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Soil Classification Procedure: Determining Soil and Aggregate Group and Subgroup, Lecture notes of Soil Mechanics and Foundations

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

2021/2022

Uploaded on 09/27/2022

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SD 103
mso.mat 9-16
Soil Classification
1. Scope:
This procedure is for classifying soils and aggregate.
2. Apparatus:
2.1 For sieve analysis see SD 202.
2.2 For mechanical analysis (Colloid) see SD 102.
2.3 Liquid limit and plasticity index see SD 207.
3. Procedure:
3.1 Field Classification.
A. Obtain the sieve analysis in accordance with SD 202 and the liquid
limit and plasticity index in accordance with SD 207.
B. With the required data from SD 202 and SD 207, determine the
classification from the chart, figure 1.
C. Enter the chart from the left and proceed to the right. The first group
which the test data fits is the correct group classification.
D. A-7 group only. To determine the subgroup of A-7 soil, use the
following:
(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.
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Soil Classification

1. Scope:

This procedure is for classifying soils and aggregate.

2. Apparatus:

2.1 For sieve analysis see SD 202.

2.2 For mechanical analysis (Colloid) see SD 102.

2.3 Liquid limit and plasticity index see SD 207.

3. Procedure:

3.1 Field Classification.

A. Obtain the sieve analysis in accordance with SD 202 and the liquid

limit and plasticity index in accordance with SD 207.

B. With the required data from SD 202 and SD 207, determine the

classification from the chart, figure 1.

C. Enter the chart from the left and proceed to the right. The first group

which the test data fits is the correct group classification.

D. A-7 group only. To determine the subgroup of A-7 soil, use the

following:

(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.

Page 2

E. Determination of Group Index.

(1) The following must be known to determine the group index:

The percent passing the #200 sieve, liquid limit and plasticity

index.

(2) The group index is the sum of the values determined from

figure 2. and figure 3.

(3) Example:

Soil type A- Percent passing the #200 = 65 Liquid limit = 32 Plasticity index = 13

(4) Enter figure 2. with 65 percent passing the #200 and a liquid

limit of 32.

Follow the line for 65 percent passing the #200 up to the line

marked L.L. 40 or less. This will give you a value of 6.

(5) Using figure 3, enter the chart on the line marked passing the

#200, 55 or more.

(6) Follow the line marked 55 to the point (By interpolation) for a

P.I. of 13. This will give a value of 1.

(7) Total the values obtained from figure 2. and figure 3.

The group index is 7.

3.2 Central Laboratory.

A. The sieve analysis may be taken from SD 102 or SD 202.

B. The procedure in the Central Laboratory is the same as shown in

paragraph 3.1.

C. The Central Laboratory will also determine the textural classification

from figure 4.

D. To use this chart, obtain the percent clay and percent silt from the

colloid test, SD 102.

E. Enter the chart with the known percent clay and percent silt, where the

lines cross is the textural classification.

Page 4

Silty Soils

Clayey Soils

General Rating As Subgrade

Excellent to Good

Fair to Poor

11+^ 0-

Constituent Materials Usual Types of Significant

Stone Fragments, Gravel, & Sand

Sand Fine

Silty or Clayey Gravel & Sand

Group Index

11+^ 0-

Liquid Limit fraction passing #40 Characteristics of

Plasticity Index

N.P.

0-10^ 51-

#200 #40 #10 Percent Passing: Sieve Analysis

A-

A-

A-

Group Classification

A-1-a

A-1-b

A-

A-2-

A-2-

A-2-

A-2-

A-

A-

A-

A-7-6A-7-

CLASSIFICATION OF HIGHWAY SUBGRADE MATERIALS

(With suggested subgroups)

General Classification

Granular Materials

(35% or less passing the #200)

Silt-Clay Materials

(More than 35% passing the #200)

Figure 1

Page 5

OR LESS PERCENT PASSING THE #200 OR MORE

Figure 3

OR MORE PERCENT PASSING THE #200 OR LESS

Figure 2