Consider that all of the research work on the necessity of a cap plate that was done at Lehigh for H piles and did not consider this situation. You will have a condition that could exceed the bearing capacity due to the lack of confinement. It is not unconfined and it is not confined when considering bearing stresses.
Anything that you use as a plug will have to be restrained sufficiently so that the weight of the plastic concrete for the cap does not push the plug out and totally screw up the placement for the cap concrete. That would cost a lot of money in delays, removal and replacement.
If there is no cap at the bottom of the pile, the soil will move up through the open bottom of the pipe and there will not be much concrete required to fill the pipe. You may get some local settling of the soil that comes up through the pipe, but it will not be much. It would be the same settlement as if you drove an H pile. If you choose to add a plate plug at the top to save the marginal amount of concrete, the addition of the plate will likely cost more than the material cost of the concrete. But if you are dead set on providing a plug, make it out of 3/4" plywood. Drill holes for wire ties in the plywood. Wire the plug to 4 #5 rebar about 2'-6" long. Place the plug in the pipe with the rebar across the pipe. The rebar will keep the plug from sliding down the pipe.
Even with 21 24" diameter pipe piles, I doubt that you would save a yard of concrete with the plugs. With plugs, you will have at least one man day, 21 pieces plywood cut into a circle, plywood and rebar material. And you risk a local bearing problem at the pile to pile cap interface. If you could save a yard of concrete, that is $150. It is not worth it.
Fill the top of the pipes with concrete and save the cost and grief.
Regards, Harold Sprague
From: david@mdavidfinley.com
To: seaint@seaint.org
Date: Mon, 24 Oct 2011 17:52:33 -0400
Subject: RE: Steel Pipe Piles
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.
Thanks,
David
From: Harold Sprague [mailto:spraguehope@hotmail.com]
Sent: Monday, October 24, 2011 5:04 PM
To: seaint@seaint.org
Subject: RE: Steel Pipe Piles
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
From: david@mdavidfinley.com
To: seaint@seaint.org
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?
David Finley
M. David Finley, P.E., P.A.
2086 SW Main Blvd - Suite 111
Lake City, FL 32025
386-752-6400