Frost Adfreeze for Screw Pile Design

[CANeng11]

I am designing piles for a ramp, roughly 5 kips factored load, without a geotech report. I am wondering if I should be using frost adfreeze for uplift calculations? I've seen values of 65 kPa to 100 kPa for adfreeze on the shaft perimeter in the depth of frost.

 

[EireChch]

I think your main problem is that you are designing piles for a ramp....without a geotech report.

5 kip = 24kN. That is a lightly loaded pile. That being said i would still be very concerned without a geotech report.

What geology are you in? Are the soils silty? Do you know where the groundwater table is?

 

[PEinc]

I would never call for helical piles without a geotech report or borings (or experience in the immediate area). Rock, cobbles, boulders, hard clay? Low design loads mean small helical materials which could be damaged easily in difficult ground conditions.

http://www.PeirceEngineering.com

 

[CANeng11]

I was planning on using the torque correlation method for design. If I reached the required minimum torque for this load (I would actually bump it up to 10 or 15 kip minimum) wouldn't that mean I have the achieved required capacity? From what I understand, the torque method is based on empirical data from the piles loaded in tension and the values are conservative when used in compression. I also apply a 0.4 reduction factor to the capacity of the pile for additional factor of safety.

 

[Okiryu]

Suggest to at least get some soil boring data of the site based on PEinc’s concerns. It will help you also to choose the size of the helical piles. Also, I guess that the contractor has historical torque-resistance data for similar soil conditions you are dealing with,otherwise the torque - relationship you are planning to use may be useless.