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.

 

[phamENG]

When I first started on my own, I found myself in the opposite position quite frequently. I was called in after these companies came with their sales pitch. Always needed helical piers, house was always about to fall down. Usually it was a sagging floor joist or a structural bearing failure causing the framing to compress. Occasionally it was geotechnical, but usually a "meh, it's settled, might settle some more, but your house is fine - up to you if that crack is worth $45,000."

I'd stay away. But I don't much care for most of these companies.

As for the jurisdiction requiring engineering - it's probably for the piles. They probably want you to say the piles are up to supporting the load. That's another red flag for me. I'm not a geotech, and I don't have borings. Sure, the torque correlations are handy, but they're just that - correlations. What if they hit torque 3" above a lens - or layer - of soft clay? No way to know.

 

[Eng16080]

Their last guy retired; I’ve seen his work.

Was his work good or not so good? They'll likely expect the same from you (for the same fee).

In my experience, work like this tends to go to those sorts of engineers who are willing to throw a stamp on anything for a few hundred bucks. Maybe that's not so bad if you feel you can do this while still putting in an ethical amount of effort.

If I'm understanding correctly that this industry is a borderline scam, I would want no part in this.

 

[jayrod12]

We do this fairly regularly, but our typical underpinning consists of cast-in-place friction piles 25-30 feet long. The way we detail them with one of our repeat clients allows for jacking of the house to an extent. We've pushed some houses an impressive amount back to somewhat level. But none of our clients do the helical pile thing, probably because we don't want those clients. We're still a bit hesitant for helicals around here because it still ends up being an end-bearing foundation in highly plastic clay. The only benefit to helicals is that hopefully at the deeper bearing strata the moisture content of the soil is more consistent.

 

[JAE]

Most construction/design related lawsuits I've seen in my career involve single homeowners ticked off that their beloved house has problems and someone promised them something and it didn't meet their expectations.

 

[jerseyshore]

One of our biggest clients is a structural contractor who does a large amount of this type of repair work. As mentioned above, there are many many many shitty companies that do this type of work though, especially in my area. We have come across work for the other companies and always turn it down. The contractor we work with is very reputable and in NJ, an engineer must be on-site during any type of pile installation. So we are constantly in the field with the guys watching the installs.

For most residential work re-supporting 1950's foundations, basically anything is better than what was there. And all repairs require drawings here. No one would accept just reports. On bigger jobs, especially larger commercial repairs, we get geotechs involved first.

We aren't salesmen. Sometimes we'll go out to a job and recommend more piles to be installed (to the liking of our client) and other times say we can use less than they originally proposed (making them reduce their estimate). In 3+ years we've never had a problem with that side of it.

 

[JoshPlumSE]

I would say the work sounds good.... But, I think you may want to review their standard caveats on their contract documents. The key is what the contractor is promising. Is it to repair a settlement issue. Or, are they promising more than you would feel comfortable signing off on.

Also, of course, whether or not you'd be covered by their liability insurance.

 

[SE2607]

I've done a substantial amount of this work (i.e., more than one project LOL), always through the general contractor where the foundation firm was a sub contractor. The work I've done is in California, so I always get a geotech, not for the AHJs pleasure but for my liability (more lawyers here than building officials). The foundation sub, IMO, overestimates the capacity of the pile because they neglect the eccentricity of the load with respect to the centerline of the pile shaft. It hasn't made a substantial difference for vertical piles because, in my cases, the limiting factor was the capacity of the existing foundation to span between piles, but it's enough not to be neglected. The work I've done has been on 2 story residential construction built in the 70s or 80s. When I've analyzed the capacity of the existing footings, I've neglected the steel because I know, at best, there is only 1-#4 T&B which yields less flexural capacity than plain concrete. I develop tables for capacities at 5 foot incremental depths and specify the torque requirements based on the applied load and I require that BOTH the torque and specified depths are to be met, unless the pile meets refusal. In my cases, the failed foundations occurred, IMO, due to their proximity to the top of slopes, which was pretty common during that period. Therefore, I also had to consider slope creep which required tie back piles. For tie backs, if a pile hit refusal, I added piles that could achieve the required embedment because refusal in compression means nothing in tension. In determining the capacity, I used the Terzaghi equations. Care had to be taken to avoid installing piles under openings because, during jacking, that could blow out the windows. That never happened on my projects. To answer your question, yes on soils report, yes on calculations, drawings and details and very little of justifying the design based on a liberal use of "engineering judgement".

 

[TRAK.Structural]

To answer the original question:

Is it easy - Likely yes

Is it a trap - Likely maybe

I like the approach as described by @SE2607, putting in some upfront work to figure out allowable footing spans, incremental depth capacities, torque requirements, etc. This way you can check the contractors plan with your own work that you are presumably comfortable with, rather than just relying on what they have done in the past. The sticky part is that your approach could be different than what your predecessor did, and the contractor may not want to change and adapt to your new/different requirements. And as others have stated, it may be impossible to perform this work for the fees your contractor is used to paying.

If you are able to satisfy your own level of comfort and ethical duties all while being paid appropriately for your efforts than I think it's worth exploring.

 

[ANE91]

Incredible responses...thank you everyone. I have some more questions, please.

They probably want you to say the piles are up to supporting the load

All the load? The footings are already doing that and haven’t experienced a local/general bearing failure. Thank you for sharing your experience btw.

Was his work good or not so good?

I have his reports but no calcs. Can’t tell what he checked (or didn’t), so part of my goal here is to figure out what my "standard of care" is for these assignments. I get to decide how this goes forward, and the contractor understands that, thankfully!

We do this fairly regularly, but our typical underpinning consists of cast-in-place friction piles 25-30 feet long...in highly plastic clay.

Interesting...I'm assuming that you need to neglect the top 5ft or so of soil and need to mobilize a lot of skin friction for uplift?

Most construction/design related lawsuits I've seen in my career involve single homeowners ticked off that their beloved house has problems and someone promised them something and it didn't meet their expectations.

100%...not a question, just validating this statement

For most residential work re-supporting 1950's foundations, basically anything is better than what was there. And all repairs require drawings here. No one would accept just reports. On bigger jobs, especially larger commercial repairs, we get geotechs involved first.

The more I learn about NJ standard practice, the more I marvel at how lax other nearby jurisdictions are in comparison. I totally get resupporting a defunct foundation, but a ~30yo footing doesn't need that unless it was inadequate to begin with. There's the rub — how acceptable is it for an engineer to work off the assumption that the likely prescriptive footing checks out without digging test pits?

@SE2607's answer really drives home how this work can easily get out of hand. I've done enough SPT/CPT correlations to playact as a geotech for simple scenarios, but serious slopes and tiebacks are squarely outside of my competency.

the limiting factor was the capacity of the existing foundation to span between piles

If I'm understanding you correctly, then the footings don't work when asked to span because they were likely designed (or prescribed) for uniform bearing, correct?

 

[phamENG]

All the load?

Yes. Even if not jacking the foundations to get the house back to level, the installation process will usually apply an upward force on the existing structure. Load will transfer from the existing footing to the underpinning. The amount will depend on the type of underpinning as some use the building to push the underpinning into the ground, others don't. Trying to figure out how the load gets shared is a fools errand, though. Why are you there at all? If the piles are actually needed, it means that either the footing has failed or the soil below it has failed/settled. It may still be settling. If it is, then load will gradually shift from bearing to the pile as the soil continues to consolidate (or wash out if you've got water moving soil around). Unless you have lots of data tracking movement of the structure, it can be really hard to determine whether or not the building is still moving.

I've always been told not to mix foundation types. That's from other structural engineers and geotechnical engineers. One really sharp geotech once told me it is possible in certain situations, but they're rare and rarely worth the hassle.

So where piles go, I size the pile to take all of the load. Again, if they're needed as a retrofit, the existing is causing settling so the existing footing can't support the dead load and minimal live load that's there, and any future live load will go to the piles anyway as they'll be the stiffest path.

This assumption leads to SE607's issue - you now want footings that were designed as plane concrete, probably 8" thick, to span 6 to 10 feet between piles. No way that works for a light frame building. Masonry? Might be able to justify the wall spanning between piles, depending on configuration and openings.

 

[Ron247]

In #2, what do you mean by side mounted?
In #4, what direction is the eccentricity you refer to?

There are multiple nuances to look into before get into this. I have seen several anchor contractors use anchors for a problem that anchors cannot correct. As an example, a bowed 8” hollow block basement wall they then underpin as a correction.

I have seen several installed wrong. The installed anchors created a worse condition.

Another example is only underpinning part of a structure and leaving the balance to settle more than the underpinned area.

 

[phamENG]

Another example is only underpinning part of a structure and leaving the balance to settle more than the underpinned area.

I can second this one. House was settling, causing minor annoyances - sticking doors, really small cracks, etc. But the house was moving close to uniform.

The underpinned one half of the house but left the other half on spread footings. A 2 month drought caused the clays under the house and near the surface to shrink a lot, and the house cracked in half. Big rain storm shortly after refloated it, though....