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

1. PL
`$= (11.53 - 10.49)/(10.49 - 4.5) * 100$`

= 17.36 %

2. Liquid limit at 25 number of blows,

`$LL = ((26-25)* 49.8 + (25 - 2.17) * 47.5)/(26-17)$`

`$= 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
`$= 0.73 * [47.75 - 20]$`

`$=20.25 $` %

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