Retaining wall as One Way Horizontal Slab

[AlpineEngineer]

I have a tall basement retaining wall (18ft) that I wish to design as a horizontal one way slab system (not a typical vertical one way slab/beam)because my horizontal dimension is much less than my vertical dimension. I have perpindicular walls at the ends of the subject wall that can restrain the horizontal one way slab. I assume I can design the wall as 12" wide horizontal strips and in accordance with ACI 318 one way slab provisions. I'll verify I have enough mass/friction on the perpindicular walls to resist the end reaction and develop the horizontal steel into the perpindicular walls.

My questions are: Do you see any problems with this? Do I really even need to worry about much of a footing on this wall (other than self weight of course)? Do I have shear concerns at the ends of my wall? Reading ACI I don't get the impression I have to worry about shear at the ends for this case. I plan to install #4 vertical at 12" o.c. for temp, shrink, and force distribution.

 

[JAE]

"If the foundation is well drained, there should be no water table above the basement floor".

Not sure that is always true BAretired. You can have a naturally high water table condition (such as that found in Grand Forks, North Dakota - 2 feet deep always). A foundation drain won't do you any good in that condition unless it is pumped out - and only then it works if the pump can draw down the water table - depending on soil porosity, etc.

 

[BAretired]

It is not always true, JAE. In such cases, the design requires special attention but this was not mentioned in the original post.

BA

 

[hokie66]

I never depend on foundation drains to reduce pressure. Good to have, but they eventually stop working.

 

[msquared48]

JAE:

Correct, 50 psf/ft. Glad you clarified that.

Hokie:

And bottles run dry too (as in fail), right?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[BAretired]

Our code recognizes the benefit of a drained foundation in controlling water pressure and so do I. Otherwise, it would be necessary to assume a high water table in every foundation, something which is not common practice in my neck of the woods and evidently not in Mike's neck of the woods either.

BA

 

[AlpineEngineer]

Thanks for the great discussion. Apparently I confused active and at rest with at rest being more stringent. Now my question is: when do you use either of these? I thought for a typical cantilevered retaining wall you use active, is that right?
What is typical for a normal basement wall restrained at the top and bottom? I can't remember what ASCE says. I thought for basement walls ASCE allowed you to use active? Thanks.

 

[hokie66]

For typical cantilevered walls, use active pressure. At rest soil pressure should be used for basement walls. I don't know or care what ASCE says.

 

[BAretired]

At rest pressure is the horizontal pressure which occurs naturally in soil at depth. It is the pressure which occurs with no lateral movement at all.

Active pressure is used for cantilever retaining walls, but it requires a certain amount of movement in the wall to justify it. If the wall is very stiff, the pressure will be greater than active, but if the wall can't take it, it will simply yield until active pressure is achieved.

Passive pressure occurs when you push a wall or a foundation against the soil so as to fail the soil. It requires lateral movement into the soil mass.

BA

 

[a2mfk]

Well put BA, this is the way I have always been taught, read in Geotech books, and designed walls...