For determination of the permeability of a soil specimen by the variable head permeameter
Theory
The variable head permeameter is utilized to compute the permeability of comparatively less porous soils. The coefficient of permeability is expressed by:
Where,
= initial head,
= 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.
Tool and equipment
The tools and equipment essential for constant head Permeability test and following:
- Supporting frame for the stand pipe and the clamp
- Graduated glass stand pipe and the clamp
Process:
1. Expel the collar of the mould. Take the measurement of the inward measurements of the mould. Measure the mould with sham plate to the closest gram.
2. Apply a little oil within to the mould. Fasten the mould between the base plate and the expansion collar, and place the assembly on a strong base.
3. Take around 2.5kg of the soil specimen, from a completely blended wet soil, in the mould. Now compress the soil at the mandatory dry thickness utilizing a reasonable compacting equipment.
4. Expel the collar and base plate. Trim the unnecessary soil level with the highest point of the mould.
5. Clean the exterior of the mould and the of the dummy plate. Compute the weight of the dirt in the mould.
6. Take a little specimen of the soil in a compartment for the water content determination.
7. Immerse the permeable disc (stones).
8. Put a permeable disc on the drainage base and keep a channel paper on the permeable plate.
9. Evacuate the dummy plate and place the mould with soil on the drainage base subsequent to embedding a washer in the middle.
10. Clean the edges of the mould. Apply oil in the furrows around them.
11. Put a proper filter paper, a permeable disc and settle the drainage top utilizing washers.
12. Join the water reservoir to the outlet at the base, and permit the water to stream upwards, till it has immersed the specimen. Give the free water a chance to gather for a profundity of around 100mm on the highest point of the specimen.
[Alternatively the soil of low porousness can be soaked by exposing the example to a bit by bit expanding vacuum with base outlet shut in order to expel the air from the voids. Increment the vacuum step by step to 700mm of mercury and keep up it for at least 15minutes, contingent on the kind of the soil. Take after the evacuation by a procedure of moderate immersion of the specimen from the base upward under full vacuum. At the point when the example is immersed, close both the top and base outlets.]
13. Fill the unfilled segment of the mould with coveted water without aggravating the soil.
14. Separate the source from the outlet at the base.
15. Fix the stand pipe of compatible diameter to the inlet at the crest. Fill the stand pipe with water.
16. Unclutter the stop clock at the crest and permit the water to flow out through until the point where all the air in the mould is detached.
17. Shut the stop clock and permit the water from the stand pipe to flow from the soil sample.
18. Choose the heights, ![clip_image002[1]](https://civilarc.com/wp-content/uploads/2018/03/clip_image0021.gif){kind=small}
and ![clip_image003[1]](https://civilarc.com/wp-content/uploads/2018/03/clip_image0031.gif){kind=small}
compute beyond the midpoint of the outlet so that their difference is approximately 300 to 400mm. Note down the level parallel to a height 
.
19. Open up the valve and initiate the stop watch. Mark down the time gap for the head to fall from ![clip_image002[2]](https://civilarc.com/wp-content/uploads/2018/03/clip_image0022.gif){kind=small}
to ![clip_image004[1]](https://civilarc.com/wp-content/uploads/2018/03/clip_image0041.gif){kind=small}
and additionally also from ![clip_image004[2]](https://civilarc.com/wp-content/uploads/2018/03/clip_image0042.gif){kind=small}
to ![clip_image003[2]](https://civilarc.com/wp-content/uploads/2018/03/clip_image0032.gif){kind=small}
. These two time intervals shall be equivalent if the steady conditions have been started.
20. Carry on the steps (19) for minimum twice after altering the heights ![clip_image002[3]](https://civilarc.com/wp-content/uploads/2018/03/clip_image0023.gif){kind=small}
and ![clip_image003[3]](https://civilarc.com/wp-content/uploads/2018/03/clip_image0033.gif){kind=small}
.
21. Shut the flow of water. Detach all the parts.
22. Take a small amount of the soil sample for water proportion determination.
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 =
Length of sample=
Diameter of sample =
Volume of sample=
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  |
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| 4 | Final head  |
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| 5 | Head  |
|||
| 6 | Time interval | |||
 to  |
||||
 to  |
||||
 to  . |
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| Calculations | ||||
| 7 | Mass of soil = (2) – (1) | |||
| 8 | Bulk Density  |
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| 9 | Dry density  |
|||
| 10 | Void ratio  |
|||
| 11 |  |
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Result:
Coefficient of permeability of the given soil = ____mm/sec.