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Mini Excavator and basement dig

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52K views 25 replies 12 participants last post by  rino1494  
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#1 ·
I have a Kubota KX121-2 mini-ex at my disposal, more time on my hands than money these days and a desire to build a decent workshop/garage on my property.

I would like to build the workshop in a basement underneath the new two car garage. I am confident at doing all aspects of the work including the foundation however not so about the excavation.

While I have used tractors on the farm years ago, I have never used an excavator nor a backhoe and I have done nothing like dig a 26' x 26' x 8' deep hole in the ground.

This is a background task so I'm in no hurry. I wonder if a mini-ex with a 24" bucket is big enough to tackle such a dig? If so, what is the safest way to go about digging that deep of a hole with one?

Thanks
 
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#4 ·
An 8' hole will be difficult and take a whole lot of time with that machine. It really depends on what kind of earth you are excavating. Your excavated dirt will need to be moved a safe distance from your work area. You will need some sort of loader or a bigger excavator. Grade and lay out needs to be established by an experienced contractor, engineer, or surveyor. Experience with the earth in your area is learned with years of ground work. Time is your enemy when you are dealing with a wall of dirt especially if it gets wet.
 
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#5 ·
Yeah, in days gone by I always sub'd out for things like this but you never know, I just may like this kind of work and it's a good opportunity to try it out in between other projects. Turns out this mini-ex has an enclosed cab that will keep my dry during the winter -- I like that!

Still hoping some skillful operators might pass on a few pointers.
 
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#6 ·
MikeyJP1980: Silly me, I forgot to mention the lot is completely flat and I do have a dump trailer at my disposal. According to the soils report, there is a good amount of clay in it which makes it harder to dig but it holds together well. The soils report says to dig 3' at a 45 degree bevel and then 5' straight down per OSHA.

The good thing is I know the end goal, now I just have to do the digging part.
 
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#8 ·
Set your 4 corners, paint your lines and set your machine up along the line so that you will be digging a trench that is 3' wider than the line. Do not make it less than 3'. You need room to construct the foundation, place drain tile and tar the foundation. Also, since you will be doing this at your leisure, when it rains, part of the dirt will fall in the hole and you will have alot of shoveling to do.

Dig your trench down along the line before you start taking out the middle. You need to do this to keep a vertical excavation. I dig a trench, then take a pie shape and keep working backwards. When you hit a corner, dig 3' past the corner then come down the other side and keep taking a pie shape. Not sure on your reach, but you may have to dig the back wall, 1/2 of the 2 sides, then come in the middle and hog out the middle.

Start in the back and work your way out to the front. Don't do the opposite. I've seen guys do that and get surrounded by dirt at the end. Depending on the stability and moisture of the dirt, I'll dig the full depth and create a 2'-3' bench for safety and to prevent dirt falling in from rain.
 
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#10 ·
Thanks rino1494,

This was the kind of suggestion I was looking for. Basically, trench the full depth along the back wall in a straight line. Then dig out a pie shape from the back corner at full depth, then a pie shape from the front corner at full depth and then repeat again for the two corners on the other side and I would be done.

Only things is my mini-ex wouldn't have the depth or the reach to get 8' down when a safe distance from the edge. I'm thinking I would need to do the dig in layers such as 4' at a time. I have seen large commercial projects done this way.

For instance, I could do the first 4' as you suggested above. I wonder what would be the best practice to then dig the remaining 4' to complete the excavation?
 
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#11 ·
If you do not have that much reach, you are going to be screwed when bailing dirt. You are going to be moving it 5 times to get it far enough away from the excavation. May I suggest renting a track skid loader to dig the hole. My dad used to dig all his foundations with his 955. That was years ago before he had an excavator.
 
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#12 ·
I have a good size dump trailer I was going to use to move the dirt onto the other side of the lot where we want to build up the landscape to create some privacy. After the first 4', I guess I can make a ramp where I can load the trailer while I dig the remaining 4'. Much quicker to move the dirt that far with the trailer than the mini-ex.

A skid-steer is another idea. I guess if I was going to rent something I would probably rent a bigger excavator instead to go with your first suggestion.

Thanks for your comments. It's great to be able to bounce ideas off experienced people.
 
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#13 ·
I have a 121-2, you should be able to excavate to that depth easy enough. It just doesn't have much reach for that size excavation, it will take some time to move the soil out of the way.
What size trailer do you have? If it's small that will limit the speed of the job anyway.
So it just comes down to how fast you need it done.
 
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#14 ·
I think I can get 3-4 yards in the dump trailer easy.

I'll try digging out the deep trench as suggested. I've only dug shallow footings with it so far which I know it does fine.

With the limited reach however, I'll still have to make a ramp and get down and dig the center.

Fortunately I've got more time than money right now so I don't mind it taking longer.

I wonder how many hours your KX121 operates on a full tank -- assuming typical use?
 
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#17 ·
fhdesign: I didn't know the KX121 had the power to dig at that depth. I guess I'll have to try it. My trailer will hold 3-4 yards which isn't a lot but I would have to use it anyway because I have to haul the dirt all the way to the other side of the property. That said, I'm lucky to have a need for the extra soil right on my property. In a way, I'm kind of doing two projects at once with this dig.

I suppose I will have to watch out for those batteries on the trailer. I'll have to use the 7-pin connector with the Aux line that charges them as long is the motor in my truck is running.
 
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#18 ·
I think your machine can handle the depth. 8' seems awful deep unless you are using at least 9' walls. Drainage is key to a good subsoil structure. If it is going to take a long time excavating the hole the more the chance of rain. If it is flat your basically digging a pond. Water can make this rather simple project a monster pain in the rear. Control the water and take your time and you will be fine. Make sure you set a benchmark that will not get disturbed so you can maintain grade. You have about 200 yds. of undisturbed soil. I do not know the actual amount of gain you will have after the earth is excavated. I know its a whole hell of a lot. You have a lot of dirt to move with an electric hydraulic trailer but remember you will have to back fill and grade so do not take it all away. 3' over dig is the standard all over the country. Set your square, paint your lines, set your grade with benchmark in a good location, and start to dig.
 
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#19 ·
I will be digging in the winter unfortunately so rain will be a factor. I was thinking of covering the sides with plastic so at least the rain won't hit them directly.

Not sure about the bottom though. There won't be any slope to the grade so yes, I will be digging a pond sort of. Fortunately the water table is far below this and we don't typically get much rain since it's California. I suppose I could rent a pump, set it in the middle and just pump the bulk of the water out onto the property. After a few days the soil would be dry enough to walk on.

I really just need enough time to put down some drain lines and then a 3" working slab and I'll be OK for the most part.

One other question, I do need to pile some soil close by (about 80 yards or so) for back fill. What is the closest yet safe distance I can keep this pile from the hole?
 
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#21 ·
If the machine and bucket are in decent shape it should easily have enough power to dig at that depth. Moving the material with that small of a trailer will be the slowest or most challenging part of the job. If it's decent material we try to keep the backfill material as close to the excavation as possible, graded off flat so you drive on or over it. If it's wet material or something that you can't drive over or work on when it gets wet then we would stockpile it out of the way.
 
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#25 ·
I like 3' over dig although that is about the limit. It is tough to excavate footers, waterproof walls, lay pipe, or fight 100 lb. wall forms in anything much less. Less is definitely better when it comes to disturbing earth. With a solid wall and good clean washed rock for backfill no one should have any trouble. I prefer to work smarter not harder so I will stick with the extra room next time we excavate a basement.
 
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#24 ·
dayexco: Hire someone else; deliver pizzas??? That's not rising to the challenge. Besides, I know of several guys who would love to jump into the Kubota and start digging just for the fun of it. I have to include myself in that crowd. It's not often I get a nice piece of equipment like this to play with. Now that I have a plan to go about the dig, I can't wait to get the permit to get started.

After I have a good day of digging, then I'll eat the pizza!
 
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