ABSTRACT
The liquid limit is 56 percent, and the plasticity index 25 percent. Classify the soil according to the AASHTO classification system.
Solution
Percent of fine grained soil = 75
Computation of Group Index [Eq. (3.56a)]: a = 75 - 35 = 40 b = 75 - 15 = 60 c = 56 - 40 = 16, d = 25 - 10 = 15 Group Index, GI = 0.2 x 40 + 0.005 x 40 x 16 + 0.01 x 60 x 15 = 20.2
On the basis of percent of fine-grained soils, liquid limit and plasticity index values, the soil is either A-7-5 or A-7-6. Since (wl - 30)= 56 - 30 = 26 > Ip (25), the soil classification is A-7-5(20).
Example 3.21 Mechanical analysis on four different samples designated as A, B, C and D were carried out in a soil laboratory. The results of tests are given below. Hydrometer analysis was carried out on sample D. The soil is non-plastic.
