DHARM64 GEOTECHNICAL ENGINEERING454035302520LL = 31.5%Flow curve10 15 20 25 30 40
Number of blowsN(log scale)
Fig. 3.18 Flow graph
If = (w 2 – w 1 )/log 10 (N 1 /N 2 ) ...(Eq. 3.43)
If the flow curve is extended such that N 1 and N 2 correspond to one log-cycle difference,
If will be merely the difference of the corresponding water contents.
One-point Method
Attempts have been made to simplify the trial and error procedure of the determination
of liquid limit described above. One such is the ‘One-point method’ which aims at determining
the liquid limit with just one reading of the number of the blows and the corresponding mois-
ture content.
The trial moisture content should be as near the liquid limit as possible. This can be
done with a bit of experience with the concerned soils. For soils with liquid limit between 50
and 120%, the accepted range shall require 20 to 30 drops to close the groove. For soils with
liquid limit less than 50%, a range of 15 to 35 drops is acceptable. At least two consistent
consecutive closures shall be observed before taking the moisture content sample for calculation
of the liquid limit. The test shall always proceed from the drier to the water condition of the
soil. (IS: 2720, Part V-1970).
The water content wN of the soil of the accepted trial shall be calculated. The liquid limit
wL of the soil shall be calculated by the following relationship.
wL = wN(N/25)x ...(Eq. 3.44)where
N = number of drops required to close the groove at the moisture content wN. Prelimi-
nary work indicates that x = 0.092 for soils with liquid limit less than 50% and x = 0.120 for
soils with liquid limit more than 50%.
Note: The liquid limit should be reported to the nearest whole number. The history of the soil
sample, that is, natural state, air-dried, oven-dried, the method used, the period of soaking should also
be reported.
Cone Penetration Method
This method is based on the principle of static penetration. The apparatus is as ‘Cone
Penetrometer’, consisting of a metallic cone with half angle of 15° 30′ ± 15′ and 30.5 mm coned
depth (IS: 2720, Part V–1985). It shall be fixed at the end of a metallic rod with a disc at the top