Concrete Drilled Shaft Tip Elevations

[minorchord2000]

After determining the depth to fixity for concrete drilled shafts based on ADOT (Arizona DOT) Geotechnical Design Policy DS-3, how does one determine the tip elevation beyond the fixity depth? Is there a good rule of thumb (assuming that even exists) based on the shaft diameter?

 

[BridgeSmith]

The required depth is typically based on either limiting the deflection due to lateral load (usually determined by a P-y analysis with Allpile, Lpile, etc.) or by reaching the required axial resistance by end bearing, skin friction along the sides, or a combination of the 2. We haven't had much success with attempting to combine the 2 for most foundation materials, due to the severe reductions for one when combined with the other. It's much easier (and usually not much different) to use one or the other.

Rod Smith, P.E., The artist formerly known as HotRod10