The principle of the Tremie method is to bring the concrete through a pipe to the interior of the concrete being poured, thus preventing contact with the surrounding water. Before concrete is poured into the tremie pipe, a plug that keeps the concrete separated from the water, is placed in the pipe. When the go-devil reaches the bottom, the pipe is .lifted, so that the concrete flows out. Concrete is continuously fed to the tremie pipe-through a hopper and the pipe is lifted as the concrete level rises. Concrete 1s added continuously until the pour is completed.

This is a method on how to place concrete underwater, this method place a big role in offshore concreting, since cement looses its strength and fade away under water, Tremie method is to be used. Tremie Concrete is done by using a formwork/pipe which will have one end of the formwork/pipe above water and other bottom end immersed under the water and with the help of gravity.

A tremie is a watertight pipe, generally 250mm in diameter, having a funnel shape hopper at its upper end and a loose plug at the bottom or discharge end. The valve at the discharge end is used to de-water the tremie and control the distribution of the concrete. The tremie is supported on a working platform above water level, and to facilitate the placing it is built up in 1 to 3.5m section.

During the concreting, air and water must be exclude from the tremie by keeping the pipe full of concrete all the time; and for this reason the capacity of the hopper should be at least equal to that of the tremie pipe. In charging the tremie a plug formed of paper is first inserted into the pipe as the hopper is filled the pressure of fresh concrete forces the plug down the pipe, and the water in the tremie I displaced by concrete.

More info and whorel article in OnePetro and EngineersToday. If you want learn more about it, check this article of Washington University.