Why Tunnels Don't Collapse

How simple reinforcement is used to prevent collapse of rock tunnels.

Tunnels play an important role in our constructed environment as passageways for mines, conveyance for utilities, and routes for transportation. Rock bolts are a type of reinforcement for stabilizing rock excavations, usually made from steel bars or bolts. This simple construction method dramatically reduces the cost of making tunnels through rock safe from collapse.

Tonic and Energy by Elexive is licensed under a Creative Commons Attribution License

Credit for this demonstration that was originally conceived by Tom Lang

[PracticalEngineeringChannel]

I pinned this comment just to say thanks for watching my video, and I hope you are having a very nice summer.

[jimsvideos]

First concrete and now soil? Man this guy is totally undermining my rope business.

[iDubbbzTV]

Great vid. I was always confused why channels like codyslab confidently walk through a ghetto mineshaft without fear of collapse

[ThisOldTony]

I had my doubts.. until I saw that yellow #2 mechanical pencil in your pocket. Great demo as always!

[parthmistry]

Thank you for putting your ankles, shins and knees on the line to show us something really fascinating. Never thought this could be done.

[OmegaPaladin]

This video in particular finally explained to me how ceiling bolts work, despite visiting multiple mining museums. I think your gravel demo would be an amazing addition at the Coal Mine exhibit at Chicago's Museum of Science and Industry. You've earned my Patreon support.

[azyfloof]

I would _never_ have guessed that pinning the gravel like that would work, and be load bearing! That was an impressive demonstration :D

[burt]

Could see the pucker factor rising as you stood on the test rig. Really cool demonstration, thank you!

[biglar]

Very cool topic. My Father worked at the copper mine near White Pine MI for about 20 years. He explained the production cycle - of which "Roof Bolting" (as they called it) was the final step prior to drilling the next series of blasting holes in the heading.

One problem with roof bolts is that if the shale chips away from above the bearing plate, the bolt is left doing nothing - it's just hanging from the anchor pin and no longer helping to support the ground around it. (Imagine removing the pieces of gravel that were in direct contact with your lower washers. It would collapse like a house of cards.)

The (now closed) mine at White Pine claimed to have pioneered the idea of using resin to hold the roof bolts in place. The hole is filled with resin and the bolt is inserted with a hardener packet and spun in order to mix it. It worked so well that they actually started suspending their conveyor belts from the roof bolts with no problems.

The equipment they used was nothing like the manual operation shown in the video though. A "roof bolter" was a large (not tall, but "thickly built") machine that used a gatling-gun-like device to drill the hole, fill it with resin, push in the bolt and hardener, and finally spin the bolt home. All done from the driver's seat of the machine. Each bolt was 16' long and they were spaced 4' apart.

[patrickbastos]

I've seen these bolts used in rocky hills very close to roads. I've always wondered how some screws protected me from slidings, now I know. Great content.

[SteveFrenchWoodNStuff]

That was a very impressive demonstration that I never would have thought could possibly work!

[TheBetterGame]

Potash Miner here! Loved the video, we use rock bolts with expanding wedges (for some reason we call them shells) every day, LOTS of them.

[MalcolmCooks]

i would never have thought that gravel could be made to support the weight of a man just by putting bolts through it...

[nicoinformatics]

"Tunnels Don't Collapse, But Sometimes They Do!" -Practical Engineering

[AbuSousPR]

in Syria.. when we were under siege for 5 years..we dug tunnels like this to bring in supplies and to build hospitals & shelter

[JanPeterson]

The most extreme example of this bolt tensioning of rock I've seen was in the Cheyenne Mountain complex. I had the opportunity to tour the facility as an AFROTC cadet in 1983 or 84. The complex was hollowed out under the mountain and around 115, 000 bolts ranging from six to twenty-five feet long were used to tension the structure as you describe here. There is also a lining of chain link fencing material to catch any chunks that might flake off. Great video.

[jdhsingi]

Very interesting...Thank you for sharing.

A video on pumping concrete underwater as in large bridge footings in a river or sea, would be interesting.

[sodaPapa]

Grady is starting to become like a V-Sauce of engineering to me

[Leanzazzy]

6:20 This man is going above and beyond just to show us how important and practical engineering really is. Show him some love 💗

[claycav]

Im 6 months on the job as a geohazard mitigation technician for a Colorado based geotechnical company, GSI if you've heard of us. We do a lot of soil nails and shotcrete walls for public infrastructure around the country. On an emergency landslide job outside of Salem. Your videos are very interesting and very helpful understanding this line of work I cherish deeply. You should do one about micro-piles, high tension mesh, and shotcrete, I feel that they would make interesting and helpful videos for myself and the general public. Thanks and keep up the great work!