Buried Culvert Pipe

[Everynameistaken]

Hi Civil Guys,

I have a question regarding designing a CSP culvert for a haul road.

When I am calculating the allowable buckling pressure I need to include an impact factor for the vehicle which increases the load depending on the burial depth, this would be considered pretty standard I think.

When I am using the Iowa deflection formula to calculate the deflection do I need to consider this impact factor?

Typically in above ground structure, the deflection would be calculated without any impact factor and the ultimate limit state would be designed based on impact factor with load factor or factor of safety as well.

Thanks

 

[SlideRuleEra]

For a product as widely used as corrugated steel pipe, I would not second guess the manufacturers by performing calculations. Manufacturers publish proven information on their products that includes many factors. Contech, for example, has a Design Guide, expect other suppliers do the same. Recommended cover for various loading conditions begins on page 7. Heavy construction loading, such as a haul road, is addressed on page 15.

Also, may want to see what the National Corrugated Steel Pipe Association has to offer.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Everynameistaken]

Hi,

Thanks for this info.

When I look at the heavy equipment items it looks like it is based on a temporary condition. Basically just add a bunch more fill (of whatever type) over your finished grade and then pull it off when complete?

I am looking at final condition where the vehicle will use the road for the next 20-30 years. The fill around the pipe and above the pipe and in the road will all be controlled fill that is placed as we like with 95% SPDD etc. so the filling conditions are the same as under a highway.

The construction equipment section has the same minimum depths for any pipe ranging from 12" to 42", this seems to be a pretty large range for the same fill height!

I am looking to try and have a design based some rational codified approach or simple first principals (like the Iowa) so I can try and learn and understand a little more what is happening with the pipe itself. I think the tables are pretty straight forward for highway or rail vehicles and are based on this type of approach as best I can tell, but I'm not so convinced about the heavy construction equipment section.

 

[oldestguy]

You are missing the point. I'd bet the manufacturer has take many factors into account and don't forget those pipes on most roads have been subjected to many a vehicles carrying a lot of earth, etc. during construction and likely at much lower cover than you will use. If you have the time to play with this, fine, but don't exceed what the manufacturer provides. If you really are concerned about over loading, I'd place a temporary plank roadway over the required cover, using hardwood at least 3 inches thick and extending beyond the 45 degree plane up from the lower sides of the pipe. In some circumstances we use compressible fill right on top of the pipe. Do a Google search for Spangler and his "imperfect trench Design". I've used it when an existing pipe could not be taken out of service for the adding of 15 feet of fill above it. My compressible fill was leaves from municipal street sweepings.

 

[oldestguy]

Spangler is long dead from Iowa State University and doesn't show with my search but several writers have papers on this subject.

http://ascelibrary.org/doi/10.1061/(ASCE)1090-0241(2007)133:3(277)

Hell, combine this with planks and you have both suspenders and a belt job there.

Another source.

http://link.springer.com/article/10.1007/s10706-012-9608-0?no-access=true

 

[SlideRuleEra]

Everynameistaken - See "The Iowa Formula, What It Is - And Is Not". A buried flexible pipe, like CSP, cannot accurately be analyzed by itself. The soil and the pipe interact; each contributes to the buried pipe's performance. There is no simple solution.

Since you are interested in the details, go to this Link, take a short survey, and download the NCSPA Steel Pipe Design Manual. See Chapter 7, Structural Design (Pages 369-445). The complex information there will probably convince you that using published tables is not a bad way proceed.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net