Inverted "L" cantilever retaining wall with tension anchor

[thomas623]

I am designing an inverted L cantilever retaining wall.

The retaining height is 14m but the design ground water is at 10m high. Therefore, high uplift pressure is acting the footing base and tension anchors are required to maintain the FOS against uplift.

However, when i evaluating the FOS against sliding, i am stuck.

FOS|SL = V tan phi / H

But what should be V (total downward load) in this case? How to manipulate the contribution due to the tension anchor? I can find any publication mention about it.

 

[six06]

so by inverted you are saying that the fill wont be in contact with the foundation of the wall?

 

[cvg]

this sounds suspiciously like a floodwall. check out the USACE engineering manual for floodwall design.

em 1110-2-2502 Retaining and Flood Walls

http://140.194.76.129/publications/eng-manuals/em1110-2-2502/toc.htm

 

[moe333]

I'm assuming you have groundwater 4m above the foundation of the wall and that you will need to dewater to construct the wall. I think there are some other issues but to answer your question:

You would want an effective stress so I would think V would equal the allowable anchor load minus the 4m of head from the groundwater. You may want to consider a higher head for design.

 

[thomas623]

A preliminary section is attached.

It is a part of a building which need to be retained

 

[RFreund]

I don't mean to distract from your question, but I'm curious as to how you found the uplift pressure distribution.

 

[apsix]

There is nothing obvious inverted about that L.

 

[csd72]

Is there another similar wall on the other side? Can you then use the floor slab to resist the sliding?

If not have you considered using raked tension anchors?

 

[msquared48]

You have a very inefficient L shaped wall here with no heel soil load to resist overturning or sliding.

You will need a concrete keyway to resist the sliding, and the tension rods you mention to resist overturning. You are also very likely to need a high soil bearing allowable at the tip of the toe for this to work at all.

At 14 meters high, is there no hope for tiebacks, or is the other building too close?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[thomas623]

there are so many constraints in the design.

it's already the site boundary behind the wall so that we cannot have the normal L shape retaining wall.

The building will be built "embed" in a slope hill. Two of adjancent sides will have to design for retaining the soil.

The rockhead is very high, only about 3m below existing slope profile. therefore the groundwater level is high too due to impermeability of rock.

therefore, huge uplift pressure present due to the pressure head different under the footing.

 

[Geostructsparks]

It sounds like you should plan on adequate drainage to lower the water level to at least the bedrock surface, and have drain rock all the way down. If you don't do an open excavation with room for back formwork near the rock, which would allow for a big gravel drain, how do you propose to build this wall against the bedrock?

If those are conventional drilled shafts on both sides, I believe there are conventional methods to treat it as a pile cap. Seems costly though. Since you are in bedrock, I don't see settlement causing tension to be reduced being a problem. I would think you could perhaps put in less anchors (a line near the wall face which would also reduce overturning and bearing at the toe) At that point the foundation design is similar to a simple concrete beam, and you could probably determine bearing pressure for a known selected anchor force.

 

[molerat2210]

Why not a keyway?