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Outlet pipe sizes in retaining walls

Outlet pipe sizes in retaining walls

Outlet pipe sizes in retaining walls

(OP)
I have a 14' tall granite rubble wall that I've designed and on site there is a 60" outlet pipe they want to run through the wall. I'm not sure how that would work. I think that at the location of the pipe there is no soil so there is some help there but that's a pretty big hole, almost half the height of the entire wall. I'm thinking about placing reinforcing around the hole and also providing a concrete collar around the pipe. Are there any guidelines on max sizes for holes in walls like this?

RE: Outlet pipe sizes in retaining walls

Did you mean 6' or 60'?

No guidelines that I'm aware of - just engineering principles.
Your idea of a concrete collar to protect the pipe from shifts in the rubble wall and crushing pressures sounds appropriate.

Design the concrete donut to take vertical crushing force from the weight of the rubble above it.

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RE: Outlet pipe sizes in retaining walls

(OP)
I meant 60" so 5'. I totally did not proofread before posting that. Thanks for your response though!

RE: Outlet pipe sizes in retaining walls

The FHWA has a manual on rockery walls, don't recall if it has any info on pipe openings. If you can't find it on line I'll post a link later when I get home tonight.

RE: Outlet pipe sizes in retaining walls

I can't add anything other than JAE needs glasses and jplay does not need to apologize as it say 60" :>

RE: Outlet pipe sizes in retaining walls

If you look carefully jplay edited his post. The original said 60 feet...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Outlet pipe sizes in retaining walls

Buster's reference: Link. Generally great but doesn't speak to this. How big and rectangular is your rubble? Is it even right to think of it as rockery? Any positive tieback into the retained soil?

I don't envy you this problem. Feels like you're heading for cowboy judgment territory. I'd recommend placing a call to somebody who manufactures related product like redi-rock. One would think that their engineering department has dealt with this before. When is picture

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Outlet pipe sizes in retaining walls

(OP)
It's definitely rockery, they are using a granite rubble wall so it won't be a segmental wall but granite blocks mortarted together. It's about 120" wide at the bottom and 18" wide at the top, front batter. We're not providing any geogrid, the original design was a basket wall with geogrid and it failed and left ripped away from the geogrid so they are requesting a gravity wall. I would have preferred a concrete cantilever wall but sometimes you have to provide what they ask for. The wall is about 120 feet long and we're at 40-50 feet mark along the length. I'm trying to get the elevation of the pipe to determine if it's near the top or bottom (yes this should be on the friggin plan but the plan stated 24" pipe so clearly it's not up to date haha)

JAE was definitely correct I said an impossible 60' in the original post :(

RE: Outlet pipe sizes in retaining walls

If this pipe will eventually carry water with much of the full area used, there should be a design with details needed for headwalls at outfalls, such as cutoff rings to prevent seepage erosion alongside the pipe, erosion protection outside of outlet, etc.

RE: Outlet pipe sizes in retaining walls

A diagram or sketch would help here a lot, especially X section, but I'm not sure what exactly your concern is?

The pipe (small tunnel) is hopefully man enough for the over burden pressure but in terms of the wall it just replaces some of the stones.. If it was a hole that needed support then that's a different matter, but I'm having a little difficulty understanding the wall and its cross section.

Is this a 90 degree triangle wall or an equilateral triangle wall?

Could you use gabions behind the front surface to give you more stability?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Outlet pipe sizes in retaining walls

Thanks for posting the link KootK

RE: Outlet pipe sizes in retaining walls

I would be very careful about settlement behind the rockery which could cause the pipe to leak with almost certain catastrophic result. Perhaps the concrete encasement should extend a lot farther.

I think you need to consider a cutoff wall to handle underseepage and I am wondering how you intend to keep the rock on top of the pipe from sliding off. Given all that, perhaps a 14 foot high headwall with a cutoff wall and apron would be a better idea.

RE: Outlet pipe sizes in retaining walls

OK, so this isn't really a rockery or a "rubble" wall, but a weak concrete wall with lots of big rocks in it - " granite blocks mortared together". Correct?

I can't see a pipe causing any really issues other than being a potential leak path and lack of friction for the rock mortar wall.

A few plates or bars welded on ( if it's metal) or rouging up the concrete it it's concrete to get a good key would seem like a good idea.

Can only assume this large pipe won't have any expansion or thrust / movement?? That could bring down your wall.

If it's a thin steel pipe then check the overload capacity, but if it's buried in soil coming into the wall it's almost certainly OK.

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Also: If you get a response it's polite to respond to it.

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