VARIABLE HEAD PERMEABILITY TEST OF SOIL



TO DETERMINE THE PERMEABILITY OF A SOIL SPECIMEN BY THE VARIABLE HEAD PERMEAMETER

Theory:

The variable head permeameter is used to measure the permeability of relatively less pervious soils. The coefficient of permeability is given by

clip_image001

Where clip_image002= initial head, clip_image003= final head, t= time interval, a= cross-sectional area of the liquid stand pipe, A=cross-sectional area of the specimen, L= length of specimen.

Equipment:

All equipment required for constant head Permeability test and the following:

1. Graduated glass stand pipe and the clamp

2. Supporting frame for the stand pipe and the clamp

Procedure:

Steps 1 to 14 same as Constant head permeability test.

15. Connect the stand pipe of suitable diameter to the inlet at the top. Fill the stand pipe with water.

16. Open the stop cock at the top and allow the water to flow out till all the air in the mould is removed.

17. Close the stop cock and allow the water from the stand pipe to flow through the soil specimen.

18. Select the heights, clip_image002[1] and clip_image003[1] measured above the centre of the outlet such that their difference is about 300 to 400mm. mark the level corresponding to a height clip_image004.

19. Open the valve and start the stop watch. Record the time interval for the head to fall from clip_image002[2] to clip_image004[1] and also from clip_image004[2] to clip_image003[2]. These two time intervals will be equal if the steady conditions have established.

20. Repeat the steps (19) atleast twice after changing the heights clip_image002[3] and clip_image003[3].

21. Stop the flow of water. Disconnect all the parts.

22. Take a small quantity of the soil specimen for water content determination

Variable Head Permeability Test

Fig: Variable Head Permeability Test

DATA SHEET FOR VARIABLE HEAD PERMEAMETER TEST

Length of specimen=

Diameter of specimen =

Volume of specimen =

Water content =

Diameter of stand pipe =

Area of stand pipe =

Specific gravity of solids =

 

Sl. No.

Observations and Calculations

Determination No.

1

2

3

Observation

1

Mass of empty mould with base plate

 

 

 

2

Mass of mould, soil and base plate

 

 

 

3

Initial head clip_image001

 

 

 

4

Final head clip_image002

 

 

 

5

Head clip_image003

 

 

 

6

Time interval

 

 

 

clip_image001 to clip_image003

 

 

 

clip_image003 to clip_image002

 

 

 

clip_image001 to clip_image002.

 

 

 

Calculations

7

Mass of soil = (2) – (1)

 

 

 

8

Bulk Density clip_image004

 

 

 

9

Dry density clip_image005

 

 

 

10

Void ratio clip_image006

 

 

 

11

clip_image007

 

 

 

 

Result:

Coefficient of permeability of the given soil = ____mm/sec.