Max reinforced concrete pipe slopes 1

[evett]

Dose anyone know of a publication or guideline that lists the maximum allowable slope to be used for various sizes of reinforced concrete pipe? Taking construct ability into consideration as well as durability of the pipe.

 

[RWF7437]

As far as I know, you can set RC pipe vertical if you want to.

 

[TEVETT]

I was instructed by a DOT not to exceed a 10% grade for 48” pipe and 15% grade for 24” pipe. The person who instructed me to do this told me that it was a construction issue.
Is that true?

 

[RWF7437]

I'm sure it is true than someone at DOT told you this. I'm also almost sure that these maximum grades are arbitrary. If you could not set 48-inch RC pipe vertical you wouldn't be able to build the millions of manholes that exist in the world. Probably billions ?

Setting large pipes on steep slopes is difficult and possibly dangerous. It also may increase erosion of the pipe and earth at the outlet. On steep slopes it might also be necessary to cast anchors around the pipe to prevent separation as the backfill settles. The DOT may have test data to justify their maximum slopes. You might ask to see it in order to make your own informed judgement.

 

[Maury]

I've been told (by highway people) to limit storm sewer flow velocity to a maximum of 10 fps to prevent abrasion of the bottom of the pipe. I've also designed systems that exceed this velocity, with catch basins to try to collect the sand and gravel before it gets to the pipe.

Maury

 

[xghalibx]

I don't see high velocity being a problem in conc. pipes as long as erosion control is addressed at the outfall and HGL is kept in check (below the rim for, say 100-year event).

 

[LHA]

While references abound with general guidelines such as the following, I do not know of one which makes a definitive statement.

The previously stated 10fps is a good conservative limit for sanitary sewer flow, due to expected continuous flow of high-solids liquid. Storm sewer flow is expected to be intermittent; although sand and grit are a concern, I usually try to limit velocity to 15fps (and have gone over 15, and had it approved) over shorter runs, 12 on longer runs in RCP. An ADS salesman once told me his engineers say HDPE pipe is good to periodic 25 fps, but I would never design to that. I should note that he was unable to provide literature backing the 25fps. ADS does provide literature showing negligible abrasion wear at 15fps with "fine sand", but measureable wear with "coarse sand"...but these tests are with very frequent cycling, which is not to be realistically expected within storm sewer pipes.

I know I didn't really answer the question, but it is a question I often have, so thanks for the motivation to summarize to myself!

 

[cvg]

Los Angeles County (and the American Public Works Association) have standard details for pipe anchors and backfill stabilizers for concrete pipes to be installed in trenches on slopes as steep as 1:1