Tremie method is the most acceptable method of concreting under water.
In this method a tremie pipe is inserted in the water up to the point where concrete is going to be placed. Generally the diameter of a tremie pipe varies from 20 cm to 30 cm. Depending upon the depth of concreting under water we can add more tremie pipe by coupling it with one another.
Before inserting the tremie pipe into the water, the bottom end of the tremie pipe must be closed with a plug or thick polythene sheet or other suitable material.
After tremie pipe reaches at the desired depth, a funnel is fitted to the top end of the tremie pipe, to facilitate pouring of concrete.
Then concrete having a very high slump of about 150 mm to 200 mm is poured into the funnel, until the whole length of tremie pipe is filled up with concrete.
Then the tremie pipe is lifted up and given a slight jerk by a winch & pulley arrangement. Due to application of jerk and weight of the concrete inside the pipe, the bottom plug fall and the concrete gets discharged.
At this stage, make sure that the end of the tremie pipe remains inside the concrete, because this will prevent entering of water into the pipe from the bottom.
When all of the concrete inside the pipe gets discharged, the tremie pipe is again completely filled with concrete and the process is repeated. This process of filling and discharging of concreting is repeated, without any interruption, until the concrete level comes above the water table.
Pumping of water should not be allowed while concreting, because it may suck cement particles from the concrete.
No compaction is required for under water concreting, as concrete gets compacted by the hydrostatic pressure of water.