What's up with retaining wall footings and details

[theory2code2practice]

I've seen a bunch of premade block walls with their standard footing only being about 16" to 18" below grade. I've also seen some older books with standard retaining wall designs showing footings for concrete or masonry retaining walls also only about that depth. Is there any consideration for frost depth when it comes to these designs? is there any code reference specifically talking about footings for retaining walls?

Along the same line of questioning, I've seen many different variation in for size, location, spacing and backing for wheepholes. Any code reference for that? Same goes with gravel fill behind the walls for drainage. Any reference?

I've been designing for quite a while, and I'm wondering what other's practice is. A lot of details that are common place seem to be taken for granted and I was wondering if there was a source for any of it or if its a "if it aint broke dont fix it" kinda thing.


Thanks in advance.

 

[JAE]

We try to set the footings below frost and this goes along with us trying to create enough passive pressure to avoid sliding.
Both tend to go hand in hand.

 

[michaelmiles]

We try to set the footings below frost and this goes along with us trying to create enough passive pressure to avoid sliding.
Both tend to go hand in hand.

Absolutely, you're right. Placing the footings below the frost line is crucial to avoid damage from freeze-thaw cycles, and at the same time, it helps in mobilizing sufficient passive earth pressure to resist sliding. These two considerations often align naturally in design

 

[JAE]

I might add that "premade block walls" might be referring to mechanically stabilized block wall (MSE) systems where the base is usually just a packed gravel trough and not below frost. I think the reasoning is that the sliding isn't an issue (the geogrid resists overturning and sliding) and up-down flexing of the wall along its length due to freeze/thaw movement can apparently be tolerated by the MSE system.

 

[JStephen]

Those designs may just come from the significant parts of the US that don't have frost issues.