Question

The laboratory test results of a soil sample are given below

Percentage finer than 4.75 mm = 60

Percentage finer than 0.075 mm = 30

Liquid Limit = 35%; Plastic Limit = 27%

The soil classification is

• A. GM
• B. SM
• C. GC
• D. ML-MI

Answer 1

The correct option is A GM

Percentage finer than 4.75 mm = 60

Percentage finer than 0.075 mm = 30

Liquid limit, $W_L$ = 35%

Plastic Limit, $W_p$ = 27%

As fines ( < 0.075 mm) are less than 50% so soil is coarse grained (either gravel or sand)

As more than 50% of coarser fraction retained on 4.75 mm sieve $\Rightarrow$ gravel (G)

Fines are more than 12%, so using plasticity chart

$I_P=W_L-W_P$

= 35 - 27 = 8%

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

= 0.73 (35 - 20) = 10.95

$I_P<I_{PC}$ , point lies below A line, so it is silty in nature.

Hence soil is classified as GM