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Small coffer dams?

Discussion in 'General Industry Questions' started by Orchard Ex, Jul 7, 2011.

  1. Orchard Ex

    Orchard Ex Super Moderator

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    I need to pour a small boat ramp dry. Has anyone built small coffer dams? Enclosed area needs to be about 35' out and 15' wide holding 4' of water at the deep end. Not looking for sheet pile, it only needs to last for a few days or so. What have you used in the past? It is in tidal waters and I'm wondering about leaving a section out until it needs to be dewatered, or maybe putting in a small section of pipe that can be plugged when needed so that the water can equalize as the tide moves in and out. I'm being told that it's easy by a lot of people who have never done it before. :rolleyes:
    Did I mention that it needs to be cheap too?:)
     
  2. willie59

    willie59 Super Moderator

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    Hmm, even just 4 ft of water is a lot of pressure, not sure how you'd do it without driving pile.
     
  3. grandpa

    grandpa Senior Member

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    Sandbag's man..... there known for holding back water..... prolly get a deal on some used one's around Minot N.D.
     
  4. Drc

    Drc Well-Known Member

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    In areas where farmers use flood irrigation the irrigation ditch dam consists of a 8' x 8' canvas with a sewn loop on one side, a 2" x 4" is threaded through the loop and the 2"' x 4" is laid across the ditch, the canvas sheet is stomped down in the ditch, the wieght of the water presses it against the contours of the ditch and one ort two foot canvas dam backs up the water.

    I've dammed up creeks by double thick reinforced plastic sheet laid over a heavy steel pipe or Wide Flange beam.

    If I've explained myself you got the idea, work with it, and maybe look up Porta dam on the or look for inflatable coffer dams.

    Good luck cuz Hell Yeah it can be done
     
  5. Orchard Ex

    Orchard Ex Super Moderator

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    I was thinking of a combination of sandbags with plastic sheet laid over and out on the wet side, similar to the porta-dam but without the nice structure that they have on the dry side to hold up the sheet.
    Anybody know about how steep you can stack sandbags? I mean, to hold back 3' of water does the base need to be 3' wide? 6' wide? I'm trying to get an idea of how many bags I'd need to fill/move/remove.
    BTW - I got an estimate for a porta-dam install... :eek: It does look like a nice system for a bigger project though.
     
  6. dayexco

    dayexco Senior Member

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    you can rent piling, if you're only talking a max of 4' of water, 10' 7 gauge panels will work...that's the surest bet.
     
  7. grandpa

    grandpa Senior Member

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    Rule of thumb... for every bag you go up, you have to go out one on the pressure side.
     
  8. stumpjumper83

    stumpjumper83 Senior Member

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    precast the contrete, and lay it on a bed of pea gravel like a superior wall, just underwater... You could also precast it, cut holes in the dry end for a couple of piers and anchor the slab in place that way.
     
  9. forestroad

    forestroad Active Member

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    Can you operate machinery in the water prior to dewatering?? If so will underwater surface support an excavator?? Gravel or silt??
    Tidal water exerts a lot of pressure even at only 4' deep.
    I can think of and have seen and done similar projects a number of different ways.

    In the Pacific Northwest where I am located a boat ramp would most likely be state or federal funded which double my labor costs as the contractor is required to pay prevailing wage. Because of this we have found that using machinery and innovation is more cost effective in the long run.
    Sandbags and plastic is cheap but 85 lineal feet of sandbags 2 to 5 feet high would require roughly 1.5 to 1 slope for support, thats a whole lot of sandbags to be placed and later removed. To me this option seems rather labor intensive especially considering that removing deepest sandbags would require laborers to squat into the water. If conditions allow and machinery can be used prior to dewatering, placement could be easily accomplished using an excavator with a skilled operator but removal would have to be done by hand, unless local authorities will allow the sandbags to be individually cut and emptied leaving only the empty sandbag to be removed??

    What about a combination of sandbags and sheet pile? Or sandbags 25' on each side, on the end you could fabricate a U shaped structure out of plate steel, cut the leading edges at an angle that allows the end sheet to be placed so that the top is slanted slightly in towards your work area. This would provide additional support and cause the pressure on the end plate to force the whole structure down. Could be placed with an excavator or crane, even floated to the end and anchored using weights prior to sandbag placement and dewatering. Once your structure is in place pump out the water and additional sandbags could be placed behind the steel structure for additional support if neccesary.

    Have seen large precast pads placed directly into water on short driven piles, small casons only used to cut excess piling and fasten piles to pads. [not sure how fastening was accomplished]

    Friend of mine rented crabpots from local fisherman, filled the crabpots with sandbags, plastic on the outside and placed them all with an excavator. When he was done just dumped out the sandbags into his dumptruck, took em home and biult a giant sanbox for his kids. I didn't think crabpots could handle the weight but they worked like a charm and he did the whole project entirely by himself.

    I myself have used large 3'x4' concrete blocks [available for rent around here] for sides with plastic pond liner on outside and sheet pile on end, all placed with a crane. Total crane rental was 6hrs, portal to portal, actual placement took roughly 2 hrs. This job was simaler to yours, looking at the sandbag method I figure I saved $960, would have been around $1500 if sheet piling that was originally promised would have been available. Savings do not include cost of getting the sandbags to the jobsite.

    Have built dozens of sandbag coffer dams in live streams, most built by hand and the manhours they require for placement and removal just kill me. Whenever I can reach them with an excavator I use a combination of concrete blocks or steel sheets and sandbags, saves money and time.
    Understandibly your job specifications, labor and equipment costs could be very different from mine. Like you, I get lots of ideas from asking around, hope this helps.
     
    Last edited: Jul 9, 2011
  10. roddyo

    roddyo Senior Member

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    Can you pour it on Dry Ground and push it in with a Dozer?

    I have pushed in 18' before with a narrow track John Deere 450H.
    It don't get much cheaper than that.
     
  11. mitch504

    mitch504 Senior Member

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    What about ton bags for sandbags? They are about 4'x4'x4', and can be placed w/ a hoe. Most fertilizer dealers have used ones you could buy or maybe rent.

    They are an outer bag made of woven poly, like a regular sandbag, and have a waterproof plastic liner.
     
  12. SE-Ia Cowman

    SE-Ia Cowman Well-Known Member

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    I was watching tv the other night and on the news they were covering the flooding in western iowa they showed 1 ton sand bags that had 4 lifting straps in the corners and they were placeing them with helecopters but it could be done on your site with a crane. The bags looked like the same nylon bags we used to get seed soybeans in they are 4'x4'x4' the ones they had may have only been 2' tall
    I just did the math 4x4x4 is 3.5 ton of sand. I am shure the bags were smaller than our been bags but very much the same.

    Do you have sand avalible on the beach or do you have to truck it in?
     
  13. SE-Ia Cowman

    SE-Ia Cowman Well-Known Member

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    mitch we were thinking the same I was just 2 slow of a keyboard opperator lol
     
  14. mitch504

    mitch504 Senior Member

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    If you're slower than me.... that's pitiful.:D
     
  15. willie59

    willie59 Super Moderator

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    One ton sand bags, not a bad idea.
     
  16. Tinkerer

    Tinkerer Senior Member

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    When I built my boat ramp on a rather large river (700 feet to the opposite shore) I formed and poured concrete to the waters edge. Then I laid a sheet of heavy plastic on the newly poured ramp. Next I built a concrete form on the plastic sheet. I installed rebar, and on the high end I put in a 1 inch bar all the way across and had it protruding through the center of the 2x6 form about a foot. I used that extended bar to lift the well cured section of concrete and simply picked up the end of it with my backhoe and flipped it over into the water. There was a terrific splash because when it went over center lifting it I let loose of the lifting chain so me and the backhoe didn't end up in the water. I only need to go 10 feet out into the water. Just far enough to get all the distance I need for my boat trailer. I think that if a person used a hydro-crane you could go out quite a long distance into the water and set the precast extensions in place.
     
  17. Turbo21835

    Turbo21835 Senior Member

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  18. Orchard Ex

    Orchard Ex Super Moderator

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    All good ideas. The 1 ton bags aren't general seen around here. Not that I couldn't find some if needed. There are helicopters flying overhead all day though. :) Right now I'm thinking of precasting sections like stumpjumper said. We thought of precasting the whole section and pushing it with a dozer but space and access is a problem. I was also thinking of using the wall blocks (2x2x6) and 10 mil sheeting if I need to pump it and pour it dry.
    forestroad - it's funny, when you said "crabpots filled with sandbags" I thought of our style crabpots here in the Chesapeake. They are about a 2' cube of chicken wire. It took me a minute to realize that you meant the big pots as seen on "Deadliest Catch" LOL.
    If anyone has more ideas please keep 'em coming.
     
  19. digger242j

    digger242j Administrator

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  20. grandpa

    grandpa Senior Member

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