Easy foundation work or a trap? 1

[ANE91]

Local contractor sells underpinning services to homeowners. Jurisdiction requires a sealed engineering report before issuing a permit for the work. Their last guy retired; I’ve seen his work. Enter me: seems like a good potential source of revenue, low hanging fruit. Totally new line of work for me (though I’ve done basement wall repairs). Salient assumptions below:

1. No geotech report, but I could default to the lowest presumptive soil bearing pressures in IBC 1610 and 1806.
2. Contractor specializes in helical piers side-mounted to footings.
3. Contractor is likely promising to “fix the foundation” when they really mean that they’re arresting or at least attenuating settlement. No jacking applicable.
4. Loads are not high enough and walls aren’t long enough to warrant special attention for any eccentricity.
5. I cannot think of any codified reason for the jurisdiction’s requirement beyond the basic alterations stuff in the IEBC.
6. By and large, these aren’t life safety issues but rather serviceability concerns. I would pull in a geotech for a house that looks like it’ll disappear into a sinkhole or some such.
7. My reports would simply verify whether the contractor’s proposed underpinning sufficiently increases the bearing surface so as to justify an expected decrease in settlement, even though the house is probably done settling by the time they get involved…

The last point doesn’t 100% sit right with me. On the one hand, who am I to tell a contractor what he can/cannot sell? On the other hand, I doubt that I would find much of that work truly necessary. Would getting involved make me party to deceit?

As much as I like to make money, I hate trouble more. Can I get a sanity check on this, particularly from others who design underpinning? Feel free to tear me a new one; I can take it. Thanks.

 

[XR250]

For better or worse, I do a fair amount of these. The AHJ requires an engineer design and "sign off" post construction.
It is basically showing helical piers every 5-6 ft with the footing notched out for the bracket. For sign-off, we use photos and the boring log showing install pressures that can be equated to capacity. Pretty much standard practice in my area so I am not being too much of a cowboy.
The foundation company provide a lifetime warranty so the risk is a bit mitigated. Have not had an issue in 20 years.

 

[Greenalleycat]

@ANE91 not sure about this comment specifically that you've made:

"On the one hand, who am I to tell a contractor what he can/cannot sell? On the other hand, I doubt that I would find much of that work truly necessary. Would getting involved make me party to deceit?"

No one is telling the contractor that they can't sell helical piles, or sell their services using said piles to relevel/stabilise foundations
However, assuming you were working in my country at least, the law dictates that they can't just cowboy their way through it
They are doing work to a house and there are performance standards set by the Building Code that they must comply with
Some of these relate to workmanship (their domain) but others require designer input
Does your contractor know the bearing demands? foundation strength? soil profile? - that's where you or someone else comes in

So it's not telling them "what they can sell": it's working with them to use their product to deliver compliant building work

 

[jerseyshore]

I think one key thing that a few people mentioned here is jacking vs securing. Jacking a foundation is a totally separate service/ approach IMO. That is very rare around here and needs careful consideration. Geotech is a must and a thorough analysis. I usually only see those done w/ push piers, never helicals.

And I think there's a big difference between doing actual engineering on the repairs vs a report/ rubber stamping what a contractor puts together.

I never consider the the latter, but see a lot of work that those other companies/ engineers do. If we do site visits on 95% of the projects, those guys rubber stamping a title page for the contractor might do 10% or less. They are so disconnected from the projects that when something goes wrong (and it does quite a bit) they have no clue what the problem even was in the first place.

 

[Greenalleycat]

@jerseyshore yes I agree there are some differences but you still need to be careful even if you're just "securing".

Your assumption has to be that the foundation is point supported at the pile locations as the existing soil has shown itself to be inadequate to provide support (why else are you doing this?). You then need to check the as-built foundation for its ability to handle its Ultimate design loads (1.2G + 1.5Q, G + Eu, G + Wu, whatever) assuming that it is pointed supported.

Critically, there is always an eccentricity with this. I've used helical piles before, there's no practical way to get them central under the foundation. So not only do you have your Ultimate loads going onto the existing foundation as a spanning member instead of being fully supported, now you're sticking a wopping great torsional moment into the foundation. And, having extensively looked at this myself on some existing foundations, there is no real system to resolve that torsion without putting in new foundation beams.

 

[jerseyshore]

@jerseyshore yes I agree there are some differences but you still need to be careful even if you're just "securing".

Your assumption has to be that the foundation is point supported at the pile locations as the existing soil has shown itself to be inadequate to provide support (why else are you doing this?). You then need to check the as-built foundation for its ability to handle its Ultimate design loads (1.2G + 1.5Q, G + Eu, G + Wu, whatever) assuming that it is pointed supported.

Critically, there is always an eccentricity with this. I've used helical piles before, there's no practical way to get them central under the foundation. So not only do you have your Ultimate loads going onto the existing foundation as a spanning member instead of being fully supported, now you're sticking a wopping great torsional moment into the foundation. And, having extensively looked at this myself on some existing foundations, there is no real system to resolve that torsion without putting in new foundation beams.

Helical piles w/ underpinning brackets onto notched footings get the load as close as possible to concentric for retrofit conditions. When we have heavier loads or special conditions we'll try to alternate pile installation on both sides of the wall.

I will say that these helical piles, especially for repair/ retrofit conditions have mostly been installed around NJ since hurricane Sandy in 2012. I've seen very few issues with them besides the occasional contractor who cheaps out and only drills them 7 ft deep or something. Will be interesting to see how they hold up over the years.

 

[Ron247]

Absurdly common in Texas. Ask me how I know...

If you are working in Texas, from what I have heard, you have an endless supply of potential work. Swelling soils are one of the main sources of helical anchor usage typically.

I would stay away from side-mounted. I worked a legal case where they did not chip back the concrete. The put the shelf of the anchor under the foundation, but it was on the outside edge, about 1' from the crawl space block wall. All they wound up doing was leveraging the foundation over and almost buckled the crawl space block wall. I excavated the entire rear of the house to show the anchor locations. This also exposed one of the cons the contractor used. Charged for 15 anchors, installed 12. But worse than that, they were charging for extra 7' shaft length beyond the 14' estimated. All of them took from 3-5 extra shafts, including the 3 they never installed. They had a sketch showing each location and the extra shafts.

I have never designed an underpinning project where I gave any kind of guarantee ESPECIALLY on expansive soils. I explain to the client up front that in essence, the house was built on soils that were not suitable for construction. There are original designs and repairs that can minimize the issues related to poor soils but cannot eliminate them nor get them to a universally accepted level of performance. If they do not like me putting a disclaimer on my design, I walk away from the job, but they know up front.