Question
Classify the following inorganic soil (provide both group symbol and group name) according to the Unified soil Classification System.
Percent passing no. 4 sieve = 100
Percent passing no. 200 sieve = 70
Liquid Limit (LL) = 49
Plastic Limit (PL) = 24
Explanation / Answer
No. 4 sieve is 4.75 mm size sieve and no. 200 sieve is 0.075 mm sieve. Percent soil retained over 0.075 mm sieve = 100-70 = 30 < 50 => Fine grained soil Liquid limit = 49 (b/w 35 & 50) => Intermediate compressible soil Plasticity index, Ip = liquid limit(Wl) - plastic limit(Wp) = 49 - 24 = 25 Equation of A-line: Ip = 0.73* (Wl - 20) => Ip = 0.73* (49 - 20) = 21.17 < 25 SO, the given soil lies above A-line and thus the soil is Inorganic Clay soil. Symbol of the given soil is CI where, C stands for clay & I stands for intermediate compressible.