Loads on Buried Pipe 2

[random_engineer]

I am designing a small structural steel access platform for an industrial facility. The structure is supported by a 2' thick soil supported mat foundation (25'L x 10'W); bearing pressure due to D + L is approximately 500psf, and maximum bearing pressure due to D + W is 1200psf.

Here is the kicker: there is an existing 20" diameter steel pipe directly under the proposed structure and foundation. The pipe is carrying cooling water and is critical to plant operation. However, the pipe is buried relatively deeply, and I have approximately 10ft of fill between the top of the pipe and the bottom of the new foundation.

Given the depth of the existing pipe, can the loads from the new structure and foundation acting on the pipe be neglected? I know that AASHTO allows vehicular live loads to be neglected on buried culverts when fill depth exceeds 8ft, but am unaware of any guidelines for buried piping. Moving the structure is not an option, and before I look at more expensive options (i.e. piles), I'd like to hear some opinions from other engineers. Thanks in advance!

 

[JedClampett]

Get a copy of AWWA M11. I don't want to spoil the ending for you, but you're going to find that your pipe is OK.

 

[HTURKAK]

If maximum bearing pressure due to D + W is 1200psf. that makes 8.33 psi. That is , still less than H 20 highway load. If the fill is approximately 10ft between the top of the pipe and the bottom of the new foundation, can be neglected.

But , I think it will be a good practice to analize the stresses developing at buried steel pipe. You may look to the following doc.s for reference .

- ASCE Manuals and Reports on Engineering Practice No. 119 Buried Flexible Steel Pipe Design and Structural Analysis.

- AWWA MANUAL M11 Steel Pipe- A Guide for Design and Installation

Or you may look the following doc. is free ALA Guidelines for the design Buried Steel Pipe


The following fig. from the same doc.

PS . My personnel preference would be moving the footing or pipeline and avoid interface for future maintenance or , install the cooling pipe in a sleeve pipe under the footing..

 

[AskTooMuch]

You're fine. Your structure is just a small access platform like you said. There are excels and tools for this like pipeline toolbox but you will need the pipe specs and loads (operaring pressure, etc..) to check the pipe.
Look at it this way, the maximum soil bearing pressure at the bottom of your foundation is say 2000psf. 10' below that would not affect the pipe.

I dont recommend installing sleeve to existing pipe. This is 10' deep, imagine the digging they have to do.

 

[HTURKAK]

You are right.. i looked to the thread.. The pipe is existing 20" diameter steel pipe. Sleeve could be an option for new construction.

 

[random_engineer]

Thanks for the insight. Much appreciated!

 

[dik]

They have to determine which end to sleeve it from, too.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik