As clarification, the pile is definitely not a displacement pile. We are using an open-end cutting shoe and the piles will be installed by vibrating them down as much as possible and then driving them the rest of the way to the required capacity. We do not need to fill the piles for additional strength - the pipe pile itself has ample strength. However, something needs to fill the interior of the pile or else the footing concrete will obviously go down the pile when the footing is cast. After the footing concrete is set, it does not matter if the interior fill of the pile settles - all of the footing load will be transferred directly into the pile itself through bearing. The fill inside the pipe is needed only to act as a form to avoid the added cost of pouring concrete down a hole. There are 21 piles in the footing, so it adds up.
I expect that that the pipe pile will plug at some point. And we will be preforming through a dense upper layer, so the elevation of the top of the plug will probably vary.
So my question is really limited to the top of the pile where a "void" within the pile may occur. There is certainly nothing wrong with having a reinforced concrete plug at the top of the pile, but I am trying to see what the industry typical practices are.
In the words of Thales of Miletus (6th Century BCE Greek Philosopher), "εξαρτάται". ....."it depends". ......OK, I just made that up. Thales was real; the quote was not, but I am sure that he thought it at one point or another.
But in response to your inquiry, it depends on if you are using the pipe pile as a displacement pile or not. If there is no end cap, then it is not a displacement pile. Generally, pipe piles are installed as displacement piles with an end cap, and while placing the concrete for the pile cap, the pipe is filled with concrete.
This is the font of wisdom that is put out by the FHWA. http://www.fhwa.dot.gov/engineering/geotech/library_listing.cfm Scroll down to "Design and Construction of Driven Pile Foundations". The download was prepaid by your taxes.
If you fill it with sand, you then need to ask if you need to compact the sand. And if you need to compact the sand, how are you going to compact it and test the compaction. I am lazy, I will fill it with concrete, vibrate it, and test the cylinders in a lab.
Regards, Harold Sprague
Date: Mon, 24 Oct 2011 12:18:06 -0400
Subject: Steel Pipe Piles
I have a bridge footing supported on 24" diameter steel pipe piles. The bridge is a grade crossing (no water) and the footing is below finish grade, so the piles will have lateral support from the soils for their full height. The piles do not experience any tension.
Is it typical practice to provide a reinforced concrete plug at the top of the pile? Or just sand fill?
M. David Finley, P.E., P.A.
2086 SW Main Blvd - Suite 111
Lake City, FL 32025