Theory behind bunker construction - Anyone ?

[defender130]

After visiting the Kelvedon Hatch secret nuclear bunker while we down that way a couple of weeks ago i have been trying to work out the basics behind the construction of them


The main thing i cant work out is how it was laid in one, the info inside said the basic concrete structure has steel rods embedded as reinforcing every 6 inches and the walls are however many feet thick, the whole structure was poured so the pour stayed wet and there where no weaknesses from joins in a dried section of concrete where a new section was added on top of it

Even i can work out that there are then many tons of wet concrete sat on top of many tons of slightly drier concrete but is it really as simple as making a massive reinforced and braced steel cube to plonk on top of the first loads that make up the base then filling in the sides and over the top or is there a better way of doing it that doesnt involve massively heavy lifting gear to drop a cube on the wet stuff before trying to continue the pour around it

Or would the cube be built in place with a steel outside shell and then the reinforcing rods holding the steel inside shell in place and use of very wet pour and vibration to work it into the middle

I would have thought with that bunker been three levels high inside that the weight of concrete pushing downwards in the sides would have been massive and without huge bracing or support the sides would have just bowed inwards under the pressure

Anyone know how it is done, my brain is hurting trying to work it out

[womble]

https://en.wikipedia.org/wiki/Slip_forming

They use concrete that will set fast enough to accept the weight of the concrete that's been poured on top of it, and pour at the right speed that the heavy wet stuff doesn't overload the load-bearing stuff that's gone "off". While concrete takes a lonnnnng time to go completely off, it gets pretty strong, pretty fast, so the "right speed" isn't intolerably slow.

[defender130]

Now that makes a little more sense, thanks Womble I would never have come up with slip forming as I have never heard of that method before

I like to know how things work and how they are built / made so I have learnt something today, time to go and Google for more info now you have me in the right direction


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[womble]

I Googled for "continuous pour concrete"; I first encountered mention of the technique on some Discovery Channel (or some similar medium) prog about building skyscrapers.

[Wulfshead]

Assume that any shuttering will stay in place, reinforced and able to accept the next load right the way up to the require level.
Until the concrete has set the reinforcement od shuttering IS the strength of the wall.
After the shuttering has been struck the walls will need tanking to withstand water ingress.

I'd like to know if the bunker was built with wooden shuttering or steel shuttering.
I loved doing timber shuttering, anything for an excuse to get off the trowel .

Wulfshead

[poppypiesdad]

Low water content concrete and using a high amount of vibratory compaction usually it holds it own . Its just over damp and it sets quickly . The main problem is having enough water in it so the concrete can set and evaporation then the concrete cracks . Although i wonder if the ground moisture would help that ......


J

[defender130]

I guess with a full size bunker being continuous poured a full mixer load of 6 or 8 cube at a time is only going to even out at a couple of inches height increase at a time, assuming some massive shuttering design that can be raised as the concrete height grows it would only need to be a couple of foot tall

I keep thinking (out loud) constructing one in the garden is a good idea and my wife seems to be coming round to my way of thinking

I guess the outer side of shuttering could be done with steel and the reinforcing rods welded in place ready and the inner shuttering done from hollow concrete blocks with concrete and rebar in place down the holes so they hold tight while you pour

With only 6 or 8 cube going in at a time a decent sized garden bunker isn't going to gain massive height or pressure on shuttering with each load if it was spread evenly around via a concrete pump and boom holding the pipe up so it could just be swung around slowly as the concrete chugs out
Main problem is I think the water table round here is too high so it's probably a non starter other than in my head


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[poppypiesdad]

So an above ground bunker or a hardened room inside your house may be a idea ?

J

[defender130]

We were thinking of doing the cellar as it isn't really a full cellar in the normal sense because the floor only goes down about 3 foot lower than the rest of the house

Only thing that put me off is we are in a radon gas area and I didn't want to disturb any currently sealed pockets under the house whereas in the garden they could empty and dissipate without affecting the house

I suppose I could dig the far side of the garden until I hit water then fill with gravel and build on top of a gravel damper then cover over with earth afterwards to hide it, we would just gain a hill in one corner


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