Bunker -wood post thickness!!

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champo

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Joined
Oct 17, 2022
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Location
Southampton
Hello, so I want to build a bunker.

Well not really a bunker more of a trench.

My question is this , after I've dug out the actual trench I'm going to lay logs across the top which would sit under a tarp.
I want it to be flat on the surface (not a mound)
So with 3 feet of earth on top of the tarp that is on the logs above the trench.

How thick do the logs have to be to prevent collapse?
Logs will be made of pine and fresh cut and untreated.
They will also be laid next to each other horizontally to cover the trench.

Thinking of makings the trench more of a square if possible so more accommodating.

Possibly 7ft by 7ft

Any help or advice would be great appreciated.

P.s can we not get lost on the design or any other detail, it's the thickness of the logs I'm concerned about.
 
1) Water is not a friend to wood so I would highly recommend doing something to protect that wood from moisture rot.

2) Three feet of earth is not that much especially if you are laying whole logs one nestled up to the other.
1666095838250.png

The logs being used here are about a 4" diameter or about 7-8" across the entire end they taper very little. If you will note, there is more log on the soil than spanning the gap...so NOT getting into the building details, it is pretty well impossible to give you a safe answer.


Pine, fresh cut, still needs to be protected from rot and I see termites are also an issue in Southhampton England. If you are concerned about collapse, defiantly would treat those beams or encase them in concrete!

Termites can turn a damp 8" log into cork pulp with 0 structural integrity in about 6 months....

How are you going to do the walls? Dirt walls? What kind of dirt? Cement block? That will also determine how large of a diameter log you will need.
 
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Thanks for the reply.

The logs will be under a tarp so protected from rain and moisture in the soil.
The ends of the logs (where cut)will also be treated with a preservative
Only airborne moisture to really worry about.

We don't have termites here.
Will be using dirt walls.
Using concrete is not an option here.

I understand wood will not last as long as concrete but as long as it lasts roughly 10 years I have no issue replacing the logs then.


Cheers
 
Results will vary depending you your geology and climate. Here in our area, the pine log will be mush in less than a year because the tarp will trap moisture and heat coming from the ground, and create a perfect environment for fungal growth.
Been there, done that...ruined a bunch of oak firewood that way.
But at least I was able to get some beautiful spalted oak for knife handles, LOL
Red oak should look something like this:
1sskUTI.jpg


But after sitting under a tarp, it was "spalted oak." The black lines are boundaries between competing fungus colonies in the wood, which is what makes spalted wood. The wood had to be stabilized because it was technically ROTTEN.
dPkKzOU.jpg

aPJpArk.jpg

7UwfhU2.jpg
 
Wow they all look absolutely amazing.
I love the marbling effect of the spalted oak.

So ends of the logs which would be completely covered by the tarp would be treated with wood preservative.
The rest would be under the tarp on the surface but underneath would be in the open air.
I could treat all the logs with preservative for the whole length
 
The logs being used here are about a 4" diameter or about 7-8" across the entire end"
 
This doesn't make sense, if the diameter is 4" the how can it be 7-8" across the end?
 
The logs being used here are about a 4" diameter or about 7-8" across the entire end"
 
This doesn't make sense, if the diameter is 4" the how can it be 7-8" across the end?

They mixed up radius with diameter. .
 
Hello, so I want to build a bunker.

Well not really a bunker more of a trench.

My question is this , after I've dug out the actual trench I'm going to lay logs across the top which would sit under a tarp.
I want it to be flat on the surface (not a mound)
So with 3 feet of earth on top of the tarp that is on the logs above the trench.

How thick do the logs have to be to prevent collapse?
Logs will be made of pine and fresh cut and untreated.
They will also be laid next to each other horizontally to cover the trench.

Thinking of makings the trench more of a square if possible so more accommodating.

Possibly 7ft by 7ft

Any help or advice would be great appreciated.

P.s can we not get lost on the design or any other detail, it's the thickness of the logs I'm concerned about.

Make a big hole, throw in an old shipping container and fill the rest back up, you can always throw some logs over the container before you put soil over it that will withstand normal Russian bombs.
 
This is a popular technique to cheaply and quickly protect wood from water.



I can definitely confirm that works. I used to do stump grinding and often times people would try burning their stumps just to find the parts that didn't burn become permanent lawn decorations that are 5x harder to grind out than the unburnt stump would have been. Another trick is to dry distill deciduous wood to produce pyroligneous acid and brush that on like stain. Although simple, it is a messy and somewhat dangerous process.
 
I would think about RR ties. My wife used them to cover a drainage ditch across the property when she was developing it. Tin, galvanized sheet metal on top DG on top of that.
I think we had one failure in 25 years on that 100 ft ditch.
 
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Has anyone thought to use old cold room panels they are normally 1.2 mt wide and about 2.4 mt long I used them back in 1991 to cover a French drain 15 mt long ( covered over with soil ,some have metal channels in side if they came from a butchery ) that I dug on the smallholding for the septic tank to drain through , I sold the property in 2003 , to my knowledge it is still in place
 

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