Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.


Cover for a reinforced concrete pipe culvert

Cover for a reinforced concrete pipe culvert

Hi all. I am specifying a 18" reinforced concrete pipe culvert under a road with HS 20 loading. The pipe is barely under the base and there is no sub-base. In other words, the pipe is right below the base, with minimum thickness above the top of pipe. Is there a requirement for a minimum "cover" or distance before we could put the base above the pipe? The thickness of wear course is 3", base is 8". Thank you in advance.

RE: Cover for a reinforced concrete pipe culvert

The American Concrete Pipe Association has information that will help. See "Design Data 1 - Highway Live Loads On Concrete Pipe" (free .pdf download) at this link

Also, you may want to download the "Concrete Pipe Design Manual" at this link (see Chapter 4)

Finally, if it turns out that you do need more cover, perhaps an equivalent elliptical shaped pipe can be substituted for the 18" circular RCP. idea

RE: Cover for a reinforced concrete pipe culvert

All tables available, that I am aware of, assume 1-foot of cover to the sub-grade.  These tables identify .01 crack for a concrete pipe vs pipe classification.  The loading on the pipe can be manually computed and then the required classification can be identified.  These procedures are availble in the Concrete Pipe Design Manual.  Check out for information.  I set up a spreadsheet to automate the procedure.

Good Luck & Have Fun!

RE: Cover for a reinforced concrete pipe culvert

The only way that will work as a long term solution is to place concrete all around the culvert.  I don't care how well compacted the base is on either side, within 1 or 2 months at best, there will be a nice speed control device there.

BigInchworm-born in the trenches.

RE: Cover for a reinforced concrete pipe culvert

Seems like a pretty small pipe.  I wouldn't be as worried about the pipe as the road.  As BigInch says it is probably best to lay it in concrete.  I would also look at adding some subbase next to the concrete so that if you have movement it is spread further.

RE: Cover for a reinforced concrete pipe culvert

If you plan on using concrete encasement, remember that over time the subgrade next to the concrete will compress creating a little depression and mound of asphalt.

RE: Cover for a reinforced concrete pipe culvert

Right, It won't do to have a square bump in the road either.  I wasn't clear.  I meant to say make a ramp up of the concrete in the subgrade until its even with the top of the pipe.  

BigInchworm-born in the trenches.

RE: Cover for a reinforced concrete pipe culvert

Also, it would be wise to specify a greater strength class of concrete pipe since the cover is so shallow.  Class III pipe is 'standard' RCP, while Class V would be the highest strength class for pipe before a custom pipe design is required.

RE: Cover for a reinforced concrete pipe culvert

You probably already considered this, but can you raise the profile for more cover?

     "...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close