I've been pondering a second house under the one I just finished building bunker style for tornados and just because it would be fun.
A big part of the labor involves moving the sand and clay from under the house to the backyard and if you've ever watched Escape from Stollagg 17 and really thought about the dirt in the socks trick, a Yard of Sand is a Lotta Socks...
I started with a crawl space under about half the main floor of the house, and about 4 foot of head room, and a 3 by 4 foot doorway halfway up the steps or four feet above the bottom garage floor.
Pyramids have always fascinated me, the shear tonnage of them and I always wonder what they are resting on, the backgrounds always seem to be sand that can flow over time and they have stood for so long a simple shape transferring energy over a large base and when I was thinking of the bunker Idea realizing in Florida at some point I was going to dig into a water table and a heavy pier might over time sink like the Kansai Airport, KIX not being built by kids and needing hydraulics and such to keep it sitting level I thought that an inverted pyramid would be less likely to sink since to go down you'd need to also push some vector off in a horizontal type way and then I thought some more and having been hit in the head but not necessarily made foolish I guestimated 2 feet as about the maximum cliff you could dig into a seam of sand and have it expect to stay put as long as the sand was kept damp and if it collapsed it would probably go to a 45 or so meaning if I stayed more than two foot plus a fudge factor away from anything that might be adversely effected by having it's legs pulled out from under it, in the most broad sense of the term it should be fairly safe...
I added 2 and 2 and a few more and decided the simplest thing to do would be to dig down two feet, form a temporary wall about 4 inches thick, drive some rebar a few feet into the ground and tie them to some running horizontally inside the pour, carry in a few hundred 80 pound sacks of concrete mix, pour the wall, telescope in and repeat the process a few time digging down to pull the rebar from the first pour at and angle and tying it into the rebar for the next one and then when it was 4 or 6 or however many feet high depending on the load next to it I'd form one more wall and end up with vertical smooth walls that are thicker on top than they are at the bottom just like an upside down pyramid.
The deeper I go the less floor space I have but it seemed doable and since I watched the well be put in and dug the very large hole seven years ago into the hill so I could have a level mostly below ground for hurricanes and such, this being Florida after all and things happen, I had an idea of what type of soil was down there, and new there was a seam of clay that was fairly thick and guess that since the lake is about ten feet below the height of the bottom garage I probably could come close to being able to dig down at least one story without it turning into a sinkhole but I also new it would be unwise to just start building something without first taking a look at what was really down there so I decided on a test shaft to test construction methods and get soil samples at certain depths and most importantly how deep you can dig without hitting water since dampness and closed up places don't go well together and an ideal emergency shelter is ready at a moments notice even if it has not been maintained for a decade.
At least I think so since I have seen many 1950's era bunkers built for the cold war that are now long flooded because it costs money to run a sump pump.
Fort Walton Beach is full of them if you look hard...
Step 1: Walk Like an Egyption
Being not Lazy but hopefully practical I realized there wasn't much fun in working in a four foot crawlspace hunched over and for the time being the only way in and out for anything was the door way halfway up the stairs, I figured it best to start near the opening to save the distance I had to shovel but not so near that you'd need a ladder to crawl down under the house if a pipe broke or something and compromised by first digging down 2 feet below the opening which let me stand up as soon as I got under there and then dug to the left of that and cleared a ten by ten floor area for the test shaft.
This was just sand but under normal situations the crawl space stays very dry which is more dumb luck than anything so I would need to spray it with the hose a bit to soften it up since there is a small amount of clay in it as well.
I started by cutting a sheet of plywood wide enough to fit over the steps forming a ramp between to block walls filled with concrete once again having spent many moments pondering the building of Pyramids it's entirely possible I meant to do this when I first laid the blocks for the bottom level just like how the supporting columns in there holding a beam so I can have 20 foot spans above are spaced so you could knock a hole in the back wall of the bottom garage in an area that just happens to not have rebar like it was meant to be sawn open with a partner saw and then drive a BobCat under there and go to town but that would imply long term planning and possibly lead to a much longer post than intended but it was pretty simple to shovel sand out the opening then when I got a big pile shovel it into wheel barrows and use it to fill in lowspots in the yard.
And it was good exercise!
Step 2: Start Strong
The test shaft was to be centered between two columns and the concrete block filled wall of the bottom level and although I wouldn't want to just pull out the two columns to see if it worked, the way the beams are run the floor above it would still stand although I imagine it might develop a bounce if you hopped around in the dining room so once again it appeared a reasonably safe place to start experimenting and since I like thing stout and on resting on a good foundation, and since when working top down the Foundation is on top but still first I began with a foot thick perimeter wall connecting both piers to the main wall and full of very heavy scrap steel including a tightly fitted I Beam between the bases of the two columns and rebar bent and wrapped around the columns and then left protruding past the pour to tie into the next section of wall and also having done it before when I built my dock, knew I could jet a piece of pipe down a pretty far way if I had enough water so I used a flexible pool skimmer hose connected to an 1 1/4 inch water line and shot down 4 ten foot sections of 3 inch sewer and drain pipe down so they would come up inside the first pour, dropped a piece of rebar in them and filled them almost to the top with a sand and cement mix. I hit clay at about 6 or 7 feet so I ended up with some ten foot posts resting in the seam of clay and then tied the rebar into the walls which are tied into the columns and concrete wall.
And thus I had my Footer to lock everything in place.
Step 3: Repeat Over and Over
Digging is good exercise.
It's not so bad when you just need to throw the dirt just waste level but as I went down not to Babble on Babylon and Towers but I reached the point I had to shovel from pile to pile in a circle each time to a higher elevation to get it out the 3 by 4 opening and into the wheel barrow and out to the yard and I think it took a good two weeks to move out about ten yards of sand.
Every time I dropped two feet in the shaft I stepped in a wall and since I was closer to the clay I shot two lengths of 3 inch pvc at 45's on both sides and again filled them with cement and rebar and wove it all together as I went down then came back and poured taller walls inside to smooth things up and to square things up.
Digging is good exercise but you really can have too much of a good thing.
It took me 7 years to build the house although I did get quite a bit delayed when I hit my head, but I'm not sure I'd have the patience to repeat such a long process and in the back of my mind I am thinking of the sand quarry up the street where I get my fill and also cleaned masonry sand and I remember the barge and the gigantic vacuumed pulling sand from the bottom of a water filled pit of blue.
I have a 3 inch trash pump that I use to shoot posts into the ground when I'm building a dock or seawall you can drill a ten foot hole pretty quickly and get them sunk in the lake bed and I had already used it to make a few holes in the lake bottom around the dock for the fish to hide in so I figured if I could fill a pit with water and suck it out I could shovel sand into it and shoot the sand out at the same time.
I realize the chance of having both a concrete lined pit and an 8 horsepower trash pump are preponderous but these things happen and after all, I had a lot of time to day dream about this as I did redundant tasks building the house above.
Step 4: I Just Had To
And so to get to the point of this instructable after some experimenting while the wife was not home I managed to move about 20 more yards of sand without having to use a wheel barrow but using a lot of water...
I had to fill it up with a hose basically which took maybe an hour since by now it was a pretty big pit and then I had to hoist the 50 foot flexible line up to the back deck and prime it backwards with a hose, but I could move about a yard of sand out at a time in five minutes before I ran out of water.
I didn't see this as a problem in the long run though since I live on a lake and I managed to demonstrate the ability to make a really deep concrete box redundantly reinforced and one day I stood at the bottom and Looked UP and realized it was a long way away to the bottom of the house and I had enough headroom to fit a room under the bottom garage floor with ten foot ceilings.
That seemed far enough and I was puzzled at not hitting water especially since I could actually at this point using a solid length of 3/4 flexible water line about 300 feet long pull a siphon from the drought low lake level to the bottom of the pit and have it flow uphill from the back yard...
I reasoned the seam of clay was acting like an underground dam and followed the contour of the ground above and to back up since I should have mentioned while doing all this digging I determined that there is about 5 feet of sand sitting on a seam of clay about 22 feet thick more dumb luck try and find a hill in Florida.
I decided to pour a solid floor at the bottom of the shaft to lock in all the walls and act as a Header even though it was down there where a Footer would normally be but since I wanted a drain and had some ten inch pipe I dug down another 5 feet and finally hit water, then just because as I said I wanted a good natural drain and had the pipe I managed to shoot down about 10 feet of the big pipe and left about four feet sticking above the ground, then poured the floor and I basically had a concrete wedge shaped box that was 7 foot square at the top on the inside and about 10 foot wide on the outside and tapered down to about 6 foot wide on the outside 4 foot on the inside so it would look like an arrow head pointing down.
It took 8 yards of concrete, in 80 pound sacks and then another 2 yards to pour a lid on it so I didn't fall down the thing but I reached the point I had my data and a big hole in the ground and got everything secured since I was about to have surgery on my shoulder for a torn rotocuff and would need a break or if I got bored with it and found something more exciting to do it could sit there for decades without me ever having to worry about the thing caving in plus you never know, I could get hit by a bus or something.
Step 5: Finally Finally a Point to All This
My thought was if I ever actually managed to get a permit to build a proper bunker with fake windows and flat screens to stream scenes from around the planet according to ones mood, I would need to move out a lot of sand and clay and while it's fine to while away a few odd hundred hours on frivolous things like test shafts if I was to get under there with a bobcat I'd need a pretty dependable way of getting the spoils out or I'd be making a lot of trips back and forth up the hill which in itself is fun but in the real world I'd need to be pretty quick about getting the walls down and the less time spent just driving around is more time to pour concrete so I came up with a more permanent idea of making a very large check valve and forming a concrete basin to shoot water in and pump a sand slurry out as fast as I could scoop it in with the bobcat.
Dumb luck again or OCD I save things and happened to have a large weight from an old tool used to cut grooves in long leaf pines to collect the sap. I found it on my tree farm but it was missing the blade and the handle but I kept it even though at the time I didn't have a clue what it was.
It's a hundred year old 2 pound pear shaped piece of cast iron with a one inch hole through the middle of it and fits inside a 4 inch piece of schedule 40 but not in a 3 inch piece.
I stared at the odd pieces of 3 inch pipe I had from the previous attempts at sucking sand out from the crawlspace and got a 4 inch T with a threaded opening and some glue and a stainless steel bolt from Ace, made a few cuts and used a piece of chain I had laying around and managed to make a fairly decent check valve that lets a large amount of sand flow around it and with a bit of tweaking like slipping a piece of pipe around the chain to force more water up the pipe so it primes faster the thing actually seems to work.
I adjusted the height the weight rises by using the bolt though a link at the foot of the pipe so that it stays pretty centered in the T which has a little more room than just a section of 4 inch sch 40 and it rattles a bit but in a test run it moved a few wheel barrows worth of sand in a couple minutes with just 3 feet of water at the bottom of the pit.
I'm going to use a piece of pipe as a sleeve in the weight to force more water up the pipe than slips past so it primes faster but I don't want it absolutely water tight in case it gets clogged with sand I can just unscrew the access port at the bottom of the pipe and flush it out with water. You need to inject a strong stream of water right in front of the intake to keep the sand mixed up so I have the pipe resting in a five gallon bucket that I'll trim down to about 5 inches so the sand doesn't wear away the concrete but I believe if I could pump about 100 gallons a minute up from the lake into the pit as I sucked a slurry out with the trash pump I could move it out fast enough to keep up with me dumping BobCat sized buckets of sand into it and could use sand fence to collect the sand and use it in my back yard.
I'll mess with it a bit then when I get back to work on the bunker if ever the next step is a few big arches to tie in the columns to the far side of the crawl space and support a future ceiling and I'll install it permanently since it will also be useful if the thing ever flooded like an under ground swimming pool...
Some Assembly Required.
Step 6: In Action!
PS, The sun lines up with my house and shines in the back window and out the front door just as it sets on my birthday...
Pyramids facinate me.