Digging a big hole

[shane]

Better heed the warnings on this one or what your calling a storage hole will become what most folks call a grave.

 

[CurlyDave]

I'm digging it for underground storage - long story.

I would re-think this whole idea. This is a very inconvenient way to store anything, and unless you have a much larger yard than you imply, will cause you enormous problems.

If you live in any place with a building department and zoning, you will need a permit for this -- so much for a "secret" storage facility.

Don't even think about doing it without one, the neighbors will know and probably won't like a pit nearby.

Anything like this will have to be disclosed when you come to sell your house -- think what that would do for resale value.

The other question to ask is: where are you going to put the dirt that comes out of the hole? It isn't going to just disappear on its own.

The walls will be made of 2x6s stacked up and then backfill around it with gravel. The soil is clay...I don't think there is any risk of anything collapsing.

I think there is a significant risk of this collapsing.

The walls of this finished hole are going to be 10' high retaining walls. You need a professional engineer to draw up plans and stamp them. 2x6 walls, even with gravel behind them, will not handle a 10' wall.

For a well-drained wall, it is permissible to consider the earth and gravel behind the wall as a fluid with a density of 40 pounds/cubic foot. Unless you know how to calculate the force this will produce on the wall, and then design the wall for it, you will be in a world of hurt.

Speaking of well-drained, how do you intend to prevent this from filling with water when it rains?

- - - -

If you live in a rural area and want to build a "survival cache" you should have enough land to do this right.

If you live in a place where you don't have enough land to do it right, consider this nightmare scenario. You get half to 3/4 done with the pit when someone notices and complains to the government. They send out the building inspector who will immediately put up a stop work order, and eventually some government authority will force you to fill in the hole.

Now you have already disposed of the material that came out of the hole, so you are going to have to truck in material. So much for minimum disruption to your yard.

- - - -

I live on 40 acres in a place where almost anything is allowed. If I wanted a hole like that I could get it approved by calling it a test shaft for a mine. Mining is specifically allowed.

If I wanted to store something that size, I would never even consider underground. I would rent a storage locker until I could build a shed. And, how are you intending to put whatever you store in there? Unless you have a crane, everything in that gets in there is carried in by hand, probably down a ladder.

But, I can put a lot of survival gear and food for my family for a year in a medium-sized closet, without needing any underground storage.

 

[EddieWalker]

I think Dave gave you some very good advice. The size of the hole you are digging is going to require some very serious posts to hold back the walls. If it's ten feet deep, then you will need some massive posts set very deep into the ground. Somethine like this will require an engineer to calculate based on the soil conditions. I would never try to guess this, and I build for a living with some experience doing things like this.

What are you going to store there? Wine? How would you get it in there? Ladder? Stairs would take up a huge amount of a very limited amount of space.

If you tell us your plans for this and your reasoning for going down, we might be able to come up with some advice. As it is now, and with what you have said, it's not something you should do. If you are not worried about your own safety, consider what it will be like if your wife, child or just about anybody was injured or killed from either falling into it, being next to it when it fails or inside of it when it collapses? This is the type of project that will change your life in a very bad way if you persue it in the manner you have suggested.

Just to answer your question, a full sized backhoe without an extend-a-ho is capable of digging a 12ft hole with a flat bottom. With the estend-a-ho, it can go a few feet deeper. I've dug holes like this for septic tanks and it's not as simple as just operating the controls. position the backhoe is critical to keep the walls straight, and even more important is having a plan on what to do with the soil that comes out of the hole. When a hole gets to a certain depth, the amount of dirt that comes out will quickly fill up the surface area and start dropping back into the hole. Operating the backhoe controls takes some time to figure out also. Some people pick it up in a day or so, others take years. My Dad is one of those who took years to get the hang of it, but even then, he still makes some doozy mistakes. One was to push a tree the wrong way and take out my neighbors fence when there was all sorts of room in the other direction. A mistake next to a 10 foot hole could put you in debt for tens of thousands of dollars in damages to the backhoe, or kill you.

There are no bad ideas, just poor planning.

Eddie

 

[Willis Fecon Bushhogging]

Hmmm...well, I might have to go back to the shovel idea then. I want this to have as low of an impact as possible on my yard...and digging a ramp for a big tractor would ruin most of it. I'm digging it for underground storage - long story. The walls will be made of 2x6s stacked up and then backfill around it with gravel. The soil is clay...I don't think there is any risk of anything collapsing.

I'm thinking maybe about using a tiller to loosen up a layer of soil, shovel it out, and keep going. I need the exercise anyway.

I wonder, is there some kind of industrial vacuum I could rent to suck the loose dirt out of the hole?

I wouldnt even ask my best laborers to dig a hole that big, in clay. I think if I did lose my mind and ask them to do it, they would quit. Im not saying it cant be done(there are different kinds of clay) but I will say its a project, you need to hire out. If you were in my area, I would probrably charge you around $700-$800, $400 of this would be to move the equipment. They charge us $200 each way for a local move (Cat 320L excavator) No longer than it would take, I would just get the lowboy, to standby. Moving/spreading the kind of clay we have in my area (wet, soggy, heavy) with a front end loader will be interesting. I have had to stock pile clay from a basement and just wait for it to dry out, before I could do anything with it. I dont agree with some people, that you should go rent a excavator, heavy equipment is very dangerous and you need to know the equipment to do a job like this. If you were going to dig a shallow drainage ditch, then I might say, go for it. In my area, the rental places requires that you have insurance to cover the machine (Im talking regular backhoes, excavators, bulldozers, etc) I think they charge $300 a day, plus transpoetation, plus tax, for a mini excavator and if its the hard wet clay, we have it wouldnt dig it, well maybe in 2-3 days you might get a hole.
Im finished, go hire someone that knows what he's doing, if you still want to dig it by hand or rent a machine, do your wife and children a favor
"BUY LOTS OF INSURANCE ON YOURSELF"

 

[Pennsylvania Weldor]

My John Deere 410 Loader/Backhoe would have a hard time doing this hole. I have the long boom allowing me 15' digging depth. It could be done with a back hoe, but really a job for an Excavator. They are more manueverable and job would get done much quicker.

 

[MidnghtOwl]

Some great points raised, but one isn't getting enough attention. If your digging in clay, all your going to create is a swimming pool unless you start really putting in a massive drainage/pump system. For the walls, I don't think you can consider using wood frame of any kind, even green treated rots when exposed to wet earth. (let alone the engineering) If your commited to making this project work, I think you need to go with Fold-Form concrete walls just to hold back the earth. I have two window wells 6.5' deep on teh side of my house, 5' windows 5 foot between them. My retaining wall is right at 9' deep and 18' long. (i'll take pictures and post them for you). I build a wooden wall during construction using 4x4 posts 4 feet apart and 8 feet below grade, I spaced 2x6's every 2 feet running up the length and placed 5/8" green plywood over that, then started backfilling. I didn't even make it up 4' before the wall started leaning toward the house. Sooo brought a backhoe home from work, dug it all out again, and dug footing for a concrete retaining wall. Current wall is 8" thick of poured concrete. Thankfully i'm in sugar sand so water retention isn't a problem here.

 

[MidnghtOwl]

Some great points raised, but one isn't getting enough attention. If your digging in clay, all your going to create is a swimming pool unless you start really putting in a massive drainage/pump system. For the walls, I don't think you can consider using wood frame of any kind, even green treated rots when exposed to wet earth. (let alone the engineering) If your commited to making this project work, I think you need to go with Fold-Form concrete walls just to hold back the earth. I have two window wells 6.5' deep on teh side of my house, 5' windows 5 foot between them. My retaining wall is right at 9' deep and 18' long. (i'll take pictures and post them for you). I build a wooden wall during construction using 4x4 posts 4 feet apart and 8 feet below grade, I spaced 2x6's every 2 feet running up the length and placed 5/8" green plywood over that, then started backfilling. I didn't even make it up 4' before the wall started leaning toward the house. Sooo brought a backhoe home from work, dug it all out again, and dug footing for a concrete retaining wall. Current wall is 8" thick of poured concrete. Thankfully i'm in sugar sand so water retention isn't a problem here.

 

[MidnghtOwl]

Some great points raised, but one isn't getting enough attention. If your digging in clay, all your going to create is a swimming pool unless you start really putting in a massive drainage/pump system. For the walls, I don't think you can consider using wood frame of any kind, even green treated rots when exposed to wet earth. (let alone the engineering) If your commited to making this project work, I think you need to go with Fold-Form concrete walls just to hold back the earth. I have two window wells 6.5' deep on teh side of my house, 5' windows 5 foot between them. My retaining wall is right at 9' deep and 18' long. (i'll take pictures and post them for you). I build a wooden wall during construction using 4x4 posts 4 feet apart and 8 feet below grade, I spaced 2x6's every 2 feet running up the length and placed 5/8" green plywood over that, then started backfilling. I didn't even make it up 4' before the wall started leaning toward the house. Sooo brought a backhoe home from work, dug it all out again, and dug footing for a concrete retaining wall. Current wall is 8" thick of poured concrete. Thankfully i'm in sugar sand so water retention isn't a problem here.

 

[Ridgewalker]

If 12 x 12 and backfilled all sides how are you planning to get in? Are you going building something on top? If so you're really going to need some strong supports.

 

[Erik_in_Hoyt]

can you do this as a walkout?
if yes, you might consider digging the hole and dropping a piece of 12X9 concrete culvert in it for a near instant shelter.then all you'd need is to put in a block wall at the back - or pour it - and frame out your front wall/entry.

good luck!