Pile foundations

[kabz91]

Hi all,
Im a fresh graduate and I want to clarify few things on pile foundations.
When casting piles the general practice is to cast piles first and do the excavation up to required depth later on. Why cant we first excavate upto required depth and do the piling from that level onward?

Thank You

 

[MotorCity]

It can be done both ways. Since you mentioned "casting", I assume we are only talking about concrete piles. If you cast the piles first and then excavate to the proper elevation, they will probably have to be cut off. Cutting concrete piles is a lot of work, especially if you have a lot of them. Also if you cut the piles, you will probably have to dowel in some reinforcement to provide a connection between the pile and structure above - again, its a lot of work. Deciding which method to use depends on the number of piles, depth of excavation, schedule, contractor experience, etc. The one advantage of cutting the piles is that its a lot easier to achieve a more precise top of pile elevation, but most of the time, the top of pile can usually be accurate within a couple of inches and its not a big deal.

 

[jayrod12]

Have you ever tried driving a piling rig around an excavation once a bunch of the piles are already poured? That's why they generally cast them first. It's generally easiest to do from grade surface, nice and flat with minimal obstructions to drive around. A good piling contractor can hit the final t/o pile elevation within a reasonable tolerance as long as it's not too far below the drilling surface.

 

[StructuralAddict]

The top layer of the pile is weak as it contains a considerable percentage of impurities that rise to the top while casting. Therefore, it is always better to remove the weak top layer of every pile.