Helical Pile Shafts

[TDAA]

This is not project specific, but a request for opinions.

I have been working with a structural engineer that has expressed his dislike of helical piles. His concern is this: He feels the auger going through the soil disturbs it, leaving the pile shaft "unsupported". He worries that the relatively thin shafts would then be subject to buckling, especially if there is any sort of lateral load.

Obviously, this system has been used extensively, has been load tested under various conditions, and has been givin allowable capacities

I have my thoughts on the subject, but thought I would get a more broad opinion. The main topic involves the soil disturbance/bucling issue, but other opinions concerning helicals are welcome. Thank you for your input.

 

[PEinc]

A. B. Chance Company has a 1992 Bulletin 01-9203, titles Buckling Calculations. The Bulletin Quotes Bowles' Foundation Analysis and Design, 1st Edition, page 513: It is usual in design of piles to neglect L/r considerations for piles embedded in any type of soil since very little lateral support is required to avoid buckling."

ADSC (Association of Drilled Shaft Contractors recently had a study done by Allen Cadden and Jesus Gomez of Schnabel Engineering. The study concerned buckling of relatively small diameter micropiles. Check the ADSC web site. I think their paper is available there.

 

[eric1037]

According to the manufacturer's, there can be a concern with helical piles in very soft soils. To avoid this, the helical pile can be grouted, but this usually negates the cost-effectiveness and another deep foundation system becomes more economical.

 

[eric1037]

The rule of thumb is that if the N-value is less than 3 to 4, then grouting of the shaft whould be performed.

 

[slipstick50]

We use helical piling alot in our projects and when installed per the manufacturer's instruction, they work great,, the pile cap and its anchorage to the pile shaft is critical so don't skip there.