Foundation/Helical Pile Contractors

[TRAK.Structural]

Anyone here do work with residential foundation contractors who install helical piles and other foundation repairs? Recently I've been asked to "approve" a recommended repair scheme that was put together by one of these types of contractors. This is part of a real-estate transaction so my info has come solely from a Realtor at this point and I do intend to reach out to the contractor but I am curious how engineering consultants go about working on stuff like this. Is it as simple as calculating the applied loads in the affected area and verifying that the published capacities of the pile products can resist the loads? Would you want to observe the installation of the piles and verify measured installation torque matches the spec.? Do you typically check dimensions of the footing after it is uncovered to verify that it can span between piles? What are the major pitfalls in being the consulting engineer working to verify these types of repairs are adequate?

I use the word "approve" in the above loosely so let's try not to get hung up on what constitutes being in responsible charge etc. etc. My intent, If I take the job, would be to perform the actual engineering myself just like when I design new structures from scratch.

 

[dik]

I generally just spec them and provide the design loads. The helical pile supplier provides the sealed design.

On one project in Saskatchewan, I designed the helical piles based on information provided by the geotekkie. It was a transformer pad with six 400,000 lb transformers... my first helical pile design.

 

[XR250]

The AHJ requires us to write a "closeout letters" for our underpinning designs. We just base it off pictures and boring logs/torques.

 

[SE2607]

Anyone here do work with residential foundation contractors who install helical piles and other foundation repairs? Recently I've been asked to "approve" a recommended repair scheme that was put together by one of these types of contractors. This is part of a real-estate transaction so my info has come solely from a Realtor at this point and I do intend to reach out to the contractor but I am curious how engineering consultants go about working on stuff like this. Is it as simple as calculating the applied loads in the affected area and verifying that the published capacities of the pile products can resist the loads? Would you want to observe the installation of the piles and verify measured installation torque matches the spec.? Do you typically check dimensions of the footing after it is uncovered to verify that it can span between piles? What are the major pitfalls in being the consulting engineer working to verify these types of repairs are adequate?

I use the word "approve" in the above loosely so let's try not to get hung up on what constitutes being in responsible charge etc. etc. My intent, If I take the job, would be to perform the actual engineering myself just like when I design new structures from scratch.

I've done this type of work. In doing so, I have determined the capacities of the piles and have compared it to the demand. Here is a source:
www.ramjack.com/commercial/engineer-resources
In my cases (two story residential), the limiting factor is the capacity of the existing footing spanning between piles. One of the "issues" I've had with the specialty contractor is that, when they provide the capacities, they consider the load (applied at the centerline of the footing) to be concentric with the pile. For retrofit conditions, the pile is attached to the side of the footing with an "L" bracket. In my analyses, I apply an eccentricity, which obviously diminishes the capacity of the 2-7/8" diameter pile shaft. Still, the limiting state is the capacity of the existing footing to span between piles. IIRC, I don't get/need much more than 15k (ASD) on each pile even though the contractor claims a capacity of ~50k.
I also get pile logs and compare them with the demand.
HTH

 

[dik]

I understand that in a given area there is a close correlation between the installation torque and the load capacity.

 

[XR250]

I've done this type of work. In doing so, I have determined the capacities of the piles and have compared it to the demand. Here is a source:
www.ramjack.com/commercial/engineer-resources
In my cases (two story residential), the limiting factor is the capacity of the existing footing spanning between piles. One of the "issues" I've had with the specialty contractor is that, when they provide the capacities, they consider the load (applied at the centerline of the footing) to be concentric with the pile. For retrofit conditions, the pile is attached to the side of the footing with an "L" bracket. In my analyses, I apply an eccentricity, which obviously diminishes the capacity of the 2-7/8" diameter pile shaft. Still, the limiting state is the capacity of the existing footing to span between piles. IIRC, I don't get/need much more than 15k (ASD) on each pile even though the contractor claims a capacity of ~50k.
I also get pile logs and compare them with the demand.
HTH

We make them chip the footings flush with the foundation wall to limit eccentricity. Honestly, i don't even calc the footing capacity unless it is obviously going to be a crap one. Standard of care around here is install them 5-6 ft, O.C. and figure out the load based on that. These things have a bit of voodoo to them as I don't know how they calc out at all with the eccentricities involved but they seem to perform well. When they don't, the contractor just comes and tightens them up. That is what a lifetime warranty gets you.

 

[SE2607]

We make them chip the footings flush with the foundation wall to limit eccentricity. Honestly, i don't even calc the footing capacity unless it is obviously going to be a crap one. Standard of care around here is install them 5-6 ft, O.C. and figure out the load based on that. These things have a bit of voodoo to them as I don't know how they calc out at all with the eccentricities involved but they seem to perform well. When they don't, the contractor just comes and tightens them up. That is what a lifetime warranty gets you.

5-6 feet span of an existing footing is about what I get analytically.

 

[XR250]

Don't forget to take into account some arching action of the foundation wall if it ain't too beat up.

 

[TRAK.Structural]

Dik - When you say the "supplier" are you saying the contractor provides a sealed design for the piles themselves, or they have the pile manufacturer provide a seal?

XR - do you typically have some test pits dug first to determine if its going to be a "crap one" by looking at its condition/size?

SE2607 - For 2-story construction do you require cutting drywall/ceiling to figure where the load bearing elements are so you can track the load down? For 1-story stuff I think conservative assumptions work fine but could see that getting out of hand for larger homes.

 

[dik]

When you say the "supplier" are you saying the contractor provides a sealed design for the piles themselves, or they have the pile manufacturer provide a seal?

The helical pile supplier, hired by the general/foundation contractor.

 

[XR250]

XR - do you typically have some test pits dug first to determine if its going to be a "crap one" by looking at its condition/size?

No. If it is pier and curtain wall sitting on a bed of mud, usually we will just call for replacement of the wall/footing. Otherwise, the contractor lets us know if it looks bad when they start digging.

 

[SE2607]

SE2607 - For 2-story construction do you require cutting drywall/ceiling to figure where the load bearing elements are so you can track the load down? For 1-story stuff I think conservative assumptions work fine but could see that getting out of hand for larger homes.

No. In my cases, I'm pretty certain the load bearing elements are 2x4 (nominal) studs, so I put the c.g. of the wall load 1-3/4" from face of footing. I also assume the existing footing is 12" wide and place the c.g. of the footing 6" from face of footing. I also assume the fixity condition at the top of the micropile shaft is guided (allowed to deflect, but not rotate). The bracket connecting the micropile shaft to the footing also has eccentricity. Without going back and looking at my calcs, I believe I essentially have a 5"-6" eccentricity.

HTH

 

[gte447f]

TRAK, some good feedback has been given so far based on the experience of other posters, but I think you can gather from the information provided that helical pile underpinning for residential foundations is a bit of a mixture of wild west installation contractors doing it their way and a bit of magical voodoo engineering when required. Where I practice, helical pile underpinning of residential foundations is almost always done without the involvement of any engineering.

In your situation, I would first focus on your relationship to the various interested parties. You mentioned that this project is related to a real estate transaction. Be careful, because that has the potential to get messy if the buyer is not satisfied after the sale and decides to blame the foundation. First, don't deal with real estate agents. They are supremely skilled at wasting your time, and they ultimately will not be your client. Would you be working for the buyer or the seller or as a design-build subcontractor for the foundation contractor, and if so, which party would they be working for?

 

[TRAK.Structural]

GTE - I'd be working for the buyer in this scenario. I think this is the way the foundation contractors prefer also.

I know that helical piles (especially products used in the residential market) aren't good for much lateral. In the case that piles are used to prevent worsening settlement, seems to me that some amount of lateral resistance from the piles may be needed if the friction resistance from the old footing to the soil is essentially null in the areas of the new piles. Is it common practice to calc out the required resistance or are folks rationalizing somehow that the piles only take vertical load?

 

[gte447f]

I think in most cases of of residential underpinning, in general, the piles are assumed to carry only vertical loads and are "designed" that way. I am not aware of any other design or construction actions intended to provide lateral resistance to offset a theoretical reduction in lateral resistance from reduced foundation friction. I think any such phenomenon is considered negligible.

 

[gte447f]

And yes, I think engineer and contractor both working separately for the buyer is probably the most favorable scenario.

 

[dik]

I've spec'd small lateral loads occasionally... accommodated by the helical pile engineer. It doesn't usually affect the helices, normally only the shaft slightly. They are normally small dia tubes and may need to get a little larger to accommodate the soil lateral and the lateral induced moment,

 

[dflva]

If this exercise is for pricing, I think the Contractor and the Engineer could work for the buyer. If the objective is to perform construction at the property, the Contractor can't work for the buyer - he doesn't own the property!

 

[gte447f]

If this exercise is for pricing, I think the Contractor and the Engineer could work for the buyer. If the objective is to perform construction at the property, the Contractor can't work for the buyer - he doesn't own the property!

Good point dflva. Contractor and engineer could both work for buyer after closing if buyer and seller could negotiate based on cost of repairs. Otherwise, contractor working for seller and engineer working for buyer might work, but it sends up a red flag to me as setting up an adversarial relationship from the get go, because the interests of the engineer's client (i.e. buyer) and the contractor's client (i.e. seller) are not aligned. Both could work for the seller, but it carries the risk of the buyer being unhappy with results after purchase and looking to hold engineer responsible.

 

[TRAK.Structural]

Right now it's just an evaluation to see whether or not underpinning is needed. If it turns in to full design that would be after the home sale is complete.