Retaining wall w/o toe and heel

[COEngineeer]

The contractor wants me to design a wall retaining about 8 - 10 ft of soil. Because he doesnt want to deal with frost depth (too close to the neighbor), he wants to use hellical piers underneath the wall instead. Can someone guide me through what I should do first? Can you really do this? You probably need counterfort with hellical pier right?

 

[TDAA]

Design as a wall on piers.

You could contact Atlas Systems Inc. They are a CO local (least in CS) helical installer. They can help with design parameters.

 

[eric1037]

Be careful with helicals. They don't offer much lateral support unless they are fully grouted.

 

[TDAA]

True, but they can also be battered / used as tiebacks.

 

[fattdad]

Helicals can be used as tiebacks if you don't have to worry about the neighbors (which was one of the original design constraints). You'd need alot of helicals to take up the lateral load; however. For an 8 to 10 ft tall wall the biggest design struggle will be the lateral loading, not the vertical "bearing" stress. So you can take up a part of that with embedment (i.e., bringing you closer to frost depth) or let the lateral loads go to closely spaced helical piles.

Good luck, but I think I'd rethink the use of a cantilever retaining wall.

f-d

 

[COEngineeer]

Why would you need frost depth anyway on retaining walls if there is no structure sitting on it? why cant you have only 1 foot of soil on the toe? The project area requires 4 ft of frost depth.

 

[PSlem]

I do it with two rows of helicals, battering the outside. I've posted the book before, Peck, ?, and ? has design guide. I loaned mine out and can't recall other two but someone will.

 

[GeoPaveTraffic]

The book is Foundation Engineering by Peck, Hanson and Thornburn.

As for frost depth, I wouldn't design a wall that didn't go below the frost depth. What happens if an ice lense forms beneath the wall? Just too many potential problems in not founding a structure below the frost depth. Additionally, it is unlikely that the local code offical would allow a wall not founded below the frost depth.

As for using helical anchors, it can be done. It will not be easy but it is possible. In the end, it is probably easier and cheaper to design a standard wall and pay the nearby property owner a little money for a temporary easement.

 

[PEinc]

For a wall 8' - 10' high, why not just design a cantilevered soldier beam wall with either a cast-in-place or precast concrete facing?

 

[TDAA]

Fatdad, tiebacks may be feasible. He really did not say what side is being retained. I was leaving that to his engineering judgement. For all we know, he will be retiaining his side, with fill construction. This could mean that MSE could be better.

There is also the classic gravity wall to be considered. This may still require a deep foundation.

Secant piles may also work for you. There have been some done in CS, and of course T.Rex in Denver probably got a volume discount on them.

 

[COEngineeer]

Ok here it is. I guess I only need to retain 4-5 ft. I am retaining my side. I am retaining a walk way that is kinda curvy back and forward about 80 ft long. Thought about using MSE which i think the ideal situation but the contractor hasnt done any mse so I am little hesitant using it. Also, the city of vail doesnt allow us using exposed man made material retaining wall. Meaning the block of MSE wall has to be covered with additional 4" of natural stone veneer. So it is a lot easier to use concrete wall because I can just use a ledger, plus the face is much smoother to work with. So I think this is what i am going to do. I will have a wall about 5-6 ft high where it is only burried 1 ft on one side and retain 4-5 ft on other side. I will have a wall perpendicular to it every maybe 15 - 20 ft that will have helical pier at the end of it to act kinda like a counter fort. Then maybe put helical piers at every 10 ft under the retaining wall. What do you guys think?

 

[TDAA]

OK, for the relatively low height and the need for natural material, I would think of a stacked boulder wall. Not sure exactly where they are located, but I know there are several around town. We were asked to do some similar to pictures of some Vail walls shown to us.

MSE does not mean you have to do a block face; however, I would rather have an experienced contractor build that type of wall. Also, since MSE is considered to be flexible, you would have to be sure your stone facing could handle the movement.

I think your concept could work, although it seems overkill for 4-5 feet retained. Do you know the depth to, and type of, bedrock? This could impact the use of helicals.

 

[emmgjld]

A variation of MSE walls were done in Telluride Mtn. Village. Everything there is rock faced.

 

[COEngineeer]

Yes, this project is in Vail. I assume all mse blockings are man made material right? Because it has to be cut perfectly? Plus I think it is pretty big right? I dont think they have any natural stone block? That would be kinda pricy i think. That what I was thinking TDAA. It will be kinda hard to attach additional veneer. The number I gave you guys was only guesses. I will probably only put helical piers at both sides of counterfort. I will design the wall between each counterfort as Fixed Fixed hinged free. I have not done calc yet so I dont know how far apart the counterforts are going to be.

 

[TDAA]

By the way, how deep is the frost depth in Vail?, and how close are you to the adjacent that you could not excavate?

 

[COEngineeer]

4ft frost depth and the boundary line @ some places is as close as 3 ft.