Cantilevered retaining walls top deflection 1

[bierot]

I'm working in the design of some quite high cantilevered retaining walls (height of the stem around 9.50 meters), and I'm worried about the horizontal deflection of its top due to the stem deformation (elastic and due to long term loads). Since the earth pressure varies with the deformation of the stem from the "at rest" coefficient to the fully active one, I guess the correct way of calculating this deflection must be difficult. Since it is a common problem I guess there must be easy formulas available to estimate it. Does someone know where I can find some formulas or charts to calculate this deflection?

Thank you very much,

Xavier Font
MLM Consulting Engineers
Ipswich, UK

 

[haynewp]

Did you consider something other than a cantilevered wall?
Counterfort wall or maybe a reinforced earth system?

 

[PEinc]

If the wall is a fill wall, try MSE or RECO walls. If the wall is in a cut situation, try a permanent tiedback wall.

 

[broekie]

If you do use a cantilevered wall, batter the front face of the wall back toward the soil. That way when it does deflect, the front face of the wall will appear vertical.

If the front face of the wall is vertical, when it deflects, it tends to make the public a little nervous with a wall of that height.

 

[bierot]

I started to work in this project in a late stage. The planning drawings are already approved by the Railway Network Authority with this design and now I’d be hard to change it, so I should do my best with this typology. My idea is to design the toe and the heel of the base to get an almost uniform distribution of bearing stresses under permanent loads (doing in this way I will limit the rotation of the base and so the lateral displacement of the top of the stem). For the deflection due to the deformation of the stem, I’m thinking in increasing the thickness of the stem up to an appropriate value (I’d like to avoid the use of anchors). For this reason, in order to choose this thickness, I’m trying to find an easy way of estimating this deflection. The problem is not only an aesthetical one (I’m also thinking in battering the face of the wall) but some of these walls are next to the abutments of a bridge whose deflection will be lesser because the deck is used as a strut.

Thanks again,

Xavier Font
MLM Consulting Engineers
Ipswich, UK

 

[PEinc]

You could also try a counterfort retaining wall. This will stiffen the stem.

If the wall is in a cut situation, you still may need temporary sheeting and tieback anchors. In effect, you will be building two walls, one temporary and one permanent. In situations like this, a permanent tiedback wall becomes economical. But you would need a permanent easement for the tiebacks.

 

[DRC1]

I assume this is a fill wall. If you use plate tampers or small rollers with about 5-7 feet of the wall (avoid large equipment in this area) you will probably have a distribution that approach Ko conditions. You need considerable deflection and rotaion to get Ka conditions, which give you lighter loads. I would just estimate wall deflection as a triagular Ko distibution, adding in the effects of any significant surcharges. The truth of the matter is that wall deflections are not very precise, but rather a rough estimate.