# How we dig a 12 ft deep hole



## Cuda (Mar 16, 2009)

Here are some pics of how we dig a 12 ft deep hole for a pipe burst with other utilities (electric, fiber) in our path. You can't use a power tool within 2 feet of either side of a painted utility so that throws out using an excavator but the job still has to be done right? In these pics we use a large compressor with an air knife and a crane to pull up the soft soil after the air knife has made it puffy. It's slow but not tiresome to do. We build or shoring as we drop farther and farther down. This job is a little more crazy than some because the soil in sandy with rock which is very unstable. The crane is what makes it seem like no big deal at the end of the day.


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## ChrisConnor (Dec 31, 2009)

So, the air knife cuts the soil, and you just bail it with buckets? What's the dust crosswind like?


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## fixitright (Jan 5, 2012)

Your posts are always great.

We have this frozen ground thing here.
Wonder how it would work?


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## chonkie (Jul 31, 2014)

5th pic isn't showing up for me. I'm wondering if it's a pic of the air knife.


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## Plumber (Jan 18, 2009)

chonkie said:


> 5th pic isn't showing up for me. I'm wondering if it's a pic of the air knife.


Kinda. It's a Ditch Witch unit. The "air knife" part is confusing. I wonder if its a rental.......................................


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## rwh (Dec 17, 2014)

Why are building drains so deep there? I'm a flatlander. Ours are deep enough not to freeze. Water table here is high. That deep hole would be difficult to keep dry


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## chonkie (Jul 31, 2014)

I've been checking it out on the net, you do work with some neat tools.


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## Cuda (Mar 16, 2009)

Air Knife is a supersonic air gun used in trench rescue, utility line pot holing, and some tree root preservation. If you hold it in the ground there is not much dirt in the wind but it can blast rocks all over lol. Yea just air knife the soil it turns hard ground into fluffy lite dirt and shovel it into buckets thats why it's not that hard for the guy digging and not hard for the guy on the crane duty. You do have to wear a full sandblaster helmet if you dont want dirt in your hair and down your back lol. If the ground is super hard we switch over to air chipping hammers with spades and work a little bit harder. I will get some pics of the air knifes tomorrow we use 2 at the same time thats why we have such a big compressor 375 cfm.


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## Cuda (Mar 16, 2009)

rwh said:


> Why are building drains so deep there? I'm a flatlander. Ours are deep enough not to freeze. Water table here is high. That deep hole would be difficult to keep dry


Sometimes the water table is higher than the sewer and we let hydraulic pumps just run the whole time. Hydraulic pumps are cooled by the hydraulic oil so they can run dry.


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## rwh (Dec 17, 2014)

I should have did sewer. Why are they so deep?


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## rwh (Dec 17, 2014)

rwh said:


> I should have did sewer. Why are they so deep?



Said not did


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## Cuda (Mar 16, 2009)

rwh said:


> I should have did sewer. Why are they so deep?


This house is built into a huge hill so the basement is way below the street grade that's why this one is so deep so close to the house, most of them we do on the peoples property are 6-7 feet as an average, some are 12 footers. Our water lines are only 2 feet deep because we don't have a frost level.


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## Greg755 (Sep 16, 2015)

So how long did it take you to dig that trench with the air knife and what size air knife did you use?


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## Cuda (Mar 16, 2009)

That hole was 2 men, x two 6 hour days
Air knife nozzle size is 175cfm x 2


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## plbgbiz (Aug 27, 2010)

Great idea with the crane Bryce!! We have scenarios like that but have just used the bucket/rope manually. That really wears the guys out.

I'm going to see what my options are for a portable jib that we can get into backyards. We have used the mini-ex on occasion but we can't always get it where we need it.

Thanks for posting this.

BTW: +1 on the sandblasting suit. Our air knife slings quite a cloud of dirt/rocks as well. Sure saves the back aches though.


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## Cuda (Mar 16, 2009)

Here is a picture of an air knife even though it might actually be the other brand that is sold which is called an Air Spade. It has a lot of uses here is a pic of using it under some stairs on the same job, if I didn't have the air knife then we would have broken out the stairs so we could go straight down, the owner and I had an agreement that if the air knife did not work we would break them out at a higher bid and we do a lot of concrete work and will replace up to 3 stairs and any flatwork but since these are irregular and built into a steep grade we would not have been the ones to replace them. Under the stairs is the main sewer stack connection and this exposed it great so we can do our pipe burst. I have not built it yet but we are welding a plate that is connected to another crane of this same size that will attach to our dingo for getting in back yards but it will not have the strength that the trailer unit can do, but 2 buckets is like 100lbs so it will handle that and some more I think.


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## SchmitzPlumbing (May 5, 2014)

whats the advantage to that over hydro excavating? i would rather hydro it but i have never seen it done this way.


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## Cuda (Mar 16, 2009)

Hydro makes the ground into a slurry and here in washington you have to vac it up and take it to a special facility for disposal, a great distance away and higher cost. Then you have to replace the soil with new, more cost. And it makes a heck of a mess on anything but a pothole. When we used our vacuum trailer we only used water if the ground was so hard the air did not cut it. That is the advantage of using water is you crank up 5k psi and it will slice the dirt no problem (well except for I mentioned) Some parts of the country use just air and others use just water. I just got sick of the water and like putting the native soils back in and be done.


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## cjtheplumber (Mar 9, 2012)

Thank you sir for being safe and thank you for the photos:thumbsup:


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## mpm (Nov 16, 2010)

That shoring though....:thumbsup::thumbsup::thumbsup::thumbup:


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## Cuda (Mar 16, 2009)

Here is a little continuation of this job, we pulled a new sewer line in to the 12ft pit and made all the major house connections but there was a downspout line across the driveway and it would have meant another 12 ft hole about 10 feet upstream from the other hole we did, to save the owner money I said I could pull a new line in to our 1st hole after I got inspection on the job and would just backfill and leave 4 ft of hole then put the PD-4 Pow-r mole back in but instead of using it as a cable pipe burster switch it over to a pipe pusher with sonde and the F-5 locator system to create a line 3 feet deep under the driveway. That's the nice thing about the Pow'r Moles is they can do 2 jobs. Anyway we held the new bore between 2 and 3% grade and only had to break a 2x2 foot square to connect the downspout, usually we would pull back HDPE but it was too close to the house and there where wierd issues like some guys had pumped in slurry to raise the driveway and settling foundation that where caused by the bad sewer and downspout line in the first place that I did not want to be responsible for so we made the pilot hole then used the 4" burster head to enlarge the hole then simply by hand pushed PVC back under the driveway.
1st vid is long and upside down at first but it's hard to work and record plus it was raining all day lol





2nd vid much shorter


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