Geotextile Reinforced Retaining Wall

[bookowski]

Being lazy here, I have not looked into this much yet but it's a construction issue so in the interest of time I am hoping someone with experience in the design of these walls can give a gut level opinion here before I dive in.

I've got a small new building (1 story steel frame) adjacent to an existing keystone retaining wall. The wall is 11' tall from t.o. wall to grade. Our proposed footing is down 5' from grade, so 7' above the b.o. wall and is offset 10' from the b.o. retaining wall (that's to the edge of our footing). So I've got a line at 10H:7V from b.o. wall to b.o. footing. We have the original wall design drawings (it's relatively new) and the fabric is specified just under 10ft, so just outboard of our proposed footing. These details were missed during the initial design and if I had caught this I would have pushed the footing deeper, but now i'm stuck doing it during excavation and trying to minimize how much yelling I have to endure. The contractor/owner side are pushing that it's fine but I did not agree.

I was able to contact the original designer. He worked for the wall company and is now retired but we've had a few back/forth emails. His suggestion was to push the footing down all the way to the adjacent grade, i.e. b.o. footing 11ft down. This seems excessive but I am not familar with the design of these walls. From our emails I am getting the impression that his design is likely prescriptive or based on some rules of thumb (i.e. "fabric went back 10ft because it's about a 10ft tall wall"). Now that I've got him in the loop I don't want to ignore his suggestion.

My 2nd concern is that if they do dig down to the full depth, 11ft, right off the face of the fabric this seems likely to disturb the reinforced soil. Short of driving piles or some other support of excavation I don't see how that won't become a mess. The could pile support that side of the building but I'm hoping to avoid that.

 

[LOTE]

This would be pretty easy to model the wall with the vertical load from the footing applied to the wall. I would have the wall designer model it. Worst case is the wall will need stronger grids or more grids below the footing (assuming the wall is not build yet or the wall gets rebuilt). You should also check global stability (with FS>1.5 since the wall is supporting the building).

Something to keep in mind, with all SRW/MSE walls, the wall structure is the entire limits of the facing and geogrid, not just the block facing. You should treat the back of the geogrid reinforced zone as the back of the wall.

Is the Keystone wall already built? You will definitely disturb the wall if it is. Even driving sheeting, you risk hitting the tails of the geogrid and pulling down the grid as you drive the sheeting. I would consider rebuilding this section of the Keystone wall. The contractor could reuse the blocks and replace the geogrid.

 

[gte447f]

LOTE, wall is already existing.

 

[gte447f]

bookowski, this is messy and certainly not ideal to be dealing with this after design/during construction. Unfortunately, I agree with LOTE that both the final completed construction of your building and especially the construction process are likely to affect the existing SRW wall.

 

[bookowski]

Wall is existing, original designer is retired and willing to shoot some emails but nothing beyond that. It's about 100 linear feet of new proposed strip footing adjacent to the wall. Piles sound easier than taking down the wall and rebuilding it.

 

[LOTE]

bookowski - do you know if a global stability analysis was performed considering the building?

 

[bookowski]

Sounds like piles will be the least painful solution.

Lote - The original wall designer via email said that the walls are all designed for 100psf live and dead surcharge at the surface. I don't expect to get much more out of him, he is retired.

 

[BridgeSmith]

I mostly looked at this thread because of the title. Geotextile? You do mean geogrid, right? So, you're considering a mechanically stabilized earth (MSE) retaining wall? Geotextile is a whole different animal, and poor reinforcement for an MSE wall.

 

[bookowski]

Correct, it should have said geogrid.