Placing Concrete Under Water With Tremie Concrete
Class 4 - Session 3

When you're ready to place concrete, you cannot simply pull up to the side of the trench and discharge the concrete from the back of the truck into the trench. The concrete cannot be allowed to fall through the slurry or through the water.

If you pouring any kind of a structure below water. If the concrete fell through the water or the slurry, the fines would wash out of the heavy aggregate and you would not achieve a homogeneous result. You need to contain the concrete and segregate it from the surrounding water or slurry. We demonstrate how it's done for slurry walls, but the same method would apply any time you're placing concrete underwater.
provide a hopper and multiple lengths of tremie pipe

You begin with a hopper to create an easy target for the concrete and then you add length of tube, approximately 8 inches in diameter. They come in sections. They're assembled to any length you need and you lower this assembly down to the bottom of the excavation.

When you begin placing concrete, the weight of the concrete within the tube will push the concrete out of the bottom of the tube and displace the slurry instead of mixing with the slurry. The discharge end of the tube must always be submerged in concrete. After a period of time, you have to begin removing these sections of tremie pipe.

The concrete will begin to set and you need to get the tremie pipe out as you advance the work. You do some calculation to determine how far will one concrete truck go. Or two concrete trucks? And you determine at what point you want to begin lifting out the tube.

You continuously lift out sections of the tremie pipe, always keeping in mind when you reinstall the tremie pipe, the tip of the pipe has to be below the level of the concrete, so that you're always placing concrete into concrete and displacing the slurry.