Placing retaining wall in lifts?

[SteelPE]

I have a project with a retaining wall that is approximately 13’ tall. Due to some so constraints onsite the contractor needs to place this wall in lifts and is asking if this is OK. The wall is 14" thick and has an inner and outer layer of steel. Both layers are designed as if the wall was a cantilever wall (outer layer) or propped at the top (inner layer).

The only downside I can think of has to deal with the shear transfer through the cold joint between concrete lifts. Here we could intentionally roughen the surface and then provide additional reinforcing at the joint (the dreaded shear friction). Are there any other downsides?

I can’t believe I have never run into this before.

 

[ztengguy]

Have them form a shear key at the top of the first pour, a simple 2x4 usually suffices.

I bet this happens more than you know, the contractor just doenst call about it

 

[SteelPE]

I would like to think I would see a big joint in the wall when I visited the site however, this contractor has called about everything.

 

[SlideRuleEra]

I concur with ztengguy. A proper horizontal construction joint at mid-height is really not any different than the joint between the top of a wall's foundation slab and the bottom of the wall itself... and that's done often.

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[SteelPE]

SlideRuleEra, that is a good way of looking at it, but I do have reinforcing bars through the joint of the footing to the wall to help with the shear transfer.

 

[jayrod12]

I would hope you have reinforcement running continuous across the cold joint if you put it at mid-height as well. So I'd be fine with it.

 

[SteelPE]

Jayrod, we would have bars that were designed to resist the bending forces running through the joint, not specifically bars designated for shear reinforcing.

 

[jayrod12]

You think they wouldn't pull double duty? They'll resist the bending stresses but not the shear?

Do you ever consider a combined action of axial and shear in any steel section? No, you check each individually, provided it passes both checks on it's own we consider it adequate. How is reinforcing steel any different?

 

[KootK]

The bars absolutely can pull double duty in this application. As long as the rebar is developed on each side of each lift, you can use shear friction and forgo the key (maybe even the roughening). Many engineers will, of course, include the key as well. Belt and suspenders.

In my opinion. Most walls should be designed to accommodate multi-lift pours. It's common and not something that you want to be vetoing.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[DamsInc]

Don't know your application, but from a durability/serviceability standpoint, are you retaining a significant amount of water? If so, consider placing a waterstop at the joint.

 

[CELinOttawa]

Jayrod: This has been discussed before, but I am one of the engineers who do consider combined actions in Steel sections. So should all EU engineers, NZS engineers, Canadian engineers, and just about all of the codes I've seen aside from the US codes...

Just saying. I do agree, however, that this case should be fine.

 

[SteelPE]

I understand that the bars can pull "double duty" especially since both faces have sufficient reinforcing for both the cantilever case and propped case. However, should I be a bit nervous with the fact that the cover for the bars is only 2" as they are cast against a formed surface?

I haven't talked to the contractor since our original conversation. I'm not sure what he is planning to do as he was in talks with a shoring contractor to stabilize some of the existing grade. Last we spoke I told him that we could probably do something to accommodate his request. I just wanted to make sure I wasn't forgetting anything.

 

[KootK]

What bothers you about the cover SteelPE? The best place for shear friction reinforcement is in the flexural tension zone.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[CELinOttawa]

I think you're worrying about nothing wrt the cover - 2" is hardly an "only" cover... 1" and less is found in older structures all the time!

 

[msquared48]

I think I would also consider a PVC water-stop across the joint too.

Mike McCann, PE, SE (WA)