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Cutting Small deck footings into geogrid/retaining wall

Cutting Small deck footings into geogrid/retaining wall

(OP)
Its a segmental wall ranging from 4' to 6'. There are a couple layers of geogrid in it. Contractor wants to put a couple of 6x6 deck posts with probably a 12x12 concrete footing in the reinforced zone. Any tips on how to accomplish this? First thought was to go down to the base height of the wall so the additional surcharge load is not on the wall. Other option is to set it at the top and try and bound the design with the surcharge load. It won't be very big, few kips.

I've seen the allan block details for fences, etc. I also have the NCMA SRW design software for use. Thoughts?

Thanks

RE: Cutting Small deck footings into geogrid/retaining wall

I would not dig though the reinforced zone. Instead, if frost depth is not a problem, use shallow footings but size them larger than 12 x 12, and/or use more than the minimum (a couple?) number of posts/footings. Distribute the load, but leave the wall and it's backfill alone.

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RE: Cutting Small deck footings into geogrid/retaining wall

How far down is the first layer of Geogrid. It may below frost and not an issue to be cut by the footing.

Additionally, even though it is a code issue, so what if there is a little frost heave with a "small" deck?

Mike McCann, PE, SE (WA)


RE: Cutting Small deck footings into geogrid/retaining wall

(OP)
So I spoke with the contractor and apparently they have already cut through the geogrid all the way to the bottom of the wall and sounds like the county won't pass it without a stamp on it. Going to look at it on Friday. Always nice when they pull the engineer in on the back end.

Frost depth is not a problem 12" below grade is all that's required.

RE: Cutting Small deck footings into geogrid/retaining wall

How old is the MSE wall? Maybe you can call the designer and have him check his wall for isolated grid damage at each post location. You may need to pay him but it might not be excessive.

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RE: Cutting Small deck footings into geogrid/retaining wall

So haw big is the cut in the mesh, and how far back from the face of the wall?

Why the H(&) did he go through both layers of mesh? Did the bottom need to be founded in China?

Mike McCann, PE, SE (WA)


RE: Cutting Small deck footings into geogrid/retaining wall

(OP)
Not sure how big the cut is. Hopefully its just a 12x12 and nothing bigger. I'm gonna guess its right at the wall. Maybe a foot or so back. I'll take some measurements on Friday.

I believe its a fairly new wall but since its 4 ft (our code doesn't require an engineered wall 4ft and less) to 6 ft in some locations and its residential, I doubt an engineer sealed it or even looked at the original wall.

Not sure exactly. It appears they were trying to lead me down that path since it turns out they already did it. Its 3 layers on the 6 ft wall.

RE: Cutting Small deck footings into geogrid/retaining wall

(OP)
It just keeps getting better. Because they dug so deep what was a small hole turned into a 3'x3' hole....

I think they are just going to have to dig out wider in the hole locations at each column and lap the mesh per standard type details. Basically rebuild the wall in those locations. Don't really see any way around that.

RE: Cutting Small deck footings into geogrid/retaining wall

Sounds like you are dealing with a holey contractor.

Mike McCann, PE, SE (WA)


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