RCP - Placing rock or grouted stone directly on top of a pipe

sure you can do it, but it may or may not be a good idea. you haven't given much information to go on. what size pipe, what size and type of rock, why not a headwall, any flared end section, in a basin or a ditch, levee or dam, highway? what is the anticipated design life?

If you design for it, you can do it. It's a question of whether the numbers work. Depending on how the loading is applied and what you normally assume, you may have to modify your design methods.

What is the in-place density of your material? Is this just flowable fill?

Richard A. Cornelius, P.E.

CWEngineer said:

...reference that prohibits placing rock or grouted stone directly on top of an RCP?

Click to expand...

The American Concrete Pipe Association's Concrete Pipe Design Manual specifies soil that is recommended for pipe overfill, rocks are not included:

When you put "rocks" on top of a pipe and compact the rocks, the rocks tend to punch holes in the pipe.

Richard A. Cornelius, P.E.

type 1 "gravelly sand" will have a significant number of rocks and per UCS, "gravel" can be up to 3 inch. are your rocks this big? encasement fill with concrete is done all the time. depending on your specs, "grouted rock" could be classified as "concrete". for culvert outfalls, embedment in rock (gravel or cobbles) is not that uncommon. I would not recommend trying to compact it.

The pipes could range from 18 in. to 96 in. or so, rock could vary from 6in. to 24 in. These particular pipes are being placed within a levee, with a headwall where they connect to an outlet structure. The fill will be engineered fill.

I am assuming that if rocks are allowed, they need to be hand placed, to avoid damaging the pipes (in lieu of dropping them with a dozer). And that they will not be compacted.

Another, issue if placing rocks or grouted stone is allowed to be placed on top of the pipes, is that if we need 2 feet of fill (soil), so that soil arch defects do not develop and not void the D-Load calculation/application the RCPs are designed for?

Thanks

minimum cover of 2 feet is intended mainly to reduce live loads. it also helps to anchor the pipe from moving. I dont understand why you would place rock on the pipe if you have a headwall

I guess I would not use "rocks" anywhere near the pipe. Only use these "rocks' in the top 3 feet of the levee. I would expect the levee to be a well compacted earthen structure.

Richard A. Cornelius, P.E.

Actually, it is for a channel slope, not a levee. There are dimension constraints since the length of the slope is not that long, that is why the discussion of placing rock or grouted stone on top of the pipe have came up.

"rock could vary from 6in. to 24 in." "they need to be hand placed, to avoid damaging the pipes (in lieu of dropping them with a dozer). And that they will not be compacted" ~Really?? every single one? Do the contractors wash each rock down and polish it as well?
A 24" rock is going to take two or three men to "hand place" it.

There is zero chance of this happening in reality. Apart from anything else, there will be added weight and point loads being added to something which doesn't like point loads. Concrete pipe is great stuff, but start even a small crack going through it down to the re-bar and 10-15 years down the track - failure.

This is a wholly bad idea.

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