Downspout drain under sidewalk

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Divepro99
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Downspout drain under sidewalk

Post by Divepro99 » September 4th, 2019, 8:01 pm

Good evening,

Recently bought a house with downspouts hitting splash blocks, which I am routing to drain pipes. (Yes, this project is not fun or glamorous, but it is needed.)

For the current downspout, I need to go beneath a 36 inch wide sidewalk using a water drill. In fact, this location will have a French drain pipe (https://www.lowes.com/pd/Charlotte-Pipe ... pe/3362194) beside the downspout pipe, as the location experiences a lot of run enough from a slope. The trench will also be filled with gravel, wrapped in landscape fabric.

The trench beneath the sidewalk is about 9 inches wide, 5 inches deep. Should I use thin walled pvc (https://www.lowes.com/pd/4-in-x-10-ft-S ... pe/3133147) or schedule 40 pipe? Both would be packed with as much gravel as possible (wrapped in fabric) and dirt outside of the fabric.

Schedule 40 seems like overkill, but it won’t flex or bulge al all. I don’t want the concrete to crack as it’s only three inches thick. The heaviest thing the sidewalk might experience is a riding mower.

Thanks.

schreibdave
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Re: Downspout drain under sidewalk

Post by schreibdave » September 5th, 2019, 6:20 am

If you are concerned about supporting the sidewalk above I would think you would want to use the sturdiest of your options. When I ran my downspout under the sidewalk I used 4" black corrugated flexible stuff. The top of the pipe is in contact with the bottom of the sidewalk. However my sidewalk is free floating 3' x 2' slabs. They have the freedom to move a little bit. But I have not noticed that slab sinking at all.

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HoosierLawnGnome
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Re: Downspout drain under sidewalk

Post by HoosierLawnGnome » September 5th, 2019, 12:26 pm

I would go schedule 40. I've had the black, corrugated pipe collapse and it cant be rotorooted. Too weak and it tears it up.

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Re: Downspout drain under sidewalk

Post by northeastlawn » September 5th, 2019, 8:18 pm

As an engineer, you are much better just cutting the sidewalk square and repairing it. For a sidewalk project we would saw cut a square out, lay the pipe, back fill and compact it, then repour the square w/expansion joints.

I am not sure what a water drill is, but if your using water to jet out a hole under the side walk....you will never be able to stuff enough material over the pipe to support the sidewalk w/o having some voids. Cracks will come from the voids causing the sidewalk to settle.

In construction they sometimes jack utility pipes, where they hammer a larger pipe under the road. Someone then shovels out the dirt in the pipe as it is jacked under the road. Once the larger pipe is across the street, the utility pipe is slid into the larger pipe. That way there is no voids to cause the road to settle.

I only bring up the above up because using two pipes is how they ensure there are no voids.

You might be able to mix some loose concrete (we call it flowable fill) and stuff in the hole and over the pipe. That might take care of the voids, but never seen that done for a small project.

Like I said its almost easier just repouring a new concrete sidewalk square.

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Re: Downspout drain under sidewalk

Post by deboy922 » September 6th, 2019, 2:36 pm

About 3 years ago in the spring when the ground was soft, I used a sledgehammer to dive 3" schedule 40 pvc (not perforated) under my sidewalk to connect to a downspout. It was work; but it has performed well; and the sidewalk has not cracked. I cut the end of the pvc to make a point. I drove the pvc in about 6" and then would pull out the pvc to remove the dirt core and repeat. I went about 6" under the sidewalk to get under the sidewalk and most of the pea gravel. I was scared to use water to drill, as I did not want to erode a lot of dirt and pea gravel under the sidewalk.


Divepro99
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Re: Downspout drain under sidewalk

Post by Divepro99 » September 6th, 2019, 3:31 pm

Thank you for your input.

I, too, am an engineer (nuclear and mechanical), so I tend to be conservative on many projects. However, it’s been 25 years since I learned anything about concrete- especially, a thinly placed 40-foot long, sidewalk (with a questionable base).

I ended up using 220 Schedule 40 PVC (not foam core schedule 40). Yes, I had to drill holes into one pipe, making it into a French drain line. I packed the cavity full of gravel on the bottom and sides and used CLSM on top of the piping (outside of the landscape fabric) until the cavity beneath the sidewalk was full. The piping was vibrated during the CLAM placement.

If the sidewalk cracks, I will cut and replace that section, which will look odd given that the sidewalk is 30 years old and continuous with cut every 5 feet.

Here is the water drill kit that I have used several times to “tunnel” beneath a sidewalk.
https://www.amazon.com/Orbit-Sprinkler- ... ay&sr=8-40

Thanks and have a great weekend.

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Re: Downspout drain under sidewalk

Post by northeastlawn » September 6th, 2019, 3:46 pm

Sounds like pipe jacking at a smaller scale. I can see how it would work,

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