Depth of bored piles in expansive soils

[SEARCH2016]

Understanding that the pile tip should be below the active zone (or depth of zero swelling?), how deep should it penetrate below the active zone to counter balance the uplift swelling pressures on the pile skin.

When I calculated based on soil's Su, the pile would have unreasonable depth and I wonder how engineering practioners calculate or estimate the depth. (Assuming that the soil along the pile depth has a unique Su value, for the sake of argument)

Thank you.

 

[EireChch]

Personally I've never calculated the uplift forces from expansive piles, however if the embodiment depth is excessive could you consider sleeving the pile through the active zone to reduce the embodiment depth?

 

[SEARCH2016]

Thank you for your response. True, one way to reduce the length of pile, is by a sleeve. But I would like to know if the calculation methodology gives a correct depth before prescribing a friction reduction sleeve. EireChch, if you have encountered a similar problem, may you let me know what rule of thumb method did you use? Thanks again.

 

[Retrograde]

http://australiangeomechanics.org/admin/wp-content/uploads/2015/02/G3_3.pdf

https://www.geplus.co.uk/Journals/2...nsion---a-simple-one-dimensional-analysis.pdf