This post covers how to use a compressor and a pneumatic excavation tool, made in this case from copper pipe, a ball valve, and fitting, to dig under a concrete slab without a lot of effort. For small hole, a 1/2 inch 3 foot copper pipe works fine. I use my small compressor with about 50 PSI, mainly because I am not in a hurry and can wait for it to store up air.
This hole under a 3 foot concrete slab took about 3.5 hours. The intended pipe was a 1/4 inch sprinkler pipe so I didn't need anything more than common stuff you would have at home: a screwdriver, ear defenders, electrical cable, and about 20 feet of 200PSI compressor line.
I learned about air spades when working at General Dynamics and they were a potential system for mine clearance as they spread pressure around an excavating land mine; this means they could expose landmines with lesser risk of initiating fuses. In those applications the air pressure could be much greater than what I would recommend using on home made versions.
In this case, the goal is to use air pressure to expose and remove just enough dirt to run a pipe through.
I made this air spade out of copper because you need a semi-hard metal that can take some force from prodding and withstand enough pressurization. I solder the shit out of the connections, they are full welds and can survive prodding into the ground and scratching on concrete.
A reducer nozzle soldered to one end, a 1/2 inch ball valve soldered to the other and a compressor fitting is all you need.
I use 50 PSI and crimp the reducer into a venturi. You want an opening that can't swallow a rock so it runs without bursting the pipe, and can be used to prod and loosen rocks and soil. While you aren't digging with a shovel, you are actively stabbing the rocks and soil to jar loose rocks. The air pushes loose fill out the hole.
Copper won't take steel-type forcing, not without exploding or bending so you will apply steady firm force and move the tip around. Since the parts for this amount to $30 or so, I would recommend replacing one after a few uses rather than risk splayed copper shards in your hand.
You could go without a valve but this way you can build up pressure.
This is the hole location, running a 1/4 inch pipe under sidewalk to the irrigation pipe in the garden. We, I, shovelled out 2 tons of gravel and we are going to lay sod in the dead space under the Mugo pines. Last step with our hot dry climate is irrigation!
First dig out small holes and remove enough vegetation you can be comfortable working on both sides. The holes start small and you are going to work from both sides but in case there is a large rock don't dig out too much- you might be moving. Air spades can't break rocks - at least not small ones. You want to dig shallow holes from both ends. As your spade gets longer into the hole, you want to extend the holes on both sides so you keep the spade under the concrete and not digging a larger hole.
The steeper the angle, the longer the hole and in the future the softer steeper hole will pour moisture into it which you don't want for frost heave reasons. You want the hole hugging the concrete. N.B. I blow out my lines in the fall so they aren't going to freeze.
Once the hole is prepped, you can begin. Of course you are working from both sides so you only have to go about half way from either side. This air spade could dig a whole sidewalk from one side but it would take longer.
I start loosening with a screwdriver and while you are working excavate the loose soil from the hole mouth.
Important, the more dirt you clear from the hole mouth, the more air will push dirt right out of the hole for you. If you don't clear while you work, you will just dig more yourself. Let the spade work. I did leave the spade on and went for a pee break and it did some work blowing out loose dirt but you really need to actively grind to work faster. Stab, blow, and remove loose dirt are the repeated actions.
Here's a small video from the excavation end.
Notice how the angle of attack is lower as you dig out the entrance.
I use gloves even though it's low pressure because the venturi might rip skin back and I normally have skin tears on my hands. I've seen the video of compressors ripping skin back to the elbows, not worth the risk.
I use a prodding motion and alternate working both sides.
Once you have gotten the spade fully in, you will see dirt shooting out the other side.
The gravel spoil on this photo came from the middle.
Last task is to feed the pipe through the hole. I tape the pipe to the air spade and shove it through.
Line is through in 3.5 hours in this case with dry soil that consisted of clay and sediment.
Thanks for reading my how to/ hoe to guide to air excavating.
This hole under a 3 foot concrete slab took about 3.5 hours. The intended pipe was a 1/4 inch sprinkler pipe so I didn't need anything more than common stuff you would have at home: a screwdriver, ear defenders, electrical cable, and about 20 feet of 200PSI compressor line.
I learned about air spades when working at General Dynamics and they were a potential system for mine clearance as they spread pressure around an excavating land mine; this means they could expose landmines with lesser risk of initiating fuses. In those applications the air pressure could be much greater than what I would recommend using on home made versions.
In this case, the goal is to use air pressure to expose and remove just enough dirt to run a pipe through.
I made this air spade out of copper because you need a semi-hard metal that can take some force from prodding and withstand enough pressurization. I solder the shit out of the connections, they are full welds and can survive prodding into the ground and scratching on concrete.
A reducer nozzle soldered to one end, a 1/2 inch ball valve soldered to the other and a compressor fitting is all you need.
I use 50 PSI and crimp the reducer into a venturi. You want an opening that can't swallow a rock so it runs without bursting the pipe, and can be used to prod and loosen rocks and soil. While you aren't digging with a shovel, you are actively stabbing the rocks and soil to jar loose rocks. The air pushes loose fill out the hole.
Copper won't take steel-type forcing, not without exploding or bending so you will apply steady firm force and move the tip around. Since the parts for this amount to $30 or so, I would recommend replacing one after a few uses rather than risk splayed copper shards in your hand.
This is the hole location, running a 1/4 inch pipe under sidewalk to the irrigation pipe in the garden. We, I, shovelled out 2 tons of gravel and we are going to lay sod in the dead space under the Mugo pines. Last step with our hot dry climate is irrigation!
First dig out small holes and remove enough vegetation you can be comfortable working on both sides. The holes start small and you are going to work from both sides but in case there is a large rock don't dig out too much- you might be moving. Air spades can't break rocks - at least not small ones. You want to dig shallow holes from both ends. As your spade gets longer into the hole, you want to extend the holes on both sides so you keep the spade under the concrete and not digging a larger hole.
The steeper the angle, the longer the hole and in the future the softer steeper hole will pour moisture into it which you don't want for frost heave reasons. You want the hole hugging the concrete. N.B. I blow out my lines in the fall so they aren't going to freeze.
Once the hole is prepped, you can begin. Of course you are working from both sides so you only have to go about half way from either side. This air spade could dig a whole sidewalk from one side but it would take longer.
I start loosening with a screwdriver and while you are working excavate the loose soil from the hole mouth.
Important, the more dirt you clear from the hole mouth, the more air will push dirt right out of the hole for you. If you don't clear while you work, you will just dig more yourself. Let the spade work. I did leave the spade on and went for a pee break and it did some work blowing out loose dirt but you really need to actively grind to work faster. Stab, blow, and remove loose dirt are the repeated actions.
Here's a small video from the excavation end.
Notice how the angle of attack is lower as you dig out the entrance.
I use gloves even though it's low pressure because the venturi might rip skin back and I normally have skin tears on my hands. I've seen the video of compressors ripping skin back to the elbows, not worth the risk.
I use a prodding motion and alternate working both sides.
The gravel spoil on this photo came from the middle.
Last task is to feed the pipe through the hole. I tape the pipe to the air spade and shove it through.
Thanks for reading my how to/ hoe to guide to air excavating.
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