Saw some thing that scared me the other day. Driving past a pile of odd shaped reinforced concrete pipe, i asked the guy i'm working with what was wrong with that pipe, and he said it was "D" pipe.
I had no idea something like that even existed. What is even more worrying is how many times i may have run across that measuring inverts and not recognized it.
The glimpse you get while measuring inverts is a cross-section at an acute angle and often the flowline will be loaded, to some extent, with sediment and debris.
How often is this type of pipe used? If i did manage to recognize this type of pipe, what type of measurements are required to define it?
Are you referring to:
Arch (ASTM C-506) or Elliptical (ASTM C-507)?
Been around quite a while I believe.
Loyal
Not Often
"D" pipe is 2-3 times the cost of equivalent capacity round pipe so it is used only when absolutely neccessary.
Like you need to maximize flow through a single pipe and are limited in invert and cover elevations. It is very high capacity. A pipe carries the most water at about 75% flow height. With the almost square bottom half one can see the capacity advantage with "D" pipe.
Enviromental concerns could require "D" pipe, like you had to expedite turtles crossing underneath the roadway. Turtles can walk on the flat bottom easier than on a round bottom.
Large "D" pipes can be used for pedestrian access, such as to the infield on a race track. Even larger "D" pipe can be used for vehicle access.
Generally in a capacity/height clash elliptical concrete pipe is used. Most typically as horizontal elliptical pipe, wider than high. I had one instance were I had to redesign a storm sewer with vertical elliptical pipe. Same pipe just set higher than wide. Contractors were excavating for a storm sewer installation cross an in town street. Excavator cut one of the first fiber optic lines in the US. The markout was wrong and AT&T engineers were on site. Contractor did not pay the oodles of dollars for repair. Because of encasement requirements on adjoining utilities, fiber optic and other I redesigned the storm sewer with Vertical Elliptical RCP to manitain capacity and get through the tight area.
"D" (Arch) pipe and elliptical pipe can be had in RCP and corrugated metal. I have yet to see either style in high density polyethelene.
When in doubt just report what you can measure, 24" high (not diameter) concrete pipe. For others report the height (rise) first and then the width (span). 14"x23" HERCP is equivalent to 18" diam. RCP. 11"x18" arch is equivalent to 15" diam. RCP. Those are the smallest typical sizes. As a comparison 13"x22" arch is equivalent to an 18" RCP and smaller in both dimensions than the equivalent HERCP but more expensive.
Often times horizontal elliptical pipe is used rather than round because the wider width can lessen the riprap area size at the discharge point.
Paul in PA, PE, PLS
This may help you when trying to figure out what size pipe you're dealing with.
http://www.rinkerpipe.com/TechnicalInformation/drawings/PDF/009.pdf
http://www.rinkerpipe.com/TechnicalInformation/drawings/PDF/008.pdf
Corey
Not Often
Paul in PA, Corey, Loyal, Thank You.
