Parking Area Retaining Wall

[XR250]

I have a retaining wall on two sides of a residential parking area. Due to property line issues, the heel of my footing is very small. As such I have a sliding problem. I tried a keyway but it was not very effective. How do y'all feel about me using the parking slab for the additional sliding resistance? Ok to use expansion joint material and just let it slide a tiny bit? This is the architect's drawing, not mine.

 

[XR250]

Thanks for all the responses. As I said in my last post, 2 ft. does work so I will likely use that. It is a rocky site so it may be a challenge to even get that 2 ft.
@Bones - I suggested an MSE wall, but that is not the look they want.
@Aesur - point taken. Maybe a discussion we should bring over to the "IRC Prescriptive Limits" thread as theoretically, basement slabs are used to brace the bottom of basement foundation walls.

 

[XR250]

This is more money, but what if you drop the footing another 1.5 to 2ft? Then, you can pick up some more passive pressure?

It is close to the property line so they are worried about slope stability during construction. The deeper the footing, the steeper the excavation.

 

[DoubleStud]

@Aesur - point taken. Maybe a discussion we should bring over to the "IRC Prescriptive Limits" thread as theoretically, basement slabs are used to brace the bottom of basement foundation walls.

True, but most houses the walls jogs. The walls perpendicular to it will help. The walls across the slab will help with the sliding as well. Interior framed wall will help as well.

 

[phamENG]

And most basements have an opposite wall to push back on. Will this one?

 

[GeorgeTheCivilEngineer]

It is close to the property line so they are worried about slope stability during construction. The deeper the footing, the steeper the excavation.

Just out of interest - how are they going to build it if it is that tight?

 

[XR250]

Just out of interest - how are they going to build it if it is that tight?

That's a means and methods issue. Maybe they can get the adjacent property owner to play ball.

And most basements have an opposite wall to push back on. Will this one?

Fair point. Honestly, though I have never even seen the gap around a slab expansion joint close up in a basement so I imagine the footing is doing all the work.
Think in reality the friction and passive pressure numbers we use are probably low

 

[DoubleStud]

I think most basements act like a concrete tank and the horizontal rebars do heavy lifting even though the walls are designed to span vertically.

 

[XR250]

Most older basements I run into are un-reinforced masonry but I do think some 2 -way action is helping.

 

[bones206]

@Bones - I suggested an MSE wall, but that is not the look they want

I thought MSE walls are available in a wide variety of finishes and block options. It does seem like the best option given the constraints.

 

[XR250]

They want a smooth stucco finish. Not sure that is possible with MSE walls.

 

[bones206]

We don’t do much stucco here in Maine, but I would think it would actually be a little easier with a rough face block versus a smooth face CMU. But maybe not.

 

[gte447f]

bones206, per the OP, I think the property line is on the heel side of the wall. That means MSE wall would not be an option because geogrid would have to be on neighboring property.

XR250, correct me if I am wrong.

 

[gte447f]

I would expect stucco applied to an MSE wall to crack to all hell. The walls are very flexible and stucco is very brittle.

 

[bones206]

Ah, that makes sense.

 

[XR250]

XR250, correct me if I am wrong.

That is correct but still maybe enough room to get the geogrid in if you are ok with almost a vertical excavation.

 

[Aesur]

It is a rocky site so it may be a challenge to even get that 2 ft.

Out of curiosity, if there is a geotech report, can you rock dowel the foundation to bedrock if close enough to resist sliding? I have had a few sites where we were able to do this.

It looks like others touched on why basement walls I agree with using the slab to resist sliding; I have nothing further to add beyond what others have added for the use of basement slabs.

 

[Brad805]

MSE is basically a wall tied with Geogrid. If the courses are the same, you can tie the two walls together by laying a grid over. Given your heights, the forces do not seem large. I could be misunderstanding the problem however.

 

[gte447f]

Brad805, are you talking about tying the retaining wall and the planter walls together? The issue in the OP is global sliding of the combined walls since they share a footing (retaining wall and planter wall). I don't think your suggestion of tying the 2 walls together is relevant.

 

[Aesur]

MSE is basically a wall tied with Geogrid.

Aren't you required to do a more in depth global stability analysis for MSE walls?

 

[Brad805]

Aseur, I meant in general terms. We get a geotech or supplier engineer to design the grid.

gte, yes, the idea I had is sketched below.