
And I don’t have any answers, only more questions. Explosives would cause the ground to sink along the path, possibly damaging structuresl Filling in with rubble would seem to allow easy removal of the rubble along the way, thereby re-establishing the tunnel. A cement pumper could fill the tunnel easily enough. However. The cured cement could be used as a path to redig the tunnel and have one solid wall along the course. All methods seem to have risks. I bet the authorities don’t want to reveal all their techniques for dealing with them either. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [November 17, 2011, 11:14pm UTC](https://boards.straightdope.com/t/destroying-filling-in-tunnels/603254/3 "2011-11-17T23:14:59Z")
Fill it with raw sewage. ---
**Author:** ![Baracus](https://avatars.discourse-cdn.com/v4/letter/b/2bfe46/32.png) [@Baracus](https://boards.straightdope.com/u/Baracus)\ **Post date:** [November 18, 2011, 12:26am UTC](https://boards.straightdope.com/t/destroying-filling-in-tunnels/603254/4 "2011-11-18T00:26:20Z")
ON an episode of “Border Wars” or some similar show they showed a tunnel between the U.S. and Mexico being pumped full of cement. ---
**Author:** ![mac\_bolan00](https://avatars.discourse-cdn.com/v4/letter/m/b3f665/32.png) [@mac\_bolan00](https://boards.straightdope.com/u/mac_bolan00)\ **Post date:** [November 18, 2011, 12:46am UTC](https://boards.straightdope.com/t/destroying-filling-in-tunnels/603254/5 "2011-11-18T00:46:56Z")
collapsing the tunnel is the most efficient. if it’s deep enough with sufficient virgin rock or even loose rock overhead, there shouldn’t be much problem at the surface. the general rule is, on a cross section of the tunnel and the ground surface, draw 45-degree lines from the tunnel sides upwards to the surface. if it’s loose rock all the way to the surface, the ground will subside within that inverted triangle by the tunnel height multiplied by the ratio of the tunnel’s surface on cross section with the surface of the triangle. so the deeper it is, the less noticible subsidence you have. if it’s virgin rock, you need to blast only two-thirds of the tunnel’s total volume from the rocks overhead since blasted rock has twice the volume of in-situ rock. after collapsing, the next best thing is slurry filling with cement (although sand already works well, provided both ends are sealed.) filling with rubble is the least efficient because of the time and cost to haul the rubble, and the difficulty of filling a cavity up to the ceiling. imagine hundreds of wheelbarrows to fill a long tunnel. ---
**Author:** ![Geek\_Mecha](https://avatars.discourse-cdn.com/v4/letter/g/ecae2f/32.png) [@Geek\_Mecha](https://boards.straightdope.com/u/Geek_Mecha)\ **Post date:** [November 18, 2011, 3:11am UTC](https://boards.straightdope.com/t/destroying-filling-in-tunnels/603254/6 "2011-11-18T03:11:38Z")
> [@Baracus](#): > > ON an episode of “Border Wars” or some similar show they showed a tunnel between the U.S. and Mexico being pumped full of cement. Saw this on either Border Wars or one of the drug documentaries on Nat Geo. They fill it with cement. ---
**Author:** ![Rhythmdvl](https://avatars.discourse-cdn.com/v4/letter/r/85f322/32.png) [@Rhythmdvl](https://boards.straightdope.com/u/Rhythmdvl)\ **Post date:** [November 18, 2011, 3:47am UTC](https://boards.straightdope.com/t/destroying-filling-in-tunnels/603254/7 "2011-11-18T03:47:21Z")
Shelter for homeless C.H.U.D.s. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [November 18, 2011, 1:35pm UTC](https://boards.straightdope.com/t/destroying-filling-in-tunnels/603254/8 "2011-11-18T13:35:06Z")
> [@Fear\_Itself](#): > > Fill it with raw sewage. This (according to Paul Brickhill) is what the German prisoner of war camp officers did at Stalag Luft III when they discovered the incredibly long and deep and well-shored tunnel that almost made it past the wire (The one they discovered in “The Great Escape”). They used to use explosives to collapse them, but this one was too well-built, and by filling it with sewage they guaranteed that, even if the prisoners were willing to go and dig it out again, they couldn’t do so undetected. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [November 18, 2011, 2:28pm UTC](https://boards.straightdope.com/t/destroying-filling-in-tunnels/603254/9 "2011-11-18T14:28:34Z")
Great. Me and Nazis think alike. ---
**Author:** ![Rhythmdvl](https://avatars.discourse-cdn.com/v4/letter/r/85f322/32.png) [@Rhythmdvl](https://boards.straightdope.com/u/Rhythmdvl)\ **Post date:** [November 18, 2011, 2:42pm UTC](https://boards.straightdope.com/t/destroying-filling-in-tunnels/603254/10 "2011-11-18T14:42:53Z")
You know who else thought like Nazis?