Precast column with chamfered ends - load transfer into piles

[Drapes]

Looking at top-down construction with precast plunge columns embedded into insitu barrette piles, with beveled ends to the precast cols where it transitions into the piles - refer below sketch reinforcement not shown for clarity.

Wondering if the chamfered cold joint would create any local horizontal splitting (tensile) forces within the pile (as shown in blue), or if the passive soil pressure around the pile could be relied on to resist this "thrust", or if I am overthinking it and the load transfer would be no different to a conventional column-to-column detail with horizontal cold joints created by the slab in between?

 

[RPMG]

I have not encountered this situation, but my initial response is that the ties should be designed to resist the hoop force, which is represented by your horizontal blue line.

 

[jayrod12]

Agreed, I think there is naturally going to be some splitting and you should have some ties to resist it. Should usually have ties at the top of the pile to resist the bursting stresses anyway.

There's not much passive pressure at the top of the pile either. In fact we usually get told that as the soil near the top of the pile dries out, it shrinks away from the pile. So you might be 3-500mm before you have competent passive pressure developing.

 

[Drapes]

Thanks RPMG and jayrod12, I suspected that would be the case.

However the loads in the columns are quite high circa 16000kN, so each half of the column (represented by the 2x topmost blue arrows) would transfer 8000kN at the chamfered interface, which would be equivalent to a horizontal splitting force of 8000kN if we assume a 45 deg diagonal strut angle, however would be difficult to provide enough tie reinforcement locally at the top of the pile to resist this force. How would you approach this?

If the piles are 30 to 40m deep, could you assume a near-vertical strut angle in order to reduce the splitting demand, or perhaps justify distributing the tie reo over a greater depth instead of locally at the top of the pile which would lead to quite a bit of congestion?

 

[jayrod12]

1:1 seems high for the chamfer, perhaps discuss with the supplier, limit it down to something more manageable. I've never seen that sharp of chamfers, normally it's quite nominal just to facilitate proper consolidation at the bottom of the form and ease of formwork removal.