Tall reinforced concrete retaining wall.

[derecha1]

I have a situation where we are designing retaining walls that are 25-30 feet high that are being used as dividers for a 4 bay fuseplug spillway on a dam. The walls act as retaining walls in the scenario that if one of the bays actually fails (in a large spill event) leaving one side to retain soil. So that compaction of clay cutoffs in the fuse plug can be achieved, we are being required by our state Dam Safety division to put a 1:10 taper on both sides of the walls. This makes the wall rather wide at the base (Up to 6 feet). Instead of using concrete for the full 6-foot base and tapering as we go up, has anyone used inexpensive and easy to place filler materials to reduce the amount of concrete in the circumstance?

Any help would be appreciated.

 

[Focht3]

Hmmm,

I understand the cost issue. But let's think about this a bit. You have three four issues to consider:[ol][li]Constructibility.[/li][li]Strength.[/li][li]Cost.[/li][li]Liability.[/li][/ol]By inserting "filler" into a tapered section, you have a real construction headache. The use of a filler will reduce the strength of the section - strength that may be needed in a catastrophic event. The reduction in material cost may well be consumed by additional labor and schedule costs. And where will the liability rest for weakening the strength of critical elements that may be needed during a dam failure? Remember that dams are designed for 'high safety' and a 100 year service life. This isn't a commercial office building that may be torn down in 25 years -


For me, that sounds like a lose/lose situation. If the owner wants to push the issue with your state Dam Safety division, let them. But I'm willing to bet it won't fly -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[derecha1]

I definitely want the walls to be strong and will not sacrifice durability and strength for cost savings. The main reason for considering this is that the walls do not need to be 6 feet wide at the base structurally. This is only based on the 1:10 taper for compaction against the walls.

I really didn't have a feel for whether this is done (using a filler such as geofoam) regularly or if it is silly and you end up replacing cost in labor over material.

I appreciate your input.

 

[SlideRuleEra]

Concur with Foch3.

For many projects, concrete is considered by many to be "the" material of choice for the following reasons:
1. Made for relatively low cost, common materials.
2. Good availability many places.
3. Familiar to construction work forces (and regulators as mentioned).
4. Material properties are well understood.
5. Proven environmental longevity.

Try to keep things simple when possible. Anyway much of your cost would be for formwork that would probably be indentical whether you use monolithic concrete or a concrete - (something else) composite.

Best Wishes

 

[Focht3]

We recently looked at geofoam to replace flowable fill in a decidedly "low tech" fill problem. It turns out the geofoam is nearly $50/CY in place after labor, shipping, etc. We didn't see a cost advantage over flowable fill, with greater risk. We dropped geofoam from our list of permissible fixes (in consultation with the owner and specialty contractor) as a result.

As [blue]SlideRuleEra[/blue] implied - follow the "KISS" principle.



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[letrab]

derecha1,
Instead of placing void formers within your section to minimise the amount of concrete used, it may be cheaper to use plums or low stremgth concrete in the central section.
An additional benefit of using a really lean mix in the central section would be to minimise heat gain during hydration.
The normal strength concrete would only be required on the outside for durability and strength purposes and can be placed at the same time as the lean concrete.

 

[Focht3]

Hmmm,

But you still have set up and strip forms twice. And if the filler is 10 feet high (for a 25 ft tall wall), the bracing issue will be significant.

Pour it solid - and forget it.



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[derecha1]

I appreciate all of your advise and consideration. I think that answer is just go with concrete. I just wanted to see if there was anything else out there.

Thanks both for all of your help.

 

[BigH]

If they want it so - let it be. This is not a "commercial" project - but an important civil work - the extra concrete is not likely that much in the overall picture. If permitted, you might use rubble concrete - that is by judiciously placing riprap size stone (say 300x300x300mm) within the concrete. Normally, in this, though, there are restrictions about proximity of stones with each other and to outer surfaces.