Tremie Concrete for Underwater Installation
Tremie Concrete for Underwater Installation
(OP)
Are there any good articles or texts on tremie concrete? I've looked at ACI 304 (pretty good)and Nawy's "Concrete Construction Handbook"(just OK) which both had some advice. It just seems like there are a lot of engineers who know of tremie installation, but very few who have any real experience.
The contractor says they know what they're doing, but I'm skeptical.
The contractor says they know what they're doing, but I'm skeptical.





RE: Tremie Concrete for Underwater Installation
http://www.dfi.org/viewpub.asp?tid=TM-CONCRETE2016
https://publications.csiro.au/rpr/download?pid=csi...
http://www.bittner-shen.com/publication/Drilled_Sh...
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RE: Tremie Concrete for Underwater Installation
RE: Tremie Concrete for Underwater Installation
Advances in concrete technology have allowed several techniques that make tremie placement less necessary. Better pump mixes, better/larger pumps, mix proportioning to better alleviate segregation from drop placement, better set and hydration control and other progress.
Further, tremie placement requires quite a bit of expensive, large equipment (crane, concrete bucket, etc)....plus it is relatively slow!
RE: Tremie Concrete for Underwater Installation
Edit: Also, what are the contractor's proposed means and methods?
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RE: Tremie Concrete for Underwater Installation
As far as means and methods, they want to use one 150 cu yd. per hour pumper and one spare. One tremie pipe, 5 inches in diameter. Site has limited access and is in a slightly remote location. There's a lot of things they want to do that contradict ACI 304 (five inch pipe, dragging the pipe across the pour, etc.).
I'd prefer multiple chutes pre-positioned in a 15 or 20 foot grid shuffled around while pouring continues. While one is being used, the others could be staged.
RE: Tremie Concrete for Underwater Installation
RE: Tremie Concrete for Underwater Installation
A thickness of 4.5 feet is "thin" for tremied concrete, especially since there is so much volume to be placed. As noted above (pipe embedded 2 ft.) a good bit of the total thickness may be minimally acceptable (especially at the perimeter) even under the best of conditions.
The surface of tremied concrete typically has a slope of about 1:6 (it can range from 1:3 to 1:12). The 15 ft. grid you mentioned is just right to minimize this issue. Dragging the pipe horizontally through the concrete is a no-no. If the concrete could be placed fast enough (not going to happen with one pumper) the pipes could be "leap frogged" around the area (instead of having 30, or so, pipes on a 15 ft. grid.
A few other items:
Concrete mix with high cement content: often 6.5 to 7 bags cement per cubic yard (some may "wash out" during underwater placement).
High slump concrete: typically 8 inches (needed since vibration is not practical).
A temporary plug in the 10 inch diameter (minimum) steel (not aluminum) pipe at the beginning of placement. This is to ensure the first concrete deposited has not segregated.
In the concrete mix, use gravel (rounded) instead of crushed stone. Less flow resistance.
Are there any specs on tremied concrete in the contract?
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RE: Tremie Concrete for Underwater Installation
The contractor is full of confidence, from their one installation, which I haven't seen. As I said, I'm worried about delivery, pumping, placing and everything else. And I know for certain that whatever crap they place, they won't take out, even if you could remove it with a spoon.
RE: Tremie Concrete for Underwater Installation
RE: Tremie Concrete for Underwater Installation
No reinforcing. Concrete is a cofferdam plug, but will be used to resist uplift and sliding for the completed structure.
RE: Tremie Concrete for Underwater Installation
IMHO, what this overconfident contractor is proposing guarantees that the seal will be little more than a thick layer of gravel, with little or no cement - certainly not anything that would pass for concrete. The concrete is exiting a 5" hose moving straight down, located just above the bottom. Velocity is over 8 ft/sec (based on 150 yd3/hr). I expect cement in the fresh mix will be washed out quickly.
The second purpose of a seal is to resist artesian water pressure after cofferdam dewatering. Gravel won't do that.
Third, depending on sheet pile embedment and cofferdam internal bracing, the seal resists high horizontal hydrostatic forces after dewatering. Not a job for gravel.
A depth of 30 ft. is a major cofferdam, in my book. Please read this link:
Design Loads and Construction of Tremie Sealed Cofferdams
I hope that I am misinterpreting the situation, but have been around cofferdams my entire life... they are dangerous. I'm aware of multiple fatalities since cofferdam failure is often both sudden and catastrophic.
www.SlideRuleEra.net
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RE: Tremie Concrete for Underwater Installation
What happened was someone used the attached chart without realizing it wasn't applicable in this situation.
RE: Tremie Concrete for Underwater Installation
I'm not worried about the plug if it gets installed correctly. SlideRuleEra, if you're right, and the concrete is truly horrible, the contractor will be reinstalling as necessary. I am worried that the result will be somewhere in between gravel and good concrete. Plus, it's one of those things that if the project goes south, nobody looks good, no matter how many times we raised a red flag.
RE: Tremie Concrete for Underwater Installation
Is it possible to have the contractor perform a small-scale test of his proposed method? IMHO, that would be money well spent. For everyone's benefit, need to do everything possible to prevent having to remove an incompetent cofferdam seal. Taking out 1400 yd3 of thick, porous, weak concrete is a big deal. Especially since the removal will have to be performed underwater (even with the exterior well points in full operations). The excavation could be dewatered, but to do this deep-well submersible pumps and big bucks will be needed.
This overconfident contractor reminds me of a favorite Mark Twain quotation:
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