THEORY
As the soil loses moisture, either in its natural environment, or by
artificial means in laboratory it changes from liquid state to plastic state, from plastic state to
semi-solid state and then to solid state. Volume changes also occur with changes in water content. But there is particular limit at which any moisture change does not
cause soil any volume change.
Soils which undergo large volume changes with change in water content may
be troublesome. Volume changes may not and usually will not be equal. A shrinkage limit test should be performed on a soil.
1. To obtain a quantitative indication of how much change in moisture can occur before any appreciable volume changes occurs
2. To obtain an indication of change in volume. The shrinkage limit is useful in areas where soils undergo large volume changes
when going through wet and dry cycles (as in case of earth dams)
APPARATUS
1. Evaporating Dish. Porcelain, about 12cm diameter with flat bottom.
2. Spatula
3. Shrinkage Dish. Circular, porcelain or non-corroding metal dish (3 nos)
having a flat bottom and 45 mm in diameter and 15 mm in height internally.
4. Straight Edge. Steel, 15 cmm in length.
5. Glass cup. 50 to 55 mm in diameter and 25 mm in
height , the top rim of which is ground smooth and level.
6. Glass plates. Two, each 75 75 mm one plate shall be of plain glass and the
other shall have prongs.
7. Sieves. 2mm and 425- micron IS sieves.
8. Oven-thermostatically controlled.
9. Graduate-Glass, having a capacity of 25 ml and graduated to 0.2 ml and 100
cc one mark flask.
10.Balance-Sensitive to 0.01 g minimum.
11.Mercury. Clean, sufficient to fill the glass cup to over flowing.
12.Wash bottle containing distilled water.
PROCEDURE
Preparation of soil paste
1. Take about 100 gm of soil sample from a thoroughly mixed portion of the
material passing through 425-micron I.S. sieve.
2. Place about 30 gm the above soil sample in the evaporating dish and
thoroughly mixed with distilled water and make a creamy paste. Use water content some where around the liquid limit.
Filling the shrinkage dish
3. Coat the inside of the shrinkage dish with a thin layer of Vaseline to
prevent the soil sticking to the dish.
4. Fill the dish in three layers by placing approximately 1/3 rd of the amount
of wet soil with the help of spatula. Tap the dish gently on a firm base until the
soil flows over the edges and no apparent air bubbles exist. Repeat this process for 2nd
and 3rd layers also till the dish is completely filled with
the wet soil. Strike off the excess soil and make the top of the dish smooth. Wipe off all the soil adhering to the
outside of the dish.
5. Weigh immediately, the dish with wet soil and record the weight.
6. Air- dry the wet soil cake for 6 to 8hrs, until the colour of the pat turns
from dark to light. Then oven-dry the to constant weight at 1050C to 1100C say about 12 to
16 hrs.
7. Remove the dried disk of the soil from oven. Cool it in a desiccator. Then
obtain the weight of the dish with dry sample.
8. Determine the weight of the empty dish and record.
9. Determine the volume of shrinkage dish which is evidently equal to volume of
the wet soil as follows. Place the shrinkage dish in an evaporating dish and fill
the dish with mercury till it overflows slightly. Press it with plain glass plate firmly
on its top to remove excess mercury. Pour the mercury from the shrinkage dish into a
measuring jar and find the volume of the shrinkage dish directly. Record this volume as
the volume of the wet soil pat.
Volume of the Dry Soil Pat0
10. Determine the volume of dry soil pat by removing the pat from the
shrinkage dish and immersing it in the glass cup full of mercury in the following manner. Place the glass cup in a larger one and fill the glass cup to overflowing with
mercury.
11. Remove the excess mercury by covering the cup with glass plate with prongs and pressing it. See that no air bubbles are entrapped. Wipe out the outside of the
glass cup to remove the adhering mercury. Then, place it in another larger dish,
which is, clean and empty carefully.
12. Place the dry soil pat on the mercury. It floats submerge it with the pronged glass plate which is again made flush with top of the cup. The mercury spills over into the larger plate. Pour the mercury that is displayed by the soil pat into the measuring jar and find the volume of the soil pat directly.
OBSERVATION
|
S.No |
Determination No. |
1 |
2 |
3 |
|
1 |
Wt. of container in gm,W1 |
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2 |
Wt. of container + wet soil pat in gm,W2 |
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3 |
Wt. of container + dry soil pat in gm, W# |
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4 |
Wt. of oven dry soil pat, W0 in gm |
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5 |
Wt. of water in gm |
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6 |
Moisture content (%), W |
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7 |
Volume of wet soil pat (V), in cm |
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8 |
Volume of dry soil pat (V0) in cm3 |
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9 |
By mercury displacement method |
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10 |
a. Weight of displaced mercury |
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11 |
Shrinkage limit (WS)
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12 |
Shrinkage ratio (R) |
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RESULTS
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