Retaining Walls: Drainage

[Esteban6112]

Hi,

Does a retaining wall with a toe but no heel, need a drainage system?
At first glance, I thought the drainage would work for water accumulated above the heel of the retaining wall, but without a heel the water would not accumulate.
Can someone explain if I need the drainage with no heel.

Thank you,

Esteban

 

[JoelTXCive]

Heel or no heel; I think you need drainage unless site conditions are such that the water table will never rise up above the bearing depth of the footing.

If there is any chance that the water table can come up, then you need a way to relieve pressure; or design the wall for a fully saturated un-drained condition.

 

[Ron247]

A retaining wall with no heel is not a cantilevered retaining wall, it is a strip footing. You need to really consider what your are simulating.

 

[Settingsun]

They're still called cantilever retaining walls where I'm from and drainage will be important. Try getting the numbers to stack up for saturated backfill vs dry. Unless you have the base slab at a decent depth below ground so have decent stabilising dead weight despite not having a heel.

 

[Ron247]

Without a heel, the water can still accumulate. Where I work, no heel is not a retaining wall, it is a strip footing. Drainage on a retaining wall drastically changes your lateral loads. No drainage, much higher lateral loads.

 

[hokie66]

Ron,

For a wall to be a retaining wall, it just has to have soil higher on one side than the other. And to be a cantilevered wall, it is not supported at the top. But then there are propped cantilever walls...

Drainage is good practice behind retaining walls, but consideration should be given to blockage of the drains, which is common.

 

[bridgebuster]

Let's not get testy over terminology. In my area we call it an L-shaped wall.

 

[r13]

If possible, weep holes will help, when drain is clogged.

 

[HouseBoy]

"A retaining wall with no heel is not a cantilevered retaining wall, it is a strip footing."

Maybe I'm misunderstanding this but... we refer to this as a "Property Line Retaining Wall".

Assuming the adjacent property is the "high side" I can guess why there might be a question about the drainage (since the whole purpose is to build it right on the property line). If a footing can't be placed there, then gravel for drainage might also be difficult to install.

Naturally there are other issues with excavation and overdid but to answer the question:
Either there needs to be drainage OR the wall must be designed for the wet soil characteristics that will be there.

Property line retaining wall footings are not very efficient (general rule is that the footing is as wide as the wall is tall).
Sometimes when working on a property line, we utilize drilled piers and lagging.

 

[r13]

HouseBoy raises a very interesting situation. As a property wall, you would need to put more thoughts into the design, as anything wrong with the next door, it will be automatically pointing to you, no matter the fact. Maybe use method as suggested by HouseBoy, or maybe back the wall a few feet to provide space for quality back fill. I know the owner wouldn't like this idea, but without try, who knows.

 

[bridgebuster]

@Esteban6112 how come you can't build a heel? I'm trying to picture this; are you up against someone's property as HouseBoy asked? Could you post a sketch? I've inspected 100's of walls and a wall without drainage is asking for trouble.

 

[mchen96]

Need? It doesn´t need one. But you probably want it:

If I had a situation in which drains were unacceptable, I'd make sure that the wall could take the hydrostatic pressure of water accumulating behind the wall(which would result in a much thicker and more expensive wall).

The lack of a heel will not necessarily stop water from accumulating. Unless the soil is so porous that there is no conceivable way for the water table to rise (maybe you're building on top of gravel or something), I would either add drains or design for the hydrostatic pressure in addition to the effective lateral earth pressure.

 

[Esteban6112]

@bridgebuster yes, the reason I asked is exactly because of what @HouseBoy mentioned.

 

[Tomfh]

Water can still build up behind the wall.

You should put drainage behind the wall, even it is just gravel which can drain out at the ends.