ACI supersede IBC - Gravel Footings
ACI supersede IBC - Gravel Footings
(OP)
I put both elements of this question in the title hoping to get feedback from those that might have familiarity with either topic.
A subcontractor on a project is proposing the use of gravel foundations for a 4 story wood framed building we are doing. These gravel foundations are intended to work in conjunction with precast concrete foundation walls which are used on residential buildings governed by the IRC (3 stories or less). Because these buildings are 4 stories, they fall under the IBC which doesn't make mention of gravel foundations and after a call to ICC committee are not approved for use in IBC governed buildings.
The subcontractor has proposed that since their foundation walls are an "engineered system" as defined by the ACI code which therefore supersedes the IBC and should therefore be permitted.
I have two concerns:
1. I have no experience with a system, any system, that claims precedence over the IBC unless very explicitly done (and I don't know of any that do)
2. I don't have confidence in gravel foundations under a 4 story building for several reasons such as: differential settlement possibilities between the wall footings and interior column footings, in plane shear loads, and wall chord forces.
Does anyone know of this reference about the building code?
Has anyone designed a 4 story or larger foundation on gravel footings?
A subcontractor on a project is proposing the use of gravel foundations for a 4 story wood framed building we are doing. These gravel foundations are intended to work in conjunction with precast concrete foundation walls which are used on residential buildings governed by the IRC (3 stories or less). Because these buildings are 4 stories, they fall under the IBC which doesn't make mention of gravel foundations and after a call to ICC committee are not approved for use in IBC governed buildings.
The subcontractor has proposed that since their foundation walls are an "engineered system" as defined by the ACI code which therefore supersedes the IBC and should therefore be permitted.
I have two concerns:
1. I have no experience with a system, any system, that claims precedence over the IBC unless very explicitly done (and I don't know of any that do)
2. I don't have confidence in gravel foundations under a 4 story building for several reasons such as: differential settlement possibilities between the wall footings and interior column footings, in plane shear loads, and wall chord forces.
Does anyone know of this reference about the building code?
Has anyone designed a 4 story or larger foundation on gravel footings?
PE, SE
Eastern United States
"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi






RE: ACI supersede IBC - Gravel Footings
However, it's unclear what you mean by "not approved". Do you mean that per the ICC committee, gravel foundations aren't allowed? Or that they just haven't specifically approved them? If it's the first, they are out, no question. But if it's the second, the subcontractor may be correct.
Brian C Potter, PE
Simple Supports - The history and practice of structural engineering.
ConstructionPic - Send annotated jobsite photos.
RE: ACI supersede IBC - Gravel Footings
PE, SE
Eastern United States
"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi
RE: ACI supersede IBC - Gravel Footings
If there is a choice between two systems, the one with the more stringent requirements prevails. See Chapter 1 of the IBC under alternate materials and methods.
RE: ACI supersede IBC - Gravel Footings
RE: ACI supersede IBC - Gravel Footings
A gravel foundation does not do the following:
It provides no uplift resistance so if your building is subject to wind loads, you can't meet the requirement for a continuous tensile tie from the foundation to the roof. Separate anchorage would be required.
If you are in a seismic zone of any import, you have no tangible mass in the foundation that can assist the structure in any way.
If you are in an area of soils that could migrate into the gravel (and almost any soil will...some worse than others), you have a settlement potential that is not clearly predictable.
If you are in an area of high rainfall or flood potential, you have a tremendous undermining potential that could place the structure at jeopardy for stability.
Personally, I would not allow this. Further, it is not an "approved" system and therefore does not meet the requirements of Section 104 of the IBC.
RE: ACI supersede IBC - Gravel Footings
Mike McCann
MMC Engineering
RE: ACI supersede IBC - Gravel Footings
The geotech was not aware they wanted gravel foundations at the start of the project so did not make that part of his report. We have stipulated since the start of this discussion that they be brought back on board to approve before we consent.
No, these are not geo piers. Those would be a different situation. These are literally trenching a strip, as you would for a wall footing of concrete, and filling it in with gravel then compacting.
Ron, great list. Many are concerns we have had but it's great getting another engineers consensus on the same issues.
PE, SE
Eastern United States
"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi
RE: ACI supersede IBC - Gravel Footings
Like Ron, I would never do that here from what I can imagine.
Mike McCann
MMC Engineering
RE: ACI supersede IBC - Gravel Footings
We are skeptical to say the least but are being squeezed from both sides to approve this.
PE, SE
Eastern United States
"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi
RE: ACI supersede IBC - Gravel Footings
But I'm being (or trying to be) silly.
Ron's list is perfect.
RE: ACI supersede IBC - Gravel Footings
Eric McDonald, PE
McDonald Structural Engineering, PLLC
RE: ACI supersede IBC - Gravel Footings
Mike McCann
MMC Engineering
RE: ACI supersede IBC - Gravel Footings
RE: ACI supersede IBC - Gravel Footings
RE: ACI supersede IBC - Gravel Footings
That may be OK for bearing, assuming it is not eventually undermined, but any uplift resistance needed to resist wind or seismic forces will just not be there as Ron stated unless concrete deadmen are also provided. I guess these would blow the contractor's budget... WOW!
This is very plainly just a very bad idea.
Mike McCann
MMC Engineering
RE: ACI supersede IBC - Gravel Footings
RE: ACI supersede IBC - Gravel Footings
RE: ACI supersede IBC - Gravel Footings
RE: ACI supersede IBC - Gravel Footings
Mike McCann
MMC Engineering
RE: ACI supersede IBC - Gravel Footings
RE: ACI supersede IBC - Gravel Footings
RE: ACI supersede IBC - Gravel Footings
I thought the op said the building had precast concrete foundation walls. He never said how thick or how deep these walls were. I still think this is the geotech's call.
RE: ACI supersede IBC - Gravel Footings
RE: ACI supersede IBC - Gravel Footings
I see, on rereading. In that case, they would be precast concrete footings. Gravel foundations perhaps, but not gravel footings, in my lingo at least. Acceptance of any system is not something I leave wholly to a geotechnical engineer.
RE: ACI supersede IBC - Gravel Footings
I think the idea of the gravel footings came from the Permanent Wood Foundation concept, years ago. At least, that’s the first time I saw it, and they do call them gravel or crushed rock footings. It was meant as a footing immediately under a 2x10 or 2x12 PT sill plate. You dug a 16 or 18" wide trench, 12 or 14" deep, filled it with compacted crushed rock and set the found. wall sill plate right on top of the crushed rock. It was also intended as part of the perimeter and under floor drainage system, and was tied into the exterior perimeter drain tile system. I always thought that they might as likely collect (attract and hold) water, and eventually fill with fines and be ineffective. They weren’t using any geotextile fabric wrapping in the early years. They could be built in winter without worrying about cold weather conc. practices. And, they performed best on sites with soils which drain well, sand or other granular soils. Some crazy contractors or builders expanded that concept to digging a trench filling it with a couple feet of rock and pouring an unformed stem wall on the rock for houses, etc. I’ve never seen it used for four stories, the most was two above grade floors and a basement wall which used the PT wood found. details. I’ve been involved in 6 or 8 cases over the years on this building technique, and those turned out poorly because the builder had no idea what he was really doing and used bad details, improper materials and poor waterproofing methods. Of course differential settlement could be a problem, for lack of the stiffness a poured conc. wall or a conc. blk. wall would offer.
RE: ACI supersede IBC - Gravel Footings
http://www.superiorwalls.com/downloads/reports_fil...
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MAP
RE: ACI supersede IBC - Gravel Footings
I would not go 4 stories. The foundation is the last place you want to try to save money as it is the hardest and most expensive to fix later.
RE: ACI supersede IBC - Gravel Footings
Dik
RE: ACI supersede IBC - Gravel Footings
Great feedback on everything. Focuseng had the right product that we are dealing with. It is a precast concrete wall beneath the wood sill plate that rests on a trench filled with gravel that they call a gravel footing. From what I have learned, Superior Walls licenses their product to individual suppliers who are responsible for their own engineering/installation data. It would seem then that some suppliers rely strictly on what is proposed in the codes and some, like who we are dealing with, apparently think their product is 'superior' to the codes (pun intended).
While I was out, it was decided that they would continue along the track of using this product. We are not going to specify it at all though nor are we going to approve it in any way. If they (contractor) choose to install this product, they must negotiate with the owner directly to find another EOR and we will absolve ourselves from it. We will provide a complete design based on what we believe in and it's completely on the owner to choose which route he proceeds with.
PE, SE
Eastern United States
"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi
RE: ACI supersede IBC - Gravel Footings
Mike McCann
MMC Engineering
RE: ACI supersede IBC - Gravel Footings
PE, SE
Eastern United States
"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi
RE: ACI supersede IBC - Gravel Footings
It always turns into a mess and a bunch more liability for the EOR. The savings are not likely what they think when all is said and done.
RE: ACI supersede IBC - Gravel Footings
I recall that there is language at the front of the IBC which recognizes the engineer's latitude and prerogative for alternate methodologies, materials, standards, etc. I don't recall the red tape involved in exercising this however.
RE: ACI supersede IBC - Gravel Footings
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Tony Krempin, PE
TopKnot Engineering
RE: ACI supersede IBC - Gravel Footings
Excel...I know what you mean. Value engineering certainly doesn't apply to how the EOR views it.
PE, SE
Eastern United States
"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi