Closed End Pipe Piles w/ Concrete Fill @ Top End Only

[PEinc]

My client is driving 100' long, closed end, pipe piles, approx. 24" diameter for a wharf. The plans call for the upper portion (about 20') of the pile to be concreted. Does anyone have any good reasons why or why shou;dn't the pile should be totally dewatered inside and below the concrete plug? If the pile is dewatered inside, there will be a very high water pressure on the outside of the pile. If the pile is allowed to have water in it below the concrete plug, the unbalanced water pressure on the outside of the pile will be minimal.

Any thoughts, warnings, known problems?

 

[DRC1]

We have done this before but I really don't like it. Eventually the piles will leak and fill with water, allowing corrosion in both faces. Concreteing all the way may cost a little more(generally not a lot in the whole scheme of things) but will give you a better product.

 

[PEinc]

If the pile is filled with water inside, there should not be much corrosion. There is little or no air and there will be no tidal fluctuation. This would be no different than an unfilled, open end pipe pie. Agree? I think there would be less corrosion potential if the pile is filled with water than with air. I agree that total concrete fill is better, but that won't happen for cost reasons.

 

[BigH]

John: Usually I have seen all pipe piles filled with concrete but not usually due to "capacity" requirements. Why don't you just use sand or gravel in the bottom part of the pile - then concrete up the top. If you are only concreting the top, how are you forming the inside formwork?

 

[DRC1]

PEinc.- Unless the concrete plug is poured below the water line, you will have som air, but if you don't have any tidal fluccuation, it probably isn't as big a problem. Since you do't have any tidal flucuation, I assume it is fresh water, which is significantly less corrosive. I was assuming this was in an ocean environment.

 

[PEinc]

There is tidal fluctuation but not as low as the bottom of the concrete plug. The concrete plug extend 25' below the bottom of the new wharf deck. Therefore, it is well below low tide.

I designed a L-I-P form for the concrete on a similar project for the same client. The form will hang from the top of the pipe pile. Because the pipe is closed end, the contractor will be able to dewater to a little below the bottom of concrete plug. Then, there should be little or no air inside the pile. The water in Port of Wilmington, DE should be fresh water. Occasionally, the salt line advances to Wilmington, but not often.

On Page 372 of Tomlinson's 4th Edition of Pile Design and Construction Practice, it says, Where hollow steel piles are plugged at their base with concrete or impervious soil it issometimes the practice to pump out the sea water and replace it with fresh water containing a corrosion-inhibiting compound. The addition of sodium nitrite and sodium carbonate to form a 2% solution can be used for this purpose. However, the need for this has been questioned because an empty or sea water filled pile contains little oxygen which is quickly used up in the early corrosion process, leaving none to maintain the corrosion." Any comments or disagreements?