Laboratory Determination of Consistency limits
1). Plastic limit
1). 8g to 30g own dried soil is considered
2). some water is added in soil to make soil paste
3). this paste is converted form soil ball to cylindrical thread.
4). If at the crumbling of thread
i. diameter > 3 mm Add some water
ii. Diameter = 3mm Water content in soil = plastic limit of soil.
iii. diameter < 3mm Remove some water by kneading action
2). Liquid Limit
Soviet liquid Device method
Or
Cone penetration method
Indian standard (I.S) ASTM
Stainless steel cone Stainless steel cone
Central angle = 31° 30°
Sliding mass = 80g Sliding mass = 75g
5 sec --->20mm Penetration 5 sec ---> 1cm
Density index or relative Density
Cohesion less Soil
ID =( emax – e /emax - emin )×100
emax = void ratio of soil in loosest state = 0.91
emin = void ratio of soil in densest-slate = 0.35
e = void ratio if soil ( natural state )
Density index term is used only for cohesion less soils
ii. Density index of soil represent relative compactness (%compaction)
ID = 0 emax = e soil is in loosest state
ID = 100% emin = e Soil is in deepest state
Overall value 0≤ID≤100 Theoretical value
For sand particles Id = 94% Practical value
Id=
CASARGRANDE’S METHOD
i. A/c To this method liquid limit is the water content at which soil groove come in contact with reach other in 25 revolutions.
ii. This liquid limit is calculated on the basis of flow curve.
iii. This slope of flow curve is known as flow index.
IP = - (W2-W1) / log10N2-log10N1
IF = W1-W2 / log10 (N2/N1)
Flow index Represents the rate of loss of shear strength with increase in water content.
Toughness Index
i. The ratio of plasticity index to flow index is known as toughness index
ii. Toughness Index represents the gain of shear strength with decrease in water content of soil.
