Concrete pilings for a dock

[RobA]

I have a 2 acre pond I will be renovating this year. I want to add a dock before the job is done and the pond fills back up. I have looked at the different kinds of docks and would prefer a stationary one over a floating one. Rather than using pipes or wood pilings for supports I was considering concrete pilings. I would expect them to be about 4 or 5 feet tall (not including the footing) and about 10 inches in diameter. Anyone have any ideas on how to make them or if it is a wise idea? Sonotubes? Rebar?

 

[CurlyDave]

I have seen concrete pilings on commercial docks in the SF Bay.

They had spiral markings which made me think they were made using sonotubes. This location has several feet of tidal action, maybe +/- 5 ft so they were merely guides for a floating dock.

If I had to guess how to design ones for a small dock on a small pond, I would think about using something like a 12" auger on a PHD to get 4' below the bottom of the pond and then an 8" sonotube for the portion above the bottom of the pond.

I would reinforce it with 4 pieces of 1/2" rebar in about a 4" square pattern. A closed tie of 3/8" rebar should completely encircle the lengthwise pieces of rebar every 18" and at both ends.

Set galvanized post bases in the top to attach your dock to the top of the piers.

 

[EddieWalker]

I thought about doing the same thing CurlyDave described, but instead of 4 lengths of rebar, I thought I'd use three. Four just seemed too crowded. I also don't know if 1/2 inch is needed or 3/8's but in my plan, I was gonna use 3/8.

The biggest issue you will have is air voids in the pour. Either pour it real soupy, or make sure you knock everything down inside the tube real good. With all that rebar in such a small area, it will be real easy to get some massive air pockets.

Eddie

 

[RonR]

I can't comment on the concrete, but to me, it seems easier and likely cheaper to build a floating dock with it firmly anchored in concrete on the dry side.

For maintainability, if you needed to redo it, you could pull it out and work on it on the hard.

But I'm sure you have your reasons, so I won't try to change them.

ron

 

[CurlyDave]

...but instead of 4 lengths of rebar, I thought I'd use three. Four just seemed too crowded.

When I built my house, the engineer called out 4 pieces of 1/2" in a 12" round tube. 3 pieces might be good enough in 8".

I have a stinger (concrete vibrator) which assures a good fill no matter how crowded the bar gets. If you rent one, it is worth calling around to get one of the ones with a hexagonal head instead of the plain round ones. I knew the engineer who designed the hex ones and he claimed they were about twice as effective as round.

 

[cisco]

As per prior posts, a number of approaches will work, and you can add to the possibilities pre-formed concrete (with rebar) pilings that can be jetted into the muck.
Easiest method I've seen is to use plastic drain pipe (pick your color - white, black or blue), jetted deep and into position - which is not hard, and merely requires sticking the high pressure nozzle down the pipe -- and then filled with fairly wet concrete and a few lengths of rebar, agitated with some sort of vibrating device to break up air pockets. No soggy paper tubes, no concrete chipping, no major boat gouges from the rough concrete, and so on.
The guy I observed used 6 inch pipe for the walkway, and 8 inch for the pierhead. It's still standing (a decade, and 1 hurricane, later).

 

[RobA]

I was considering a floating dock but since the pond is going to be drained I was going to do stationary instead. I had seen on another website (pondboss.com; I'm sure you saw that one Eddie) where a pondonwer used 4" PVC filled with concrete and rebar for the pilings. I was surprised that 4" would be strong enough. I'm not so sure I like the look of PVC though. I also wonder if U/V wold eventually make it crack. I do not believe schedule 40 is protected from the effects of U/V light. I may just sink some 6x6 or 8x8 pressure treated posts instead. They look better, are easy to work with and should last a while.

 

[EddieWalker]

Hi Rob,

There was a discusion awhile ago here about marine grade preasure treated posts compared to the normal stuff we get at the lumber yards. I'd check around to see where you get it and what it costs before doing anything else.

I was real close to building a dock myself and had decided on the wood route. Of course, I wanted a sort of gazebo over part of it and several fishing areas on mine. The costs just kept adding up with limited return, which led me to building a peninsula and abandoning the dock idea.

As for the PVC for forms method, I'd just as soon use tubes for less money and greater size. I have no doubt PVC would work, but when comparing the price of each, the PVC just seems like an extra expense with no advantage.

Eddie

 

[RobA]

</font><font color="blue" class="small">( ( I'd check around to see where you get it and what it costs before doing anything else.)

Eddie,
I have about 6 months before I have to make a decision about what kind of dock I will build. I just like to check out all the possibilities. Nothing worse than doing something only to find out there was a much better way to do it.

Every time I look into different ways of doing a stationary dock I keep coming back to wood. I like the idea of marine grade pilings.

By the way, I do enjoy reading your posts and watching the progress of your project. You should be proud.