Helical piles - contractor designed vs. specified 1

[cec17]

I am wondering about the process for designing or specifying helical piles for new construction, as a deep foundation element. Typically, with micropiles, we will have the contractor use a geotechnical report geared toward recommendations for micropiles and they sub out the specialty micropile design to another specialty sub.

Is the process for having "contractor designed" helical piles typical as well? Since they are more 'proprietary' it seems like a supplier, such as CHANCE, could do the design when they supply the helicals. Alternatively it seems more straight forward to just spec a required torque (and load), and perhaps an estimated depth using CHANCE software, for bid purposes.

From my perspective, it seems like requiring the contractor to retain a specialty designer for helical piles would be unnecessary since there are so many resources and design tools now (provided you have good soil data). Maybe I am over-simplifying it.

 

[ANE91]

Many reasons to engage a registered design professional for helical piles (colloquially referred to as “screw-piles” or “helical piers,” in my market).

I own a hard-copy of Perko’s book on the subject. It’s ok, if not a bit overhyped. He discusses the shortcomings of torque criteria. His book can answer your question in more detail.

There’s nothing inherently wrong with the manufacturer/supplier providing their own design, but it should probably be verified by an EOR for general compliance with the building specifications.

EDIT: For the record, I’m a big fan of design going the “prescriptive” or “tabulated” route such that non-engineers can do it. (Contentious, I know.) This frees up SEORs to work on more complicated stuff.

 

[cec17]

Thanks @ANE91. Good info, I will try and get a copy.

In this case, I would be the EOR. I guess I'm leaning more toward adding the pile load requirements, and calling it "supplier-designed" in lieu of contractor designed. Not sure if that's typical, but it seems it might get the job done.

 

[phamENG]

My preferred process is this:

1. Geotech does borings and generates a report. They provide estimated depth and allowable load for various bearing plate (helix) sizes.
2. I design the building and determine the optimal pile layout based on the geotechnical engineer's guidance.
3. I write a specification for the helical piles listing estimated depth, required allowable load, and any other pertinent information. I also ensure they get the bearing logs and are aware of any fluid soils that are unable to brace their piles (which can be a real problem around here). This allows the helical pile contractor to provide an accurate estimate of the cost while also ensuring we get piles in line with the geotech's recommendations and not just what the pile contractor feels like or has extras of in his shop.
4. Helical pile contractor provides a submittal proving that their chosen pile meets the necessary requirements.
5. Special inspector monitors pile installation and provides depth and torque logs.
6. I check it to ensure the depth is in line with the geotech's recommendation and the torque correlations meet the capacity requirements.

 

[jerseyshore]

My preferred process is this:

1. Geotech does borings and generates a report. They provide estimated depth and allowable load for various bearing plate (helix) sizes.
2. I design the building and determine the optimal pile layout based on the geotechnical engineer's guidance.
3. I write a specification for the helical piles listing estimated depth, required allowable load, and any other pertinent information. I also ensure they get the bearing logs and are aware of any fluid soils that are unable to brace their piles (which can be a real problem around here). This allows the helical pile contractor to provide an accurate estimate of the cost while also ensuring we get piles in line with the geotech's recommendations and not just what the pile contractor feels like or has extras of in his shop.
4. Helical pile contractor provides a submittal proving that their chosen pile meets the necessary requirements.
5. Special inspector monitors pile installation and provides depth and torque logs.
6. I check it to ensure the depth is in line with the geotech's recommendation and the torque correlations meet the capacity requirements.

This is ideal, but unfortunately I only get a geotech report for 50% or so of new residential projects.

Usually for helicals I put some standard Chance notes and specify the allowable and ultimate loads. It's on the contractor and on-site engineer to develop those capacities.

 

[phamENG]

50% or so of new residential projects.

Then you're doing better than me. But if there's piles, I don't budge. If you want me to design a house on piles of any kind you'll get a geotech report or I'm out. Full stop.

 

[jerseyshore]

Then you're doing better than me. But if there's piles, I don't budge. If you want me to design a house on piles of any kind you'll get a geotech report or I'm out. Full stop.

We are probably the most pro-geotech report company in the whole area and it's a struggle. Most houses are built with nothing more than a boring from a well company. And the only reason it may be 50% of new houses give us reports is because we recommend a local geotech so much.

I don't have a problem specifying piles when they ask for them. I do have a problem not specifying them when there's a possibility they are needed. I'll always hold firm for geotech report there.