Seatwall design

[broekie]

I have been asked by the site civil engineer on a project that our office is working on to design something called a seatwall. Basically what it is (from existing details) is a 16" wide retaining wall that extends 3'-6" below grade on the low side of the wall. The difference in grades that I have on this wall is approximately 2'-6" from the low side to the high side. In other words, my wall is 6'-0' high with 2'-6" of the wall visible.

The civil engineer wants to construct another one of these walls on the site and has asked me to look at the design. The existing wall does not have a footing, but I am not sure how the original designer justified that the wall works. When I look at overturning of the wall like I would a retaining wall, the overturning moment is larger than the resisting moment. I want to put a footing on the wall, but according to the civil engineer the owner doesn't have enough money for this. I am wondering if there is another way to look at this, like a sheet pile wall or something. I am not going to compromise what I think the right thing is to do, but I am curious if any of you have run into a case like this or have any suggestions. Any help would be appreciated. Thank you.

 

[JAE]

I would think its behavior is just like that of a sheet pile wall. When you look at overturning, the mistake is that one assumes the rotation point at the bottom of the wall (like it is for a traditional cantilever retaining wall). For sheet pile walls, the rotation point is some distance up the wall from the bottom.

You can use sheet pile wall design techniques on this.

 

[broekie]

Thanks, JAE.

I ran some numbers using sheet pile wall calculations and got a embed depth of 3.3', which matches up well with the existing plans showing 3'-6". That must be the design technique the original designer used.

 

[UcfSE]

Have you gone to the existing site to observe the wall and see how well it has performed? That might help clue you in to how well the design as worked so far.

When you look at the sheet pile equations, check to see if they assume a flexible or rigid wall. That will affect your calculations some what, though for a short wall like this it may only be an academic point.

 

[broekie]

We have visited the site, and the wall is performing just fine.