Questions about screw piles

[CANeng11]

Two questions about helical piles:

1. How accepted is the Torque Correlation method for designing helical piles?
2. For frost heave, is getting below the frost line enough for a screw pile or should you also check the uplift force due to adfreezing. One geotech report I saw recommended using 100 kPa over the surface area of the pipe in the frost depth to get the uplift force.

 

[Okiryu]

1. My experience (in Japan) is that helical pile contractors have their own data which correlates pile capacity vs. torque. This is based on static load tests. So, perhaps you can ask your local helical piles contractors if this type of data is available. Bottom line, without field load tests, torque data is typically accepted I my experience.
2. I would think that uplift forces will came from forces acting at the bottom of the pile cap. But better to check with your geotech.

 

[dik]

It varies somewhat with locale, but, there is a very good correlation of torque and load capacity... I'll see if I can dig up some literature on this... have a couple of papers stashed away.

Dik