Question

A sample of blue gray soilwas obtained from Paine Field in Everett, WA to determine its Atterberg Limits and classify itssoil type according to the Unified Soil Classification system.84% of the sample passed through the #200 sieve with 16% retained on the #4 sieve. For one of the PL determinations, the wet weight + dish = 11.53 grams and the dry weight + dish = 10.49 grams. The dish only weighed 4.15 grams. Compute the plastic limit. Three determinations of the liquid limit were made. For 17 blows, the water content was 49.8%; for 26 blows, the water content was 47.5%; and for 36 blows, the water content was 46.3%.

Required:
Evaluate the soil type, indicate the information on a plasticity chart,and give the Unified Soil Classification System (USCS) symboland the proper narrative description.

Answer 1

Solution :

1. PL $= \frac{11.53 - 10.49}{10.49 - 4.5} \times 100$

       = 17.36 %

2. Liquid limit at 25 number of blows,

  $LL = \frac{(26-25)\times 49.8 + (25 - 2.17) \times 47.5}{26-17}$

       $= 47.75$ %

Since 84 % of the passes the number 200 sieve the soil is immediately fine grained and MI, OI or CI because LL = 47.75 % > 35%

Therefore, the Plasticity index, PI  $=47.75 - 17.36 = 30.39$ %

Equation of A-line $= 0.73 \times [47.75 - 20]$

                             $=20.25$ %

Thus the soil lies above the A-line, that is soil is medium compressible clay ---- CI