Question

Sieve analysis on a dry soil sample of mass 1000g showed that 980g and 270g of soil pass through 4.75 mm and 0.075 mm sieve respectively. The liquid limit and plastic limit of the soil fraction passing through 425 $\mu$ sieves are 40% and 18%, respectively. The soil may be classified as

• A. SC
• B. MI
• C. CI
• D. SM

Answer 1

The correct option is A SC

Total mass of dry sample = 1000 g

Soil passing through 4.75 mm sieve

= 980 g

$=\frac{980}{1000}\times 100=98\%$

Soil passing through 0.075 mm sieve

= 270 g = 27%

Liquid limit, $w_L=40\%$

Plastic limit, $w_p=18\%$

Plasticity Index, $I_p=w_L-w_P$

= 40 - 18 = 22%

Since less than 50% passes through 0.075 mm sieve, soil is coarse grained

More than 50% of coarser fraction passes through 4.75 mm sieve, so it is sand.

Since fines(< .075 mm) are more than 12%
so using A line chart

$I_{PC}=0.73(w_L-20)$

= 0.73 (40 - 20) = 14.6

$I_p>I_{PC},$ So point lies above A line (clayey type)

Hence, soil is classified as SC