Originally Posted By Gerri:
Originally Posted By 1_BIG_BUNKER:
Hi Gerri, I got an email saying someone had some questions about this, and they're good questions.
I looked at that web site you linked us to, and they did give us some good info there.
First, the reason I say three feet of earth is because in most cases, three feet is enough when you also take into account that the dome itself has around 10 inches of concrete in it as well, which increases your protection factor inside. Most people do not build a bunker too close to ground zero unless they have no choice, so they will automatically have time and distance on their side.
Now if you HAVE to build a bunker 1 mile from ground zero, three feet or so of earth will still be enough to protect you because at that close of a distance, the ground shock wave will be massive, and for anything to have a chance to survive, it will have to be equally massive. That means you don't have 10 inches of concrete, you have three FEET of concrete, plus the three FEET of earth between you and the outside world.
Now if every 5.5 inches of earth halves the rems coming in, then 3 inches of concrete should do about the same. Actually I believe it's 2.25 inches, but we will use 3 just to be safe. Now with three feet of concrete, that adds another 12 levels of protection above and beyond what the earth is giving you already. So go back to your chart, and start at three feet of earth and count down another 12 levels or so and see what you will be getting inside your shelter.
Just to give you an idea what kind of pressures we're talking here above ground, an EF-5 tornado with 300mph winds produce 404 pounds of force per square FOOT or about 2.8psi over pressure. In their chart they do not even begin to talk pressure until it is at 8psi or three times that of an EF-5 tornado.
Now if that's what's happening above ground in just plain air, what happens when we have a rippling force traveling through the ground coming at you? The closer you get the more rems you take in but also the more violent the forces you and your shelter are going to experience and the more massive you will need to build. A dome is designed to handle 2000 pounds per square FOOT or about 14psi so anything as far as a storm goes is easy to handle, but when you exchange moving earth coming at you instead of air, that's a game changer. I mean a 20 foot wall of water moving 25mph coming at you is very destuctive, so imagine what the ground will be doing to you near ground zero.
Other things to seriously consider is how you're storing supplies if you're that close to ground zero. It's onething if a roll of TP flies off a shelf, but another if glass jars of food start flying around. You just lost supplies. Just look at videos of earth quakes and you will see what I'm talking about. You can't just build a normal shelf and expect it to work when the violence start if you're that close or even in an earth quake area.
I hope I explained this clearly. It's late and I haven't been to bed yet.
As far as the filter goes, thats based off of the common filter most can afford when building a shelter. Plus it operates without electricity, so someone will have to be by itside pumping it and it's nice to be doing that around others instead of off all alone. Plus the manufacturer has designed it to be placed inside the shelter with you.
Here's what I'm talking about.
Originally Posted By Gerri:
1BigBunker, I don't know if you're still following this thread or not. I was hoping to find out how thick the walls would need to be if this were buried 10 feet underground measured from the top. In other words, ~30 foot deep hole. Would this require two layers of rebar?
Now as far as this question goes, what sizes are we talking here? If you're talking a tunnelish type of thing like in the link in my first post, then I wouldn't worry about it at all if you went 15-20 feet wide and as long as you wanted, and had #4 rebar, 60 grade and 12" on center up to the 8 foot mark, and then tighten the pattern up to 10" OC. I would do the floor at 12" OC with the same rebar, 60 grade #4 and do the ring beam with 60 grade #5 and do four runs of that around the ring beam.
Remember, rebar is for tension, and concrete is for compression. Piling on tons of dirt puts that structure in complete compression mode, so while adding more rebar won't hurt, it won't do much to help unless you're talking serious ground movement due to being at ground zero. Then you'll need it.
For the shotcrete I would do 12" from the floor to the 8 foot mark and then taper it to about 6" and keep the dome as a half sphere or close to it. You can flatten it out some if you want, but I wouldn't go less than 40% of your diameter. So if you were 20 feet wide, from the top of your wall and where the curve of the dome starts, I wouldn't go go any flatter than an 8 foot arch.
I would also seriously reconsider going down as deep as you're talking. It costs money to dig that deep, and if I explained myself clearly, you don't really need to. You won't be digging just that hole, men can not work in a 30 foot hole. It has to be tapered out and a road built down into it so trucks can pour the floor.......unless they won't be and you will do it yourself. In any case, it has to be tapered out or someone will die if a 30 foot dirt wall gives way.
1_BIG_BUNKER, thank you so much for your answers.
I totally agree that the radiation table they came up with is really just a best guess based on assumptions they've made. I might add to some of your thoughts regarding that table. First, they assume a surface burst. As you point out, that will move dirt around and would be completely unsurvivable if you are at or near ground zero. I'd expect surface bursts to be rare unless it's a terrorist using a railroad car or shipping container. It isn't worth it to live in a big city, near an airport with a 7,000 foot + runway, or near refineries for lots of reasons beyond just being a target for nuclear warfare.
All of these types of tables depend on knowing lots of variables. Is the weapon was surface or air burst? What size is the weapon? How far away? How much shielding? If the shielding includes dirt, what is the moisture content? After the prompt radiation from the initial blast, then you have to worry about the fallout. That depends on knowing the wind direction and all the upwind explosion details. Also, if it rains, the runoff might cause fallout accumulation nearby.
In other words, it really is too complicated to know with any certainty. The most useful conclusion I came to after looking at that table was the very bottom. If you go deep, it doesn't matter what the variables are. After 10 feet, it's all good.
That's why I was asking about adding a couple feet of earth on top. I was using the 32 foot wide, and 16 foot tall dome you posted when I was asking about construction details. It seems like this would need 16 feet to ceiling, 1 foot thick concrete, and 3 foot of earth for a total of a 20 foot hole. Probably another 2 or 3 feet to put in a footer and gravel bed for radon removal? If I wanted to add another 7 feet of dirt, I'd need about a 30 foot hole. I'm well aware there is a big risk of cave in. I really like Utah Shelter Systems web site
; however, the picture midway down shows this nice vertical wall that I'm assuming is somewhere in the high Utah desert. Every time I see those pics, I'm thinking there is no way that could be dug that way most places even if the water table didn't prevent that depth. Whether I'm digging a 23 foot hole or 30 foot hole, either way, it's going to be a pain in the ass and expensive. I just don't know if it would be all that much more expensive or not. Would the specs you mentioned apply to the dome instead of the tunnel like structure as well?
Regarding the air filter, thanks for the link. I didn't know there was any American manufacturer of blast doors, blast valves, and ventilation systems. I suspect we may be talking about two different things. I agree with your approach of having the emergency hand pump located where everyone can help. The difference is the filter needs to be somewhere shielded. The filter will be catching contaminated particles which will be giving off a lot of radiation shortly after any explosion. It's not clear to me from the link what American Safe Room recommends. I can't tell from their website how they recommend the actual filter be installed.
Thanks you very much for posting so much great information here. I'm always on the lookout for your comments.