depth of pile caps

huangyhg

depth of pile caps
should the depth of pile caps be below frost? i seem to remember that being the case but i can find no codes, standards or guides stating that to be the case.
it is not required and not necessary to have pile caps extended through the frost line. pilecap depth is usually determined by the anchorage depth requirement of pile dowels and anchor bolts. when the bottom of pile caps is above the frost line and overhanging from the piles, you need to put voidform underneath.
the most common thing to do is to have the bottom of the cap below frost depth.
what is typically done in my area (ct) is to place the bottom of grade beam below the frost line and the pile cap would be below that.  
as i've always understood it, if you're more than 450mm below ground level. frost action shouldn't be a problem (in gb). i can't see your pile cap being shallower thant that?
if you don't take it below frost line, what will happen?  you will have some uplift on your pile cap.  how much depends on the underlying soil properties (frost susceptible or not?, how far above the "design" frost line you are, source of water (water table) (if none, not a problem).  then taking this into account - can your system handle the expected uplifting loads?  practically speaking, endeng is right - pile caps are usually deep enough (at least a metre or more) that in most populated areas of temperate climate, you won't have to worry - go to northern ontario or northern alberta, etc. - different story.