Steel Casing Thickness

[esass13]

We have plenty of standard casing size and thickness requirements for bore and jack, but we are installing some steel casing for gravity sewer under creeks, etc. via open cut. The install will be pretty shallow from a few feet of cover to the crown exposed. My question is, what casing thickness do I need for a 42" or 48" steel casing? I don't think we need to pay for the extra thickness we'd need for bore and jack, but what is thick enough for open cut so that the casing is not "flimsy" (sorry for the non-technical jargon). The casing in the open cut is just to protect the PVC pipe.
Thanks

 

[fel3]

In most situations, an open cut casing pipe would be designed to support the soil and traffic loads above it. For steel, that would be a flexible pipe design. However, here you may not have any traffic loads except during construction--and your likely construction equipment should have lower ground pressures than road vehicles--but you might have potential lateral loads if creek washout is an issue.

Here is a link to two Mathcad prime 3.0 worksheets that I posted on the PTC forums in 2014 for flexible pipe design for vertical loads:

https://community.ptc.com/t5/PTC-Mathcad/Lusk-Flexible-Pipe-Design-zip/m-p/449427

The .zip file includes a .pdf version of each worksheet in case you don't have Mathcad.

If washout is a possibility, then you may need some sort of concrete encasement, but what that looks like would be very site specific and I would want input from the geotechnical engineer and possibly a structural engineer. I have only had to do this once and it was about 30 years ago, so the details are a bit fuzzy.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[bimr]

Most municipal agencies have standard sizes for sewer casing. The amount of money that you may save by installing thinner casing will be a very small fraction of the construction project.

 

[fel3]

bimr...

Around here (central California), I don't know of any agencies that provide standard sizes for casing pipes, whether for open cut or for jack and bore. The few times I have done open cut casings, I had to calc the wall thickness myself. I even did an open cut casing for a 12" water pipe that was going to go under a road being relocated by Caltrans (casing went first, then road, then my water pipe) and Caltrans had nothing. Maybe they do now, but in the early 1990s they didn't.

Fred

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[bimr]

Around here (central California), I don't know of any agencies that provide standard sizes for casing pipes, whether for open cut or for jack and bore. The few times I have done open cut casings, I had to calc the wall thickness myself. I even did an open cut casing for a 12" water pipe that was going to go under a road being relocated by Caltrans (casing went first, then road, then my water pipe) and Caltrans had nothing. Maybe they do now, but in the early 1990s they didn't.

The point that I was making is that there is not much savings in trying to skimp on the wall thickness of a casing.

There are many utilities that have stand details on casings. Here is an example:

Standard Details

 

[fel3]

bimr...

I agree that it's not worth saving a few pennies by optimizing the casing wall thickness. My point was that the agencies around here that I have dealt with don't have a detail like you show. Perhaps it's because they rarely need open cut casings.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[nackra]

check source for casing pipe:

http://www.steel-pipe.com/ansi_pipe_chart.htm

I agree with bimr and fel3, use standard material (not custom)

 

[esass13]

Thanks for all the replies.