Strengthen existing retaining wall

[broekie]

I am working on a project where the client has an existing retaining wall that needs to be raised a couple of feet. The wall is holding back an earthen dam. The problem is that when I analyzed the existing wall with 2 additional feet of height, the bending moment capacity at the base of the wall is not enough. I need to strengthen the wall.

I was thinking a couple of deadmen attached to the wall, but we don't want to dig out the earthen dam (and risk compromising its integrity) to install the deadmen. What about helical anchors? Does that sound like a good possibility? Is there anything else out there that could be used? I don't have a lot of experience in this area. Thanks.

 

[msquared48]

In another string in this forum, I remember someone recently mentioned about using helical anchors to stabilize the sidewall of a dam spillway that had moved. Could be the answer to your problem.

Mike McCann
MMC Engineering

 

[cvg]

anchors penetrating into the dam embankment probably will not be allowed. how about building a second wall along the front side?

 

[Mickney]

Amazing how 2-feet of soil can have this much impact, however, I am not aware of how large the embankment dam is.

This may sound crazy and I am not a big proponent of drilling soil test borings through an embankment dam, but consult with your geotechnical engineer for the project. More specifically, talk about the soil parameters (unit weight, friction angle, etc.) used to calculate the lateral earth pressures. Were these based on actual laboratory data or were conservative assumptions made based on soil types. Even so, drill a few borings, collect some undisturbed samples, run some laboratory testing and utilize in-situ conditions. If conservatism was built into the design, see just how much conservatism was used. It may be that you have very different earth pressures and soil strengths than what the wall was originally designed for.

Keep in mind that the balance may teeter in the opposite direction than desired in that the wall was underdesigned for the soil types. Also, grout the borings if you drill through the embankment.

 

[fattdad]

If the wall can accomodate the horizontal stresses and you are just dealing with bending moment, you may be able to install vertical post-tensioning elements. Not sure of your details, but if you can retrofit the wall to increase the compression, you may be able to mitigate the bending stresses.

Just a thought . . .

f-d

¡papá gordo ain’t no madre flaca!

 

[civilperson]

Counterforts or buttresses could help on moment resistance, changing a cantilever wall to a wall fixed at two sides and bottom. Roark gives coefficients of moment at bottom of wall at 45% of the cantilever moment for triangular load.

 

[cvg]

counterforts is a good idea and commonly used on dam spillway walls.