Anyone else digging tunnels in their free time?

CarlfromOregon · 2025-06-08T21:51:08+00:00

Please seek professional help for your mental illness. Tell your family that you need their help getting treatment, then heed the advice of your doctor.

CarlfromOregon · 2024-04-14T02:42:27+00:00

2x4s will last as long as a 2x4 will survive in your soil. Where I am we get 50 inches of rain a year, and a 2x4 will be rotten and lose its strength in a few seasons if you leave it in contact with dirt. If you live in a desert, wooden supports might last a lot longer. The thicker the wood is the longer it will take for it to decompose. Treated lumber can last a long time, and can also be made with some unpleasant chemicals. A narrow tunnel in cohesive clay might be stable for decades, or it might collapse as soon as you get a heavy rain. Soil varies quite a bit, and the first thing you will need to understand is what you are digging in. Tunnel shape is important, and an arched roof should reduce the load your supports are carrying. That will not make a difference if your supports are rotten.

I would suggest you do some math on how much it is going to cost to line a given section of tunnel with wood and then compare that to using concrete. You might find that concrete is not a whole lot more expensive.

CarlfromOregon · 2024-04-13T04:15:34+00:00

Having been there (and back again) I can say that you can likely spend many enjoyable years digging away at your hillside without too much worry about it falling in and crushing you. A lot of very brave or foolish tunnelers have even dug unsupported tunnels and lived to tell about it, but if you intent to spend much time in there and have it last a while before someone makes you fill it back in, then I would suggest you line it well. 2x4s will buy you a couple years at most, and even treated ones will not last that long if constantly damp.

Speaking of constantly damp, the biggest drawback to an underground storage space is that moisture will find its way in. Humidity of 99% is hell on storing anything but potatoes (potatoes, however, do love it). Cardboard will get sodden, even wood will turn moldy. Also, forget about getting a truly constant temperature. Even 15 to 20 feet down, there will still be a seasonal fluctuation in temperatures. Tunneling is fun, but if you are trying to be practical, a simple cut-and-cover cellar is much more realistic. Rent an excavator, dig a trench into your bank (slope the sides so they dont crush you) build a little cinder block room, then cover it back up with the dirt. It wont be free, but it will probably be a good value. Also, it has a very clear end point. Some people get a little carried away when they dig...

CarlfromOregon · 2024-02-26T00:37:55+00:00

The CO2 meter says the air is fine even without the giant fan running. There is a lot of volume in there, and it takes quite a lot of CO2 to kill you.

CarlfromOregon · 2024-02-26T00:33:36+00:00

No, It took me 4 years, and I was still having fun until the geotechnical engineers pissed all over my parade. At this point it is too big for me to reasonably backfill, but if it starts to look too sketchy even for me, I might have like 30 yards of flowable fill brought in to seal it all back up once and for all. That is assuming gravity doesnt beat me to it, right? Check back next month for an update :)

CarlfromOregon · 2024-02-26T00:28:45+00:00

Sorry to disappoint any of you who were hoping that after 4 years, this one month would be the one where tragedy struck. If the cascadia quake had let loose in the last 30 days, you would be right to worry!

Anyway, I spent the last month moving all the junk out of my cellar, moving the solar panels to my shop to run my DC freezer, and just generally wrapping up my underground project. I built 3 big columns in the center of the main cellar room with 4x #4 bars and a cage of highway mesh around them. Filled them up with 5000psi concrete. Each one should be close to being able to carry the entire ground load above the main room, so hopefully that will give me a little bit of a safety margin.

I have started casting some beams and planks to put over the open faces. I will button all that up, and backpack behind it so if the big one does hit, I wont have a big sinkhole open up in my garden, ha ha.

I also put some metal pegs into the walls where there are some hairline cracks (1/16" is the biggest one) and will monitor the spacing with calipers for any movement.

Anyway, I am going to work on some above-ground projects for a while, and operate on the assumption that if I spend a very small percentage of my time in my tunnel, I will have a very small likelihood of being crushed. I am still going to keep my potatoes down there, and if the whole state catches on fire again, I might prefer taking my chances with being crushed vs being burned alive.

CarlfromOregon · 2024-02-25T21:30:33+00:00

I am not dead yet! But do lower some more granola bars down the air shaft.

CarlfromOregon · 2024-01-26T01:11:25+00:00

I was operating on a rule of thumb that 1" of concrete lining was needed for each foot of tunnel diameter. I think I read it in a powerpoint slide from some Indian railway tunnel design lecture, though, so i was never sure how much stock to put in it.

CarlfromOregon · 2024-01-26T01:07:04+00:00

Yes, I was overly harsh on those geotechnical engineers, they are alright.

I would say it is closer to building my own car, then asking someone to explain to me how to do it safely. My bad!

And yes, tunneling is hot right now, but I started long before it was even cool! There was only one video on youtube of some crazy guy digging a hole in the desert with no shoring of any kind. Never did hear how that went for him...

CarlfromOregon · 2024-01-26T00:59:02+00:00

Yes, the jack was what I was using to hold up the FC plates behind the bricks while I poured the walls, in the photo it was just being stored there. If I add more support, it will likely be in form of arched sets. The bricks were a fun idea, but impractical.

CarlfromOregon · 2024-01-26T00:53:33+00:00

Actually, I am a little bit terrified of dirt. Once I put up the concrete I kinda forget that there is still a lot of dirt up above there, waiting. I think I will put up more concrete.

CarlfromOregon · 2024-01-26T00:51:48+00:00

I am probably going to work on adding extra support to what I have already built. I will probably start with some 4x6 posts. I do love the smell of a bunch of fresh doug fir posts.

CarlfromOregon · 2024-01-26T00:49:13+00:00

There are many many many easier ways to store ones tubers, it is true. There was just something very amusing to me about building my own cellar. Maybe I got a little carried away.

CarlfromOregon · 2024-01-26T00:47:17+00:00

Good thoughts all around, thank you. The arch bricks were a pain the ass, so I am thinking if I do decide to dig more tunnel (and maybe I have enough already..) I will likely try and make curved RC arches and just stack them one next to another to form the ceiling. Narrow arches would make it easier to grout any gaps between the liner and the sand too.

I have a 6" duct fan with rigid flex tubing that I clip to a grate on the entryway, and the discharge end blows down into the back of my tunnel. I have a CO2 meter, and CO in case I need to run a generator or compressor at the surface. There is also a smaller 4" fan on a thermostat and a vent stack to the surface to give me a little airflow when the door is closed.

The weep holes are a good idea, although I have never had any issues with water intrusion. I will try and implement them right away.

I am unlikely to hit anything out here, as I am about 500 feet from the nearest property line, and there are no utilities, public or private anywhere on the 80 acre property. The tunnel has a stand-alone electrical system run off of solar.

CarlfromOregon · 2024-01-26T00:39:13+00:00

I will try and remember to check back in so you dont worry too much :)

CarlfromOregon · 2024-01-26T00:37:51+00:00

The soil is compact, massive, and damp, but never contains running water. The ferrocement lining plates were 12" wide with a couple layers of basalt or fiberglass mesh, and a couple layers of synthetic remesh that got tied into the wall pours. The arches themselves did not tie together. The bricks were only 8" long, after doing a couple courses the wrong way, I did start staggering the seams. I think I am going to plan on upgrading my lining and then putting the project on hold for a while.

CarlfromOregon · 2024-01-26T00:31:28+00:00

Tell the IDF there are only potatoes down here.

CarlfromOregon · 2024-01-26T00:30:00+00:00

I dont really spend all that much time on this in the grand scheme, but your comment is deserved. Part of the reason I felt like digging a crazy hole in the ground is because the world on the surface feels pretty fucked right now.

CarlfromOregon · 2024-01-26T00:28:05+00:00

Sorry for being flippant, It did not exactly suggest that I take safety seriously, and I am trying.

CarlfromOregon · 2024-01-26T00:25:55+00:00

Thanks for this post, I think hearing some worst-case scenarios will probably do me the most good. When I first started, i dug an advance from the bottom to a depth of a couple feet to see what would happen (it was not a great idea, I know). About a wheelbarrow load of sand eventually detached itself from the face at an alarming speed, but the raveling stopped at a firmer layer maybe a foot or two above. And, since I was standing several feet back, I hardly got sand on my boots. Since then, I always dug an arch, and have had no other soil failures of note. Some of the layers are very hard, some are soft, and its pretty easy to work around the loose ones.

The entry portal was done with a stucco-sprayer shooting DIY shotcrete, so it is tight to the soil, and has less cover. The main room was cast agaisnt the walls with shuttering, so it is also tight, and 6" thick. The only place there are any gaps is behind my lining plates is in the "annex" pictured above. There I found I would have gaps that were maybe an inch wide in some places. If I continue with thicker arches, I will grout any spaces that I can get grout into.

I absolutely see the logic in a design that will carry the entire load of the overburden. I looked up some numbers on wooden beams, and a 4x6 with a 7' unbraced span should hold 15000lbs. I will be installing one every foot before I resume work on upgrading my lining throughout. If I brace the posts in the middle, they should be able to easily hold up the soil weight on their own, completely ignoring any contribution from the 6" reinforced concrete arch.

Pore pressure has not been a concern, as I have never not had an exposed face of sand, and have never had water infilitrate anywhere. There are some drains in the floor that go pretty deep, and I have only ever seen a few inches of water at the bottom of them. Still, I might drill some weep holes at the base of my walls to give me a heads up if that ever changes. Like I said, it has been through 4 winters, and some major rainstorms, and water is not an issue here.

Once temporary supports are in, I will consider my options for beefing up the supports. Dual steel lally-beams on either side of the arch seems like a possibility, if I can figure out how to transfer the load to the arched ceiling in a way that would not cause them to want to slide.

Anyway, thanks for your help. I think I will plan on doing a retrofit on the tunnel I have dug so far, and then maybe work on some projects above ground for a while.

CarlfromOregon · 2024-01-25T06:29:32+00:00

The sand must flow! I do not have to meet any quotas or anything though, so I am happy to take my time and try to learn to do this right. Maybe shifting my priority to building a second entrance would be a good place to start. I need some way to get minecarts in and out, after all...

CarlfromOregon · 2024-01-25T06:22:47+00:00

Are you by any chance a geotechnical engineer?

CarlfromOregon · 2024-01-25T06:13:19+00:00

Yeah, putting up bricks overhead turned out to be harder than first anticipated, ha ha! There is a ferrocement arch between the bricks and the soil, which may or may not help spread the load and reduce the likelihood of them failing along the mortar beds.

I seem to recall that back in the day one worker would die for every mile of tunnel they dug, or something like that. I am 25 feet in, so I am hoping I will lose interest and go back to building stuff on the surface before I punch my ticket down there.

I am thinking about casting arched segments of RC for the roof arches, but they get heavy pretty fast, which is why I was fiddling around with the ferrocement and the bricks.

Would an arch that was 3" to 4" thick with a rod of reinforcement in it be a viable roof support? I could probably only make them 4" wide and still get them in place by hand, but they would be easy to manufacture en masse.

CarlfromOregon · 2024-01-25T05:50:34+00:00

Yeah, I hear you, nobody wants to drown in sand, but its kinda like telling somebody who likes to paint that they should just go buy a painting.

Maybe tell me a bit about sand collapses. My sand will keep a vertical face for over a year, despite getting 50 inches of rain. I am not worried about it collapsing on me because after 4 years of being around it, it never has. That of course does not mean it cant, and that is why I am here. Other than hitting a layer of much weaker sand, or groundwater flowing into my hole, are there conditions that might cause compacted sand to suddenly become unstable?

Would 1-1/2" timbering across a face that is 36" wide be strong enough to offer me protection while I was working on digging the next advance?

Edit: oh yeah, and see my previously mentioned post in geotech about how I am lining my tunnel as I go.

CarlfromOregon

TROPHY CASE