Pouring concrete underwater

[8NTX]

I need to add a couple of piers to the front (shallow end) of my boat dock. The water at this location is only about 2 ft. deep. I plan on using treated 6" posts, set in concrete. The bottom is soft mucky sand. I have an old-fashioned "twister" clamshell posthole digger to use. I will probably put a carboard tube form down; hopefully finding one at least 5 ft. long to get to the top of the water. But no doubt, the water will seep into the hole as quickly as I can pump it out. I've heard there is an additive to put into the concrete mixture to ****** washout and bind the mix together, but can't find it. Anyone have experience or advice here?

 

[BigAl]

I did the same thing to my dock about 10 years ago . My concrete columns are about 4 feet tall and 8" in diameter . The deeper you can go the better for side support . Try to dig down to firmer soil it possible . Otherwise try to widen out the footing support so you end up with a larger support bearing area . Use a "Burk Tube" to place the concrete in . They come in several diameter sizes and lenghts . Most larger lumber yards have then . I also drove down 4 pieces of #6 ( 5/8") rebar for added support . You want to use "Plastic" cement and it is also avalible at all lumber yards.I also made a X brace for the columns to give it more side support . Just put a 1/2" x 10 " anchor bolts through the side of the "Burk Tube" where you want the X braces to tie across to the colmuns at . Don't forget to have the Burk Tubes braced real well before you start pouring in the concrete . Use a piece of left over rebar to vibrate the concrete down and to remove any trapped air bubbles or water as you place the concrete . Keep the concrete really thick and not to wet !!! The water will be chase out as you keep adding concrete . Use at least a 3000 lb. mix or 6 sack mix . Don't forget a 1/2" x 10 " anchor bolt on top to attach your post beam brackets too ! Then leave it alone for at least 7 days so it can cure slowly .At 28 days it will have about 80% of its final strenght . I left the Burk Tube shell on and did not even worry about cutting it off .Its been 10 years with no problems for me so far! Good Luck ,Big Al

 

[BXMMCC]

If you have a high volume low pressure water pump, you can waterjet the poles in without using concrete. That's how pilings are installed in the Chesapeake Bay area, and also on the New Jersey sea coast. To make yourself a believer, get an old garden hose without an end fitting, turn the water on, then work the hose down into muck at the bottom of the pond. Work a 2x2 into the hole where the hose is putting out water. keep shoving both down into the bottom. Shut the water off. Have drink of iced tea. Try to pull the 2x2 out!

 

[Renze]

About 10 years ago, our family has changed the small cow fences, a small pole every 8 to 10 meter, with a barbed wire, for a good horse fence with big 12 x 180 cm poles every 4 meter, with two smooth 3 mm wires and a rubber belt.

i think it totaled about 4 km of fence. We have waterjetted all the poles, with a manure tanker filed with water. We had a 10 meter hose on it, a 3" hose, with a metal jetpipe on it. The poles sticked very well, the work was easy (dont wear boots as they will be filled with water very quickly..) and it is a very good job to do in a summer heat wave. It was the only job we could do in that heat.... /forums/images/graemlins/grin.gif

 

[greyskies99]

Find the above suggestions very interesting. Thank you. Have a steel pipe dock at lake where 4" pipe has been driven into bedrock, making a very strong structure for decking and docking. Unfortunately this method is also very expensive, and can only be done economically in the winter. Is a concrete filled sonotube a possibility? How would I anchor it to a rock lake bottom 2-5' deep? What diameter would be roughly equivalent to equal the strength of steel pipe? Will concrete tube resist ice pressures in the winter?

Thanks in advance for your help!

 

[AGGIE00]

You could use a cut out 55 gallon drum in that depth of water as a surface casing. Push it down into the mud and pump the water out. Then you have a dry are to work with pouring your piers. Waterjetting would be a lot less work and have plenty of strength for your application. You could also rent a backhoe and drive the pilings plenty deep.

 

[Johnp33]

Putting anything in water that freezes is a crap shoot, depending on how thick the ice gets, it can sheer off most anything also in the spring, when it starts thawing the wind direction can change and destroy everything.
We put a dock at a friend's place we dug two holes, about 10 ft apart, with a back hoe then filled them with cement and we had a ring on a float with a chain and it anckored, when the cement cured he has two chains on cinches keeping the dock in position, in the fall, we disconnect the chains and we pull it out. all that is left in the water is the ring and two links of chain.
We are going to pore an base for on the shore to using a 2 inch pipe and a home made hinge. 1/2 in the cement and 1/2 on the dock. Pull out the pipe and she is free to come out. giving it a more stable base.

 

[Groo]

I'd do some culvert or something similar instead of a cardboard tube as a concrete form, and have it sticking above the water line.

the water driven posts sound like a better idea though.

another option would be a tire filled with concrete and a metal post sticking out of that to support you dock. just toss it in and let it settle some before you tie it to the dock. Maybe make it so it could be adjusted as it settles some more.

 

[vtsnowedin]

Good discussion with some very good ideas above. Your not building the White House steps here so allowing for some future settlement and leaving yourself a way to adjust seems wise.
As to your concrete placement underwater question let me give you the highway and bridge construction version. When placing concrete under water the concern is not mixing in the water that is in the form. Extra water weakens the concrete and seams of mud and water create weak spots in the footer. Underwater placements are normally done inside a cofferdam. The 55 gal. drum would serve for this. Then they place the concrete either through a pump hose or through a funnel arrangement called a tremie. Both serve to get the fresh concrete (state spec. pump mix or deck concrete would be ideal) to the bottom of the form without splashing down through the water in the form. As it comes out the end of the hose it forms a bubble of concrete that expands to the sides of the form then begins to rise to the top. New concrete coming out of the hose stays inside the bubble and never contacts the water. As the pour progresses the hose or tremie end is pulled up to stay near the surface of the concrete but never pulled out of the bubble. When the surface of the concrete comes up out of the water you can scrape off some soggy concrete off the top leaving only good solid concrete behind once cured.
Bridge seals are often a thousand yards and involve thirty men two cranes and a concrete pump. How you rig up your small pour and get the same result is up to you.

 

[Egon]

http://courses.washington.edu/cm420/Lecture8.pdf

some information.

If it's on a lake that freezes over the chances are very good that one spring the concrete piles will either be displaced or sheared off.:thumbsup: