EDIT: 07082012 Finally gonna finish it up in next few weeks....
When I built the house I just spent 7 years working on, I had a lot of days that were just plane monotonous, so I would daydream about the Next Great Project as soon as I finished the house...
If you're OCD you know exactly what I am speaking about.
Perhaps it was watching too many reruns of Stollag 17...
Maybe it was all the Underground cabins we built as kids to have a cool place to hide out in the summer.
Truthfully though I just love to build things and when I designed the house I made the bottom level only half the size of the main floor and the other half is a crawlspace about 4 foot high.
Most of my plumbing and stuff runs around the floor joists down there so I wanted enough room to have access to everything but I didn't want to build an eight foot wall, It took me 7 weeks to do the block for the garage workshop and storage room so saving 4 feet of wall seemed like a good idea.
Looking back if I really intended to do this and had the wife's permission I could have saved a lot of bother by doing this first and I wouldn't have to worry about the house falling on my if I dug out too much from below it.
I didn't leave any vents to the outside mostly cause of wanting to be energy efficient and not have a cold room under one above I was trying to heat in winter. I did talk to the building inspector about this and convinced him I could put a gable vent fan on a timer at each end one blowing in and the other blowing out to ensure a good change of air so it never mildews. I intentionally made it to push air into my workshop and draw replacement air under the house at the far end of the garage. This way in the winter when I am using the wood burner if I am working on something I can open the duct to the workshop and close the damper and the heat travels in a big circle across the garage into the crawlspace and then back into the workshop to circulate the heat so I can work on something midwinter if it is 40 out with a t-shirt on.
I got lost in a Blizzard when I was abut 20 for 23 hours and was 31 miles from where we parked when found, so I don't do cold anymore...
When I laid out the supports to the crawlspace I left a wider gap between two of the columns supporting a beam since the crawlspace is 20 foot wide and I didn't want to pay to special order 20 foot 2 by 12's and I just happened to have gotten a deal on a couple 40 foot beams delivered by accident to my house and unloaded before we discovered they loaded the wrong ones and were two thin to support the bottom garage ceiling. They sold me them to me at cost when they delivered the proper beams a few days later because it would have cost them money to rent a piece of equipment to lift them back on the truck.
I also filled the back of the bottom garage wall wide enough for a ten foot door and didn't put any rebar in that section. All the rest of the bottom level block has rebar in ever other hole and is filled to the top with concrete instead of just every 4 feet as code calls for. I will be able to saw this opening or get some of that ACME black paint they use to make tunnels and then start digging with a bobcat and dumping the dirt on the slope behind the pool so its not as steep a grade since I use a push mower for the exercise.
Step 1: Different Methods of Moving Soil and Reinforcing Sides
When I started thinking seriously about starting this I knew I had to do a few simple tests first that would cost me a bundle if I had to hire an Engineer and do them even before I applied for a permit.
They'd want to know the different types of soils, how thick each seam was and most importantly I wanted to know how far down the water table is.
I live in Florida and generally if you dig a hole a few feet down you'll hit water but I'm in the Panhandle of Florida so we actually have some hills here. The lot slopes to the lake enough I was able to dig a bottom level into the hill giving me a pretty safe place to hide if we get a bad hurricane. The house is extremely reinforced and all the walls are shear walls meaning at least one side has plywood glued and nailed every four inches, including a second layer on the inside of the outer walls which also went a long way to soundproofing the place. I have more anchors than required and threaded rod going from the footers to the trusses including the interior walls.
The molding work on the ceiling of the great room is actually tied into the roof trusses and the floors are all 3/4 plywood tongue and groove and glued and nailed plywood every four inches for a subfloor. It's covered by 3/4 by 2 1/4 Oak tongue and groove running perpendicular to the floor joists. The Kitchen, Halls and Bathrooms I tiled but the bulk of the house has the Oak making a very stout roof for the bottom level.
My workshop also has plywood ceilings so that part is especially strengthened to the point of a tornadoes shredded the top two floors you'd be safe huddling under the work benches.
I tend to ramble because I crushed my head three years ago in an accident so back to the intended topic of how to dig a hole under a house and not have it fall on me.
My primary method was that I felt I could safely dig along side of a footer and pour a 2 foot high concrete wall so long as I did it in stages the sides would not cave in for a few day, especially if I misted it with water from the hose. I drove rebar about a foot into the sand or clay and left the rest sticking out the top so the final bottom to top pour would bind everything together. I also after the concrete had dried and I had the forms moved down another 2 feet I would use a small spade to find the bottom of the previous rebar, and using a piece of pipe for leverage I'd bend it into the area of the new pour at a 45 and then bind it to the rebar for the next pour. The end result is a very solidly secured concrete wall 10 or 12 feet high shaped like an inverted wedge to discourage it from sinking into soft ground. Also I decided to only do 10 or 15 feet at a time but never the length of an entire wall in one shot so I didn't have the sides blowout like in a mine accident.
I spent 7 years building the house I don't want to cause it to collapse and the wife would never let me hear the end of it.
I then figured I could keep repeating the process essentially forming a very tall staircase and when I had enough head room I'd pour a final layer 8 or 10 feet high to tie it all in. Billy down at the building department would have a fit if I told him I wanted to do this and I'd need a real engineer to put their stamp of approval on it and it's not the type of job you can start and walk away from halfway done if something comes up, so this is too much for me to do as a solo project and I;m not actually Licensed Florida Contractor.
I did figure I should do a test shaft to see if it actually worked and get a record of what was down there and I would definitely need to know the water table height and the thought of having to assemble a mini drill rig in a crawlspace seemed pretty expensive but by staring long and hard at it for a time and a day, I decided I could dig a shaft by hand right next to the access port and cover the stairs with a snug piece of plywood then shovel it out the port onto the stairs then into wheel barrows and dump it out back.
How hard can that be?
I had a limited budget but I do own a mortar mixer and had a great stockpile of rebar and three inch pvc pipe left over from something I cannot recall and some lumber I'd used already for concrete forms and yes there is a Plus side to OCD especially if you have the room to store it until you need it.
I chose not to mention to the wife what I was planning mostly because she would have said no but I had just about used up all my savings finishing the house but I still had my emergency $1000 so I did some math and bargained for a lower price on 80 pound sacks of Redi-Mix if I bought 6 pallets and so I snuck a look at the wife's calendar to see her next doctors appointment and her caregiver would drive her so I set up the deliver for when she was gone and had a space cleared in the bottom garage that I could store all of this, and had some pieces of pipe on hand to walk like an Egyptian and move the 3000 pound pallets to the far back of the garage by rolling then and then using the next pallet to roll the first to the back until all six would be safely hidden inside.
The wife was running late though and they showed up just as she was leaving...
Fate Strikes Again but my wife knows I was still not quite right in the head in fact she'd say I was like that even before hitting my head and is used to me just jumping up in the morning to start working on something and I did after all build her a house and miraculously she didn't ever really ask me what the cement was for.
Once I had the cement I thought about forms and I decided if I am to do this and make a 2500 square foot bunker I need the forms to be modular so I could keep reusing them over and over.
I decided on a few basic sizes, 2' by 8',2' by 6', 2' by 4', 3' by 4', and I made them with the braces in each size identical so when I needed to make 50 of these I could drill around the perimeters in a standard pattern so I could just bolt these together, pour the concrete, then unbolt them the next day and move on. Trial and error taught me that staple gunning a smooth layer of 6 mill plastic makes for a much smoother wall than plain plywood and you just need to replace it every few pours.
With the forms made and the 6 yards of concrete safely hidden and covered with a tarp just to be safe I started digging next to the access port so I could get some standing room. The first five feet of soil is sand I believe referred to as Orange Ruffie but I'll need to check my soil survey of Walton county to be sure.
Regardless sand is pretty easy to shovel although the very top layer was had dried out pretty solidly and had some clay mixed in I had to spray it with the hose to soften it up. You actually need to keep the sand moist or the sides will cave in quickly and I made a point of misting the ground before I quit working on it for the day.
I made this approximately 7 by 7 since as I went deep it would get narrower and I was about 18 inches between two columns supporting the beams so this was a good spot to test. On the first 2 foot pour I also poured and formed a beam between the columns with a lot of heavy angle iron cut to fit tight between the columns.
The I started getting the hits from The Office of Homeland Security which I figured was just because so my of my traffic comes from Walter Reed Hospital and the rest from our troops abroad.
Then the cable company knocked on my door and said some magic piece of equipment let them locate the source as somehow coming the crawlspace under the house and they needed access under there to check for problems...
Step 2: Ten Yards of Sand by Hand Out in the Yard
I made a big dent in it, the hole not my head, but that to has a dent but only the size of a tennis ball.
A mere dimple compared to shoveling out 10 Yards of sand by hand.
For a time the pick and shovel bumped the floors joists and my wife started asking about the noises where? What could be causing it and well and this is actually true I have a perforated drain line that runs around the perimeter of the monoslab making up the garage floor, about 40 yards of concrete and at times of heavy rain the water would sometimes back up this pipe and actually cause the bottom row of block to wick some moisture out so one of the factors in choosing this location was that it was in the center of the drain line and I figured when I found it I'd think of something and when she asked of the noises I thought well I'm just digging a hole to run that pipe into so it drains well and keeps the bottom level dry and patted myself on the back for being quick on my mental feet and actually coming up with a valid reason to dig down there.
By now I was pretty proficient in digging using the tower of babble approach and was getting strong again but really 10 yards was making me wish for a better way and then I looked at my 3 inch trash pump and the pile of three inch pipe and by now I had gone down a good 4 feet below the bottom level floor and had hit a seem of very water impervious clay that would hold water for days.
Sometimes you just get lucky!
I also looked up and saw my 1 1/4 central water supply line and added a T and a valve plus a spicket for a hose and I could draw up the max the 2 hp well puts out and fill the hole in no time then while its running start the trash pump with the flexible line in the drink and it pumped as much sand out as I could shovel in, slurry style and I could pump out a yard in five minutes or so plus I stretched the hoses out so it deposited the sand in the low spots of the yard I had always been meaning to fill.
It was surprisingly effective and on a bigger scale I'd get a second trash pump to deliver a large volume of lake water up to the pit since I had to constantly pause to let it fill back up with water.
It also ran my power bill up a bit...
I continued this pouring two feet at a time although you can go 3 or 4 feet without the walls caving in when dealing with clay but better safe than dead so two foot at a time and ever other 2 feet I drill a hole with a water jet at a 45 into the layer of clay then shot a piece of 3 inch pvc 5 foot long again with water, drove a piece of rebar about a foot into the clay past the pipe incase I ever ran into it from the other side I could tie the rebar together and ended up with 12 fingers extending into the seam of clay and tied solidly to the walls rebar so they could almost hover if you dug out from under them.
Once I had about 18 foot of headroom I jetted a ten inch piece of schedule 80 about 15 feet down so I could get an idea where the water would because and by my rough guestimate I was as low as the lake is high so I figured the water was near and sure enough it's almost 25 feet below the dining room floor, very unusual, and apparently the seam of clay is acting as a sort of underground dam since the seam follows the contour of the ground and free of the pressure of a layer of clay above it, it rises up the pipe to about 5 foot below where I stopped going down.
I did this to have a drain.
I would not want to come home and find the bunker has turned into a swimming pool because a pipe broke and the ten inch pipe filled with gravel would have been very effective and require no power.
OCD rears its head and I remember I have some 2 inch sch 40 and about 15 feet of 2 inch well screen and so I shot the well point down about 60 feet then filled around it and the inside if the ten inch pipe up almost to the top with gravel so nothing could fall into it. I temporarily hooked a half horsepower well pump to it and ran about 8 gallons a minute for 30 hours to get all the fine settlement out so I figure it should be able to drain almost as fast as it empties. Plus it could serve as an emergency water source if we ever get slammed by another Katrina and have to go a few months without power since only having to lift water 5 feet can easily be done with a hand operated crank.
Step 3: So in Conclusion...
The house did not fall so I would say with a real engineer telling me how to place the rebar I can dig down about 21 below the dining room floor, there is a 4 foot crawlspace, 5 to 6 feet of sand then about 20 feet of clay sitting on top of the water table.
Two stories would be possible but I am thinking it would be better to have one floor with 12 foot ceilings with everything gently sloping to the drain in the center and I could have an easy 1200 square feet of tornadoes proof shelter, enough for the entire street according to FEMA. It's not likely that I'll build the big bunker since I'm pretty close to being tapped out, need a few more surgeries, and it's not likely I'll ever get hired to do anything since without a short term memory I spend a lot of time walking around trying to remember what it is I am doing. They would need to hire someone to follow me around and keep reminding me what I was working on at the moment but it might make for an interesting Discovery Channel Show...
LOL If you're gonna Dream a Dream don't ever cut yourself short.
When I had the accident I had the house dried in but it was just sticks inside no wiring, plumbing etc. Fortunately I had the siding on already since that took a month but I hadn't bricked the bottom level yet and I managed to do that in about 2 years by putting a white board up in the Foyer and every morning when I arrived I'd write down what I was planning on working on and I finished the house and relearned how to walk and talk since somehow I fell through the medical cracks and was never actually sent to any therapy or rehab but maybe it worked out better this way.
If worse comes to worse I'll just turn this into a stairwell and make an 8 by 12 foot room under one part of the bottom garage floor which according to http://www.fema.gov/hazard/tornado/to_saferoom.shtm
it is the safest place to build a shelter.