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A procedure for classifying soils and aggregate based on their sieve analysis, liquid limit, and plasticity index. instructions for using charts and figures to determine the soil group and subgroup, as well as the textural classification. The report includes references to AASHTO M145 and various Standard Deviations (SD), and is intended for use in highway construction.
Typology: Lecture notes
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(1) Subtract 30 from the liquid limit of the soil. If the P.I. is equal to or less than the L.L. minus 30, the subgroup is A-7-5.
If the P.I. is greater than the L.L. minus 30, the subgroup is A-7-6.
Examples:
L.L. = 43 P.I. = 11
L.L. 43 - 30 = 13
The P.I. of 11 is less than 13; therefore, the subgroup is A-7-5.
L.L. = 43 P.I. = 15
L.L. 43 - 30 = 13
The P.I. of 15 is more than 13; therefore, the subgroup is A-7-6.
(3) Example:
Soil type A- Percent passing the #200 = 65 Liquid limit = 32 Plasticity index = 13
The group index is 7.
Silty Soils
Clayey Soils
General Rating As Subgrade
Excellent to Good
Fair to Poor
Constituent Materials Usual Types of Significant
Stone Fragments, Gravel, & Sand
Sand Fine
Silty or Clayey Gravel & Sand
Group Index
Liquid Limit fraction passing #40 Characteristics of
Plasticity Index
#200 #40 #10 Percent Passing: Sieve Analysis
Group Classification
A-1-a
A-1-b
(With suggested subgroups)
General Classification
Granular Materials
(35% or less passing the #200)
Silt-Clay Materials
(More than 35% passing the #200)