When would a retaining wall footing be required?

[NC-ENG]

I have a wall that landed in the landscape plans (I suspect, but do not know for a fact that structural EoR would like to have taken a look at it but was never asked to by the LA). It is holding up a fire lane and 3-4' of retained earth at its tallest point. The wall is being called a "turn down slab", but I believe it should be a considered a retaining wall with a spread footing. The geotech report has 3,000 psf as the allowable soil bearing pressure. The fire lane would be considered used only in emergency conditions (not frequently loaded).

The wall itself is 10" wide 3,000 psi concrete. Reinforcing is #4 @ 12" oc vertical and #5 @ 12" oc. horizontal (turned back into the slab). I suppose the top of wall could be considered pinned or tied into the slab condition, although it is not poured monolithic with the slab and there is a CJ between the curb/top of wall condition and the structural slab.

The wall has settled around 2" over the last 2 years. It doesn't appear to be in danger of failure, but the design is being called into question on whether a foundation should have been provided.

What would the anticipated bearing pressure be at the stem of the 10" wall at the max retained earth section of 4' (3' plus 1' of cover). To make matters worse, the curb has scuppers at 8' o.c. which allows surface water to sheet down the wall, meaning the bearing condition is almost always wet/saturated.

 

[ANE91]

I work in jurisdictions that consider 4ft+ walls to be retaining walls and as such require footings. I also work in other jurisdictions that set the floor at 2ft. State building code should tell you.

I would consider this to be a retaining wall and would design it as such. Good eye on the saturated soil condition.

 

[Greenalleycat]

2" settlement in 2 years is crap work
Someone got it wrong

 

[NC-ENG]

I work in jurisdictions that consider 4ft+ walls to be retaining walls and as such require footings. I also work in other jurisdictions that set the floor at 2ft. State building code should tell you.

I would consider this to be a retaining wall and would design it as such. Good eye on the saturated soil condition.

I work in jurisdictions that consider 4ft+ walls to be retaining walls and as such require footings. I also work in other jurisdictions that set the floor at 2ft. State building code should tell you.

I would consider this to be a retaining wall and would design it as such. Good eye on the saturated soil condition.

Retaining walls less than five feet tall are not required to have a building permit. However, retaining wall systems less than five feet in cumulative vertical relief and adjacent to a structure located closer than the vertical relief shall be designed under the responsible charge of a registered design professional and shall require a building permit and inspection.

Just because it didn’t require a permit doesn’t mean it shouldn’t have had a footing. My question is whether or not the footing detail as shown would exceed the soil bearing capacity of 3000 psf

 

[NC-ENG]

2" settlement in 2 years is crap work
Someone got it wrong

The work met all required inspections and complied with the contract documents. Soil compaction and concrete testing were all monitored under special inspections. I agree that 2” settlement is a lot, but wouldn’t necessarily agree that it’s “crap work” when my contract doesn’t include any design obligations.

The question I have is does the wall as designed exceed allowable soil bearing capacity pressure?

 

[Greenalleycat]

Look, if this thing has settled 2" then someone has made a mistake - the performance in-situ makes that obvious, even if the paper process that was followed is the right one

 

[NC-ENG]

Look, if this thing has settled 2" then someone has made a mistake - the performance in-situ makes that obvious, even if the paper process that was followed is the right one

I’m not sure you understood the question…

The wall did not require a “permit” per se, but regardless it was part of a larger building permit on a large commercial project so that point is moot.

My question: how would one go about calculating the bearing capacity of the wall section provided? I believe it would need a footing, just from experience, but if the wall design stays under the 3000 psf allowable soil bearing capacity and within any factors of safety, the design engineer would be “off the hook” for repair costs.

The focus now is to attempt to determine where the fault lies so that the associated repair costs can be distributed.

 

[ANE91]

The question I have is does the wall as designed exceed allowable soil bearing capacity pressure?

Around these parts, you pay to have that question answered.

The wall did not require a “permit” per se, but regardless it was part of a larger building permit on a large commercial project so that point is moot.

I don’t believe that anyone here has used the word “permit” besides you.

The focus now is to attempt to determine where the fault lies so that the associated repair costs can be distributed.

Hire an attorney.

 

[Greenalleycat]

I’m not sure you understood the question…

The wall did not require a “permit” per se, but regardless it was part of a larger building permit on a large commercial project so that point is moot.

My question: how would one go about calculating the bearing capacity of the wall section provided? I believe it would need a footing, just from experience, but if the wall design stays under the 3000 psf allowable soil bearing capacity and within any factors of safety, the design engineer would be “off the hook” for repair costs.

The focus now is to attempt to determine where the fault lies so that the associated repair costs can be distributed.

Your tag says "structural" but your question implies you don't know much about structure - this is a basic design, you should be able to calculate it
I assume that you are actually not a structural engineer who is posting here under guise of getting free advice

Your OP says "It doesn't appear to be in danger of failure, but the design is being called into question on whether a foundation should have been provided."
You are misusing 'failed' in an engineering context
To me, this wall has already failed to meet relevant design criteria by virtue of settling 50mm in 2 years
It is therefore obvious that something different should be done, and if it has settled 50mm without a foundation, then it's a reasonable assumption that a foundation should have been provided - that is not rocket science

Your focus on whether a permit was required or inspections were done is irrelevant IMO
Someone took ownership of that design, either by engineering it or just deciding to build whatever took their fancy, and that persons design is wrong as evidenced by in situ performance
Now, it gets complex if an engineer designed it with bearing pressures provided by the geotech and the geotech got their numbers wrong
That is where the lawyers rub their hands in glee and you start contemplating whether it's worth arguing about right/wrong and just open your wallet instead

 

[StrucPatholgst]

If the slab and "wall" were poured monolithically, and the whole thing has settled 2 inches at the outer edge, then you should be more concerned with a slide or how the whole bank was worked/graded/compacted, not the width of any footing. To me it sounds like it's rolling out, like a row of shallow deck sonotubes on a hillside. Looks like the wall didn't stab far enough into the hill. Fails the old-salt-7-foot rule.

 

[NC-ENG]

Around these parts, you pay to have that question answered.

Working on it, but struggling due to potential conflicts of interest

I don’t believe that anyone here has used the word “permit” besides you.


Hire an attorney.

Just was in reference to “jurisdiction. The repair cost is ~$80k. Not small, but also not large enough to justify going legal route

 

[NC-ENG]

Your tag says "structural" but your question implies you don't know much about structure - this is a basic design, you should be able to calculate it
I assume that you are actually not a structural engineer who is posting here under guise of getting free advice

Your OP says "It doesn't appear to be in danger of failure, but the design is being called into question on whether a foundation should have been provided."
You are misusing 'failed' in an engineering context
To me, this wall has already failed to meet relevant design criteria by virtue of settling 50mm in 2 years
It is therefore obvious that something different should be done, and if it has settled 50mm without a foundation, then it's a reasonable assumption that a foundation should have been provided - that is not rocket science

Your focus on whether a permit was required or inspections were done is irrelevant IMO
Someone took ownership of that design, either by engineering it or just deciding to build whatever took their fancy, and that persons design is wrong as evidenced by in situ performance
Now, it gets complex if an engineer designed it with bearing pressures provided by the geotech and the geotech got their numbers wrong
That is where the lawyers rub their hands in glee and you start contemplating whether it's worth arguing about right/wrong and just open your wallet instead

I am an engineer, just don’t actively stamp/practice. Was construction engineering undergrad and took PE in civil, but haven’t ran calcs in 20 years. License is active, not that it matters in this situation.

I used the term failure in that it isn’t in danger of sliding down the hill. Nor is there obvious signs of settlement increasing. We shot grades over the course of a year and the settlement is actually slowing. This would check out with consolidation of clay soils or possibly a bearing failure or both. The wall does not appear to be in danger of sliding or overturning type failure.

Will not get to the level of legal. It’s simply not large enough of an issue. I doubt 3000 psf is wrong in the geotech. It is a common design soil bearing pressure with typical clayey soils in our area.

 

[NC-ENG]

If the slab and "wall" were poured monolithically, and the whole thing has settled 2 inches at the outer edge, then you should be more concerned with a slide or how the whole bank was worked/graded/compacted, not the width of any footing. To me it sounds like it's rolling out, like a row of shallow deck sonotubes on a hillside. Looks like the wall didn't stab far enough into the hill. Fails the old-salt-7-foot rule.

Wall was poured first. Slab was poured on top.

Rolling out seems to be the most likely source. There is a section of slab behind in the photo that shows the amount of roll. It isn’t noticeable roll. Just a slightly larger joint than normal and instead of 1/4” per foot slope, it’s probably closer to 3/8”/ft. Not really an aesthetic issue other than the joint being ~1”. It also doesn’t stand out against the building since the joint from sidewalk to building is ~3/4”

 

[TRAK.Structural]

As others have said, the joint in the slab close to the "wall" is likely too close to hold it all together.

Regardless, I would have put a small footing under the wall. I've seen similar details to this used inside of a building where the floor elevation changes, but there is always a slab on the low side that helps to prevent any kind of lateral movement at the base of the "wall".

calculation of the bearing pressure under the "wall" is a simple load/area exercise; however the condition of the soil under the slab near where the transition occurs is key for this calculation to be accurate. Consolidation or loss of material under the slab may be sending extra load to the "wall".

 

[NC-ENG]

Thanks for the response.

I suspect that there is some pinning and agree that consolidation under the slab is probably adding to the load on the wall. Certainly not ideal to have all of that focused on a 10” wall on top of soil continuously exposed to water from the scuppers.