Laboratory methods for Determination of Consistency limits

 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.  

IT = IP/ IF