What is the purpose of keeping tremie pipe’s tip immersed in freshly-placed concrete for about 1m in underwater concreting?

  What is the purpose of keeping tremie pipe’s tip immersed in freshly-placed concrete for about 1m in underwater concreting? The size of tremie pipe is about 300mm with sections having flange couplings fitted with gasket to prevent water leakage. The tremie pipe should be closed initially to prevent water from entering the pipe. It should be designed with sufficient thickness and weight so that it would not be buoyant when empty inside water. The placement of tremie concrete is commenced by putting the closed pipe underwater to the location for concreting, followed by partial filling of tremie pipe with concrete. In order to have tremie concrete flowed out of the pipe, it is necessary to fill the pipe with concrete of sufficient height to overcome the water pressure and frictional head. After that the tremie pipe is raised about 150mm to allow concrete to flow out. To enhance sufficient bonding, each succeeding layer of concrete should be placed before the preceding layer has reached
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WHAT IS BULKAGE OF SAND???


BULKING OF SAND:

The Increase In The Volume Of  Dry Sand Due To Absorption Of Moisture Is Called

BULKING OF SAND, Bulking Of Sand Depends On The Quality Of Moisture In

The Sand And Also The Size Of The Particles. Five To Eight Percent Of The Increase

In The Moisture In The Sand Can Increase The Volume Of Sand Up To 20 To 40 Percent. 

TEST PROCEDURE TO DETERMINE BULKING OF SAND:

A)      Apparatus: 

 1)      20 lits, 25 litres measuring boxes (Farmas). 

 2)      Bucket.

 3)      Measuring tape        

 B)     Material     :      Sand  & Water

 C)    Procedure  :

 1)     Fill sand loosely in 20 litres, Measuring box and level with wooden log.

 2)     Unload the measured sand in 25 litres measuring boxes.

 3)     Fill 20-litre box with water up to ¾ heights.

 4)     Unload sand from 25 lit box in water in 20 lit box and level properly.

 5)     Remove water from top of sand and measure the level of sand at 4 places and take average depth.

 6)       Calculate Bulkage using the following formula.

 7)        Bulkage (%) = X x 100 / d

                        Where d = Final level of sand

                                    D = Initial level of sand

                                    X = Average depth of Settlement

   

  D)      Sample Calculations:

             Bulkage (%) = X x 100 / d

             Where d = Final level of sand

                        D = Initial level of sand

                        X = Average depth of Settlement

                        d  = D - X

                         X = Average depth of sand = X1 + X2 + X3 + X4 / 4

                         X1  = 4.5 cms.

                         X2  = 4.5 cms.

                         X3  = 4.5 cms.

                         X4 = 4.5 cms.

        Therefore,

                         X = ( 4.5 + 4.5 + 4 + 4) /4= 4.25 cms.

                         d = D – X = 30 - 4.25 = 25.75 cms

       Therefore,

                         % Bulkage = [4.25 / 25.75] x 100 = 16.5 %

 8)             Observation/Conclusion:   As Per Sample Calculation, Bulkage = 16.5%.

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