CE161P-2
GEOTECHNICAL
ENGINEERING 1
MODULE 2
SCHOOL OF CIVIL, ENVIRONMENTAL, AND GEOLOGICAL ENGINEERING
SCHOOL OF CIVIL, ENVIRONMENTAL, AND GEOLOGICAL ENGINEERING
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
DETERMINATION OF PARTICLE SIZE OF SOILS

Soils generally are called gravel, sand, silt, or clay, depending on the
predominant size of particles within the soil.
©Google
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
DETERMINATION OF PARTICLE SIZE OF SOILS

Soils generally are called gravel, sand, silt, or clay, depending on the
predominant size of particles within the soil.

To describe soils by their particle size, various classification systems have evolved
over the years to describe soils based on their particle size distribution. Such as:
Massachusetts Institute of Technology (MIT)
U.S. Department of Agriculture (USDA)
Unified Soil Classification System (USCS),
the American Association of State Highway Transportation Official (AASHTO);
American Society for Testing and Materials (ASTM) – a modification of the USCS
system; and
o British Standards (BS)
o
o
o
o
o
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
DETERMINATION OF PARTICLE SIZE OF SOILS

Comparison of four systems for describing soils based on particle size.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
DETERMINATION OF PARTICLE SIZE OF SOILS

Comparison of four systems for describing soils based on particle size.
© Budhu, M. (2011)
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
DETERMINATION OF PARTICLE SIZE OF SOILS

Soil can be classified based on particle size into two primary categories: coarsegrained and fine-grained soils.

Mechanical analysis is the determination of the size range of particles present in
a soil. Two methods generally are used to find the particle-size distribution of soil:
1) sieve analysis—for particle sizes larger than 0.075 mm in diameter, and
2) hydrometer analysis—for particle sizes smaller than 0.075 mm in diameter.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
DETERMINATION OF PARTICLE SIZE OF SOILS

They are determined through sieve analysis (ASTM D6913; AS 1289.3.6.1) in
coarse-grained soils and through hydrometer analysis (ASTM D422; AS
1289.3.6.3) in fine-grained soils.

The relative proportions of the different grain sizes in a soil are quantified in the
form of grain size distribution, particularly for course-grained soil.
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SCHOOL OF CIVIL, ENVIRONMENTAL, AND GEOLOGICAL ENGINEERING
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PARTICLE SIZE OF COARSE-GRAINED SOILS

The determination of particle size distribution or mean grain
diameter for coarse-grained soils involves sieving a measured
soil weight through a series of sieves.

In sieve analysis, a coarse-grained soil is passed through a set
of sieves stacked, with smaller openings at the bottom and
progressively larger ones towards the top, through which the
coarse-grained soil is passed.
Sieve no. 4
Sieve no. 10
Sieve no. 100
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PARTICLE SIZE OF COARSE-GRAINED SOILS

The grain size distribution data is
generally presented in the form of a
grain size distribution curve.

Since the grain sizes vary in a wide
range, they are usually shown on a
logarithmic scale.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PARTICLE SIZE OF COARSE-GRAINED SOILS

In the grain size distribution curve, the
percentage passing is plotted against the
corresponding grain size.

The results are plotted on a graph of percent of
particles finer than a given sieve size (Note: not
the percent retained) as the ordinate versus the
logarithm of the particle sizes as shown in the
particle size distribution curve.

The percent finer (or % passing) is:
%𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇 𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕 𝒊𝒊𝐭𝐭𝐭𝐭 𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔 = 𝟏𝟏𝟏𝟏𝟏𝟏 − �
𝒊𝒊
(%𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓 𝒐𝒐𝒐𝒐 𝒊𝒊𝒊𝒊𝒊𝒊 𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔)
𝒊𝒊=𝟏𝟏
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PARTICLE SIZE OF COARSE-GRAINED SOILS
Sample Problem:
1. 900 g soil was sent through the sieves, and the masses
retained are shown in the figure in the right. What is the
percentage of soil finer than 0.425 mm.
%𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇 𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕 𝟑𝟑𝟑𝟑𝟑𝟑 𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔 (𝟎𝟎. 𝟒𝟒𝟒𝟒𝟒𝟒𝟒𝟒𝟒𝟒)
𝒊𝒊
= 𝟏𝟏𝟏𝟏𝟏𝟏 − �
(%𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓𝒓 𝒐𝒐𝒐𝒐 𝒊𝒊𝒊𝒊𝒊𝒊 𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔)
𝒊𝒊=𝟏𝟏
= 𝟏𝟏𝟏𝟏𝟏𝟏 − (𝟖𝟖. 𝟖𝟖𝟖𝟖 + 𝟐𝟐𝟐𝟐 + 𝟐𝟐𝟐𝟐. 𝟐𝟐𝟐𝟐)
= 𝟒𝟒𝟒𝟒. 𝟗𝟗𝟗
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PARTICLE SIZE OF COARSE-GRAINED SOILS
Sample Problem:
1. 900 g soil was sent through the sieves, and the masses
retained are shown in the figure in the right. What is the
percentage of soil finer than 0.425 mm.
(𝟐𝟐𝟐𝟐𝟐𝟐 + 𝟏𝟏𝟏𝟏𝟏𝟏 + 𝟔𝟔𝟔𝟔)
𝒙𝒙 𝟏𝟏𝟏𝟏𝟏𝟏𝟏
%𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇 𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕 𝟑𝟑𝟑𝟑𝟑𝟑 𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔 𝟎𝟎. 𝟒𝟒𝟒𝟒𝟒𝟒𝟒𝟒𝟒𝟒 =
𝟗𝟗𝟗𝟗𝟗𝟗
Interpretation:
= 𝟒𝟒𝟒𝟒. 𝟗𝟗%
“That 48.9% of the soil is finer than 0.425mm.” OR
“That 48.9% of the soil passes thru 0.425mm (Sieve No. 40)”
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SCHOOL OF CIVIL, ENVIRONMENTAL, AND GEOLOGICAL ENGINEERING
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
GRAIN SIZE DISTRIBUTION

A coarse-grained soil is said to be well-graded if it consists of soil grains
representing a wide range of sizes where the smaller grains fill the voids created
by the larger grains, thus producing a dense packing.

A coarse-grained soil that cannot be described as well-graded is a poorly graded
soil.

Uniformly graded soils and gap-graded soils are two special cases of poorly
graded soils.

In uniformly graded soils, most of the grains are about the same size or vary within
a narrow range. Some references referred this type of soil as "poorly-graded."

In a gap-graded soil, there are no grains in a specific size range.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
GRAIN SIZE DISTRIBUTION
WELL-GRADED
POORLY-GRADED
GAP-GRADED
UNIFORMLY-GRADED
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
GRAIN SIZE DISTRIBUTION

The grain size distribution gives a complete and quantitative picture of the relative
proportions of the different grain sizes within the soil mass.

At this stage, let’s define some important grain sizes such as D10, D30, D50 and
D60, which are used to define the shape of the grain size distribution curve.

D10 is the grain size corresponding to 10% passing; i.e., 10% of the grains are
smaller than this size. Similar definitions hold for D30, D50, D60, etc.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
GRAIN SIZE DISTRIBUTION

The diameter D10 is called the effective size of the soil and was described by
Allen Hazen (1892) in connection with his work on soil filters.
The effective size is particularly important in regulating the flow of water through
soils, and can dictate the mechanical behavior of soils
The higher the D10 value, the coarser the soil and the better the drainage
characteristics.

D50 is the average grain size diameter of the soil.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
GRAIN SIZE DISTRIBUTION
Sample Problem:
1. [continuation] 900 g soil was sent through the sieves, and the masses
retained are shown in the figure in the right. What is the percentage of
soil finer than 0.425 mm.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
GRAIN SIZE DISTRIBUTION
Sample Problem:
1. 900 g soil was sent through the sieves, and the masses
retained are shown in the figure in the right. What is the
percentage of soil finer than 0.425 mm.
Solving for D10;
𝟏𝟏𝟏𝟏 − 𝟔𝟔. 𝟕𝟕
𝟐𝟐𝟐𝟐. 𝟐𝟐 − 𝟔𝟔. 𝟕𝟕
=
(𝒍𝒍𝒍𝒍𝒍𝒍 𝒙𝒙 − 𝒍𝒍𝒍𝒍𝒍𝒍 𝟎𝟎. 𝟎𝟎𝟎𝟎𝟎𝟎) 𝐥𝐥𝐥𝐥𝐥𝐥 𝟎𝟎. 𝟏𝟏𝟏𝟏 − 𝒍𝒍𝒍𝒍𝒍𝒍 𝟎𝟎. 𝟎𝟎𝟎𝟎𝟎𝟎

𝒙𝒙 = 𝟎𝟎. 𝟎𝟎𝟎𝟎 𝒎𝒎𝒎𝒎
Through interpolation, D10 = 0.09 mm, D30 = 0.20 mm, and D60 = 1.42 mm.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
GRAIN SIZE DISTRIBUTION

The shape of the grain size distribution curve is described through two simple
parameters: the coefficient of uniformity (Cu) and the coefficient of curvature
(Cc)**.
𝒊𝒊
𝐷𝐷60
𝑪𝑪𝒖𝒖 =
𝐷𝐷10
𝒊𝒊𝒊𝒊
𝐷𝐷30 2
𝑪𝑪𝒄𝒄 =
𝐷𝐷10 𝐷𝐷60
**Other references uses other terms for Cc such as coefficient of gradation and the coefficient of concavity.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
GRAIN SIZE DISTRIBUTION


The Coefficient of uniformity, Cu value
ranges from 1 to higher values,
representing particle size diversity.
Uniform graded
A Cu < 4
signifies uniform-sized
particles, while values Cu > 4 indicate a
broader range of particle sizes.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
GRAIN SIZE DISTRIBUTION


Coefficient of curvature, Cc, ranges from
1 to 3 for well-graded soils.
Uniform graded
A Cc outside this range, along with a
sharp slope change in the particle size
distribution curve indicates gap-graded
soils with missing grain sizes.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
GRAIN SIZE DISTRIBUTION
Summary

Uniform Graded (or poorly-graded) soils
have uniformity coefficients, Cu < 4 and
steep gradation curves.

Well-graded soils have uniformity
coefficients, Cu > 4, and coefficients of
curvature, Cc between 1 and 3, and flat
gradation curves.

Gap-graded soils have coefficients of
curvature, Cc < 1 or > 3, and one or
more humps on the gradation curves.
Uniform graded
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
GRAIN SHAPE

Shapes of the grains can be angular, subangular, subrounded, or rounded.

When the grains are angular there is more interlocking among the grains, and
therefore the strength and stiffness of the soils would be greater. For example, in
roadwork, angular aggregates would provide better interlocking and resistance
against dislodgement.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
3. A sample of a dry, coarse-grained material of mass 500 grams was shaken through
a nest of sieves, and the following results were obtained:
Sieve no.
Opening (mm)
Mass Retained (g)
4
4.75
0
10
2.00
14.8
20
0.85
98
40
0.425
90.1
100
0.15
181.9
200
0.075
108.8
Pan
6.1
a. Plot the particle size distribution (gradation) curve.
b. Determine (1) the effective size, (2) the average particle size, (3) the uniformity
coefficient, and (4) the coefficient of curvature.
c. Describe the textural composition of the soil using the USCS classification.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
3.a. Plot the particle size distribution (gradation) curve.
Sieve no.
Opening (mm)
Mass Retained (g)
% Finer
4
4.75
0
100
10
2.00
14.8
97.04
20
0.85
98
77.43
40
0.425
90.1
59.40
100
0.15
181.9
22.99
200
0.075
108.8
1.22
Pan
6.1
499.7**
**The reduction in mass is due to losses mainly from a small quantity of soil
that gets stuck in the meshes of the sieves. You should use the “after
sieving” total mass of 499.7 grams in the calculations.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
3.b. Determine (1) the effective size, (2) the average
particle size, (3) the uniformity coefficient, and (4)
the coefficient of curvature.
(1) Effective size, D10
Based on the graph, D10 = 0.1 mm
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
3.b. Determine (1) the effective size, (2) the average
particle size, (3) the uniformity coefficient, and (4)
the coefficient of curvature.
(1) Effective size, D10
𝟏𝟏𝟏𝟏 − 𝟏𝟏. 𝟐𝟐𝟐𝟐
𝟐𝟐𝟐𝟐. 𝟗𝟗𝟗𝟗 − 𝟏𝟏. 𝟐𝟐𝟐𝟐
=
(𝒍𝒍𝒍𝒍𝒍𝒍 𝒙𝒙 − 𝒍𝒍𝒍𝒍𝒍𝒍 𝟎𝟎. 𝟎𝟎𝟎𝟎𝟎𝟎) 𝐥𝐥𝐥𝐥𝐥𝐥 𝟎𝟎. 𝟏𝟏𝟏𝟏 − 𝒍𝒍𝒍𝒍𝒍𝒍 𝟎𝟎. 𝟎𝟎𝟎𝟎𝟎𝟎
Sieve no.
Opening (mm)
Mass Retained (g)
% Finer
4
4.75
0
100
10
2.00
14.8
97.04
20
0.85
98
77.43
40
0.425
90.1
59.40
100
0.15
181.9
22.99
200
0.075
108.8
1.22
Pan
6.1
𝒙𝒙 = 𝑫𝑫𝟏𝟏𝟏𝟏 = 𝟎𝟎. 𝟏𝟏 𝒎𝒎𝒎𝒎
31
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
3.b. Determine (1) the effective size, (2) the average
particle size, (3) the uniformity coefficient, and (4)
the coefficient of curvature.
(2) Average particle size, D50
𝟓𝟓𝟓𝟓 − 𝟐𝟐𝟐𝟐. 𝟗𝟗𝟗𝟗
𝟓𝟓𝟓𝟓. 𝟒𝟒𝟒𝟒 − 𝟐𝟐𝟐𝟐. 𝟗𝟗𝟗𝟗
=
(𝒍𝒍𝒍𝒍𝒍𝒍 𝒙𝒙 − 𝒍𝒍𝒍𝒍𝒍𝒍 𝟎𝟎. 𝟏𝟏𝟏𝟏) 𝐥𝐥𝐥𝐥𝐥𝐥 𝟎𝟎. 𝟒𝟒𝟒𝟒𝟒𝟒 − 𝒍𝒍𝒍𝒍𝒍𝒍 𝟎𝟎. 𝟏𝟏𝟏𝟏
Sieve no.
Opening (mm)
Mass Retained (g)
% Finer
4
4.75
0
100
10
2.00
14.8
97.04
20
0.85
98
77.43
40
0.425
90.1
59.40
100
0.15
181.9
22.99
200
0.075
108.8
1.22
Pan
6.1
𝒙𝒙 = 𝑫𝑫𝟓𝟓𝟓𝟓 = 𝟎𝟎. 𝟑𝟑𝟑𝟑 𝒎𝒎𝒎𝒎
32
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
3.b. Determine (1) the effective size, (2) the average
particle size, (3) the uniformity coefficient, and (4)
the coefficient of curvature.
(3) the uniformity coefficient, Cu
𝑫𝑫𝟔𝟔𝟔𝟔
𝑪𝑪𝒖𝒖 =
𝑫𝑫𝟏𝟏𝟏𝟏
Sieve no.
Opening (mm)
Mass Retained (g)
% Finer
4
4.75
0
100
10
2.00
14.8
97.04
20
0.85
98
77.43
40
0.425
90.1
59.40
100
0.15
181.9
22.99
200
0.075
108.8
1.22
Pan
6.1
Solving for 𝐷𝐷60 ;
𝟔𝟔𝟔𝟔 − 𝟓𝟓𝟓𝟓. 𝟒𝟒𝟒𝟒
𝟕𝟕𝟕𝟕. 𝟒𝟒𝟒𝟒 − 𝟓𝟓𝟓𝟓. 𝟒𝟒𝟒𝟒
=
(𝒍𝒍𝒍𝒍𝒍𝒍 𝒙𝒙 − 𝒍𝒍𝒍𝒍𝒍𝒍 𝟎𝟎. 𝟒𝟒𝟒𝟒𝟒𝟒) 𝐥𝐥𝐥𝐥𝐥𝐥 𝟎𝟎. 𝟖𝟖𝟖𝟖 − 𝒍𝒍𝒍𝒍𝒍𝒍 𝟎𝟎. 𝟒𝟒𝟒𝟒𝟒𝟒
𝒙𝒙 = 𝑫𝑫𝟔𝟔𝟔𝟔 = 𝟎𝟎. 𝟒𝟒𝟒𝟒 𝒎𝒎𝒎𝒎
33
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
3.b. Determine (1) the effective size, (2) the average
particle size, (3) the uniformity coefficient, and (4)
the coefficient of curvature.
(3) the uniformity coefficient, Cu
𝑫𝑫𝟔𝟔𝟔𝟔
𝑪𝑪𝒖𝒖 =
𝑫𝑫𝟏𝟏𝟏𝟏
Sieve no.
Opening (mm)
Mass Retained (g)
% Finer
4
4.75
0
100
10
2.00
14.8
97.04
20
0.85
98
77.43
40
0.425
90.1
59.40
100
0.15
181.9
22.99
200
0.075
108.8
1.22
Pan
6.1
𝟎𝟎. 𝟒𝟒𝟒𝟒
𝑪𝑪𝒖𝒖 =
= 𝟒𝟒. 𝟑𝟑
𝟎𝟎. 𝟏𝟏
34
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
3.b. Determine (1) the effective size, (2) the average
particle size, (3) the uniformity coefficient, and (4)
the coefficient of curvature.
(3) the coefficient of curvature, Cc
𝑫𝑫𝟑𝟑𝟎𝟎 𝟐𝟐
𝑪𝑪𝒄𝒄 =
𝑫𝑫𝟏𝟏𝟏𝟏 𝑫𝑫𝟔𝟔𝟔𝟔
Sieve no.
Opening (mm)
Mass Retained (g)
% Finer
4
4.75
0
100
10
2.00
14.8
97.04
20
0.85
98
77.43
40
0.425
90.1
59.40
100
0.15
181.9
22.99
200
0.075
108.8
1.22
Pan
6.1
Solving for D30;
𝟑𝟑𝟎𝟎 − 𝟐𝟐𝟐𝟐. 𝟗𝟗𝟗𝟗
𝟓𝟓𝟓𝟓. 𝟒𝟒𝟒𝟒 − 𝟐𝟐𝟐𝟐. 𝟗𝟗𝟗𝟗
=
(𝒍𝒍𝒍𝒍𝒍𝒍 𝒙𝒙 − 𝒍𝒍𝒍𝒍𝒍𝒍 𝟎𝟎. 𝟏𝟏𝟓𝟓) 𝐥𝐥𝐥𝐥𝐥𝐥 𝟎𝟎. 𝟒𝟒𝟒𝟒𝟒𝟒 − 𝒍𝒍𝒍𝒍𝒍𝒍 𝟎𝟎. 𝟏𝟏𝟏𝟏
𝒙𝒙 = 𝑫𝑫𝟑𝟑𝟑𝟑 = 𝟎𝟎. 𝟏𝟏𝟏𝟏 𝒎𝒎𝒎𝒎
35
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
3.b. Determine (1) the effective size, (2) the average
particle size, (3) the uniformity coefficient, and (4)
the coefficient of curvature.
(3) the coefficient of curvature, Cc
𝑫𝑫𝟑𝟑𝟎𝟎 𝟐𝟐
𝑪𝑪𝒄𝒄 =
𝑫𝑫𝟏𝟏𝟏𝟏 𝑫𝑫𝟔𝟔𝟔𝟔
Sieve no.
Opening (mm)
Mass Retained (g)
% Finer
4
4.75
0
100
10
2.00
14.8
97.04
20
0.85
98
77.43
40
0.425
90.1
59.40
100
0.15
181.9
22.99
200
0.075
108.8
1.22
Pan
6.1
𝑫𝑫𝟑𝟑𝟎𝟎 𝟐𝟐
(𝟎𝟎. 𝟏𝟏𝟏𝟏)𝟐𝟐
= 𝟎𝟎. 𝟕𝟕𝟕𝟕
𝑪𝑪𝒄𝒄 =
=
𝑫𝑫𝟏𝟏𝟏𝟏 𝑫𝑫𝟔𝟔𝟔𝟔 (𝟎𝟎. 𝟏𝟏)(𝟎𝟎. 𝟒𝟒𝟒𝟒)
36
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
3.c. Describe the textural composition of the soil using the USCS classification (i.e., the amount
of gravel, sand, etc.).
Sieve no.
Opening (mm)
Mass Retained
(g)
% Finer
4
4.75
0
100
10
2.00
14.8
97.04
20
0.85
98
77.43
40
0.425
90.1
59.40
100
0.15
181.9
22.99
200
0.075
108.8
1.22
Pan
6.1
499.7
∴ 𝐭𝐭𝐭𝐭𝐭𝐭 𝐬𝐬𝐬𝐬𝐬𝐬𝐬𝐬 𝐢𝐢𝐢𝐢 𝐜𝐜𝐜𝐜𝐜𝐜𝐜𝐜𝐜𝐜𝐜𝐜𝐜𝐜𝐜𝐜 𝐨𝐨𝐨𝐨 𝐆𝐆𝐆𝐆𝐆𝐆𝐆𝐆𝐞𝐞𝐞𝐞 = 𝟎𝟎𝟎; 𝐒𝐒𝐒𝐒𝐒𝐒𝐒𝐒 = 𝟗𝟗𝟗𝟗. 𝟕𝟕𝟕𝟕%; 𝐚𝐚𝐚𝐚𝐚𝐚, 𝐒𝐒𝐒𝐒𝐒𝐒𝐒𝐒/𝐂𝐂𝐂𝐂𝐂𝐂𝐂𝐂 = 𝟏𝟏. 𝟐𝟐𝟐𝟐%
37
SCHOOL OF CIVIL, ENVIRONMENTAL, AND GEOLOGICAL ENGINEERING
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PARTICLE SIZE OF FINE-GRAINED SOILS

The common laboratory method used to determine the size
distribution of fine-grained soils is a hydrometer test.

The hydrometer test involves mixing a small amount of soil
into a suspension and observing how the suspension settles
in time. As the grains settle, the density of the suspension
decreases.

The time-density record is translated into grain
percentage passing data using Stokes’law.

The hydrometer data can be merged with those from sieve
analysis for the complete grain size distribution.
size
39
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PARTICLE SIZE OF FINED-GRAINED SOILS

Stoke’s Law
𝑫𝑫 =
where;
𝟏𝟏𝟏𝟏𝝁𝝁𝝁𝝁
(𝑮𝑮𝒔𝒔 − 𝟏𝟏)𝝆𝝆𝒘𝒘 𝒈𝒈𝒕𝒕𝑫𝑫
D = diameter (cm)
ρw = density of water (1 g/cm3)
tD = time (seconds)
g = acceleration due to gravity (981 cm/s2)
μ = viscosity of water (0.01 g/cm-s at 20OC)
Gs = specific gravity of soil particles
(For most soils, Gs = 2.7)
z = depth (cm)
40
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
2. At a certain stage in a hydrometer test, the vertical distance moved by soil particles
of a certain size over a period of 1 minute is 0.8 cm. The temperature measured is
20°C. If the specific gravity of the soil particles is 2.7, calculate the diameter of the
particles using Stokes’s law. Are these silt or clay particles?
𝑫𝑫 =
𝟏𝟏𝟏𝟏𝝁𝝁𝝁𝝁
=
(𝑮𝑮𝒔𝒔 − 𝟏𝟏)𝝆𝝆𝒘𝒘 𝒈𝒈𝒕𝒕𝑫𝑫
D = diameter (cm) = ?
𝟏𝟏𝟏𝟏 ∗ 𝟎𝟎. 𝟎𝟎𝟎𝟎 ∗ 𝟎𝟎. 𝟖𝟖
= 𝟎𝟎. 𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎 𝒄𝒄𝒄𝒄 = 𝟎𝟎. 𝟎𝟎𝟎𝟎𝟎𝟎 𝒎𝒎𝒎𝒎
𝟐𝟐. 𝟕𝟕 − 𝟏𝟏 ∗ 𝟏𝟏 ∗ 𝟗𝟗𝟗𝟗𝟗𝟗 ∗ 𝟔𝟔𝟔𝟔
ρw = density of water = 1 g/cm3 at 20OC
tD = time (seconds) = 1 minute = 60 seconds
g = acceleration due to gravity = 981 cm/s2
μ = viscosity of water = 0.01 gram/cm-s at 20OC
Gs = 2.7
z = depth (cm) = 0.8 cm
41
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
2. At a certain stage in a hydrometer test, the vertical distance moved by soil particles
of a certain size over a period of 1 minute is 0.8 cm. The temperature measured is
20°C. If the specific gravity of the soil particles is 2.7, calculate the diameter of the
particles using Stokes’s law. Are these silt or clay particles?
𝑫𝑫 = 𝟎𝟎. 𝟎𝟎𝟎𝟎𝟎𝟎 𝒎𝒎𝒎𝒎;
∴ 𝐭𝐭𝐭𝐭𝐭𝐭 𝐬𝐬𝐬𝐬𝐬𝐬𝐬𝐬 𝐩𝐩𝐩𝐩𝐩𝐩𝐩𝐩𝐩𝐩𝐩𝐩𝐩𝐩𝐩𝐩𝐩𝐩 𝐛𝐛𝐛𝐛𝐛𝐛𝐛𝐛𝐛𝐛𝐛𝐛 𝐭𝐭𝐭𝐭
𝐭𝐭𝐭𝐭𝐭𝐭 𝐬𝐬𝐬𝐬𝐬𝐬𝐬𝐬 𝐟𝐟𝐟𝐟𝐟𝐟𝐟𝐟𝐟𝐟𝐟𝐟𝐟𝐟𝐟𝐟 𝐨𝐨𝐨𝐨 𝐭𝐭𝐭𝐭𝐭𝐭 𝐬𝐬𝐬𝐬𝐬𝐬𝐬𝐬.
42
SCHOOL OF CIVIL, ENVIRONMENTAL, AND GEOLOGICAL ENGINEERING
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS

In 1911, Swedish scientist A. Atterberg developed
the Atterberg limits for pottery and were later
modified to suit geotechnical engineering needs by
Arthur Casagrande in 1932.

When a dry fine-grained soil is mixed with water in
small increments, the soil will pass through distinct
states known as solid, semi-solid, plastic solid
and liquid.
44
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS

Atterberg limits are simply borderline water
contents that separate the different consistencies
the fine-grained soils can have.

These borderline water contents are shrinkage
limit, plastic limit and liquid limit.
45
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS

Starting from point A down to point B, the soil flows
like a liquid.

At point B, the soil becomes so stiff that it can no
longer flow as a liquid. The boundary water content
at point B is called the Liquid Limit (LL).

As the soil continues to dry, there is a range of
water content at which the soil can be molded into
any desired shape without rupture - this state is
said to exhibit plastic behavior.
46
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS
Liquid Limit (LL)

The liquid limit is determined from an apparatus
that consists of a semispherical brass cup that is
repeatedly dropped onto a hard rubber base
from a height of 10 mm by a cam-operated
mechanism.
Arthur
Casagrande
(1932)
developed this apparatus, and the procedure for
the test is called the Casagrande cup method
(ASTM D 4318; AS 1289.3.1.1).
47
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS
Liquid Limit (LL)

Four or more tests at different water content
are usually required for terminal blows (number
of blows to close the groove over a distance of
12.5 mm) ranging from 10 to 40*.

The results are presented in a plot of water
content (ordinate, arithmetic scale) versus
terminal blows (abscissa, logarithmic scale).

The best-fit straight line to the data points,
usually called the flow line, is drawn
48
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS
Liquid Limit (LL)

The Liquid Limit is read from the graph as the
water content on the liquid state line
corresponding to 25 blows.
49
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
4. Results from liquid and plastic limit tests conducted on a soil are given below.
Liquid limit tests:
Number of Blows, N
Moisture Content (%)
14
38.4
16
36.5
20
33.1
28
27.0
Plastic limit tests: PL = 13.4%
Ans:
a. Determine the liquid limit.
(a) 29.05%
b. What is the plasticity index of the soil? (b) 15.65%
50
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS
Liquid Limit (LL)

Another method also in determining the liquid limit is through
the Swedish fall cone method (ASTM D4318; AS 1289.3.9.1).

The water content corresponding to a cone penetration of 20
mm defines the liquid limit.

Similar with the Casagrande cup method, four or more tests at
different water contents are also required because of the
difficulty of achieving the liquid limit from a single test.

Based on flow line, the liquid limit is read from the plot as the
water content on the liquid state line corresponding to a
penetration of 20 mm.
51
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS

As the soil continues to dry, there is a range of
water content at which the soil can be molded into
any desired shape without rupture - this state is
said to exhibit plastic behavior.

The water content at which the soil changes from a
plastic to a semisolid is known as the Plastic limit
(PL).
52
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS


The range of water contents over which the soil deforms plastically is known as
the Plasticity Index, PI.
𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷 𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰, 𝑷𝑷𝑷𝑷 = 𝑳𝑳𝑳𝑳 − 𝑷𝑷𝑷𝑷
Burmister (1949) classified the plasticity index in a qualitative manner as follows:
53
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS
Plastic Limit (LL)

The plastic limit is determined by rolling a small clay sample into threads and
finding the water content at which threads approximately 3mm in diameter will just
start to crumble (Plastic Limit Test – ASTM D 4318; AS 1289.3.2.1) .

Two or more determinations are made, and the average water content is
reported as the plastic limit.
54
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS

But, if drying is continued beyond the range of
water content for plastic behavior, the soil becomes
a semisolid. The soil cannot be molded now
without visible cracks appearing.

As the soil continues to dry, it comes to a final state
called the solid state. At this state, no further
volume change occurs since nearly all the water in
the soil has been removed.

The water content at which the soil changes from a
semisolid to a solid is called the Shrinkage Limit
(SL).
55
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS
Shrinkage Limit (SL)

The shrinkage limit is determined as follows. A mass of wet soil, M1, is placed in a
porcelain dish and then oven-dried. The volume of oven-dried soil is determined
by using mercury (ASTM D 427) to occupy the vacant spaces caused by
shrinkage.

The mass of the mercury is determined, and the volume decrease caused by
shrinkage can be calculated from the known density of mercury.
**Vi = V1; Vf = V2
56
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS
Shrinkage Limit (SL)

SL can be determined as difference between the initial moisture content when the
soil is placed in the shrinkage limit dish and the change in moisture content (that
is, between the initial moisture content and the moisture content at the shrinkage
limit).
𝑴𝑴𝟏𝟏 − 𝑴𝑴𝟐𝟐
𝑽𝑽𝟏𝟏 − 𝑽𝑽𝟐𝟐
𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳, 𝑺𝑺𝑺𝑺 =
−
𝝆𝝆𝒘𝒘 𝐱𝐱 𝟏𝟏𝟏𝟏𝟏𝟏
𝑴𝑴𝟐𝟐
𝑴𝑴𝟐𝟐
where M1 is the mass of the wet soil, M2 is the mass of the oven-dried soil, V1 is the volume of wet
soil, V2 (= mass of mercury/density of mercury) is the volume of the oven dried soil.
57
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS
Shrinkage Limit (SL)

Another parameter that can be determined from a shrinkage limit test is the
shrinkage ratio, which is the ratio of the volume change of soil as a percentage of
the dry volume to the corresponding change in moisture content.
∆𝑽𝑽
∆𝑽𝑽
𝑴𝑴𝟐𝟐
𝑽𝑽𝟐𝟐
𝑽𝑽𝟐𝟐
𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑹𝑹𝑹𝑹𝑹𝑹𝑹𝑹𝑹𝑹, 𝑺𝑺𝑺𝑺 =
=
=
∆𝑽𝑽𝝆𝝆𝒘𝒘
∆𝑴𝑴
𝑽𝑽𝟐𝟐 𝝆𝝆𝒘𝒘
𝑴𝑴𝟐𝟐
𝑴𝑴𝟐𝟐
58
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS
Shrinkage Limit (LL)

Linear shrinkage (LS) is a simple test to measure the potential of the clay to
shrink. The linear shrinkage ratio, LS, is:
𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺, 𝑳𝑳𝑳𝑳 = 𝟏𝟏 −
𝟑𝟑
𝑽𝑽𝟐𝟐
𝑽𝑽𝟏𝟏
59
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS
Shrinkage Limit (LL)

Through the shrinkage limit test, the specific gravity of soil solid could also be
determined through:
𝑮𝑮𝒔𝒔 =
𝟏𝟏
𝟏𝟏
𝑺𝑺𝑺𝑺
−
𝑺𝑺𝑺𝑺
𝟏𝟏𝟏𝟏𝟏𝟏
; 𝑺𝑺𝑺𝑺 𝒊𝒊𝒊𝒊 𝒊𝒊𝒊𝒊 (%)
60
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
5. Following are the results of a shrinkage limit test:
•
•
•
•
Initial volume of soil in a saturated state = 24.6 cm3
Final volume of soil in a dry state = 15.9 cm3
Initial mass in a saturated state = 44.0 g
Final mass in a dry state = 30.1 g
Determine the following
(a) 17.28%
a. Shrinkage Limit
(b) 1.89
b. Shrinkage Ratio; and
c. Specific Gravity of Soil Solids (c) 2.81
61
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS

At one extreme, the liquid state, the soil has the
lowest strength and the largest deformation. At the
other extreme, the solid state, the soil has the
largest strength and the lowest deformation.

A measure of soil strength using the Atterberg
limits is known as the liquidity index (LI) and is
expressed as:
𝒘𝒘 − 𝑷𝑷𝑷𝑷
𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳 𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰, 𝑳𝑳𝑳𝑳 =
𝑷𝑷𝑷𝑷
62
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS

Strength of Fine-Grained Soils Based on Liquidity Index
63
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS

Another index that is commonly used for
engineering purposes is the consistency index
(CI), which may be defined as:
𝑳𝑳𝑳𝑳 − 𝒘𝒘
𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪 𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰, 𝑪𝑪𝑪𝑪 =
𝑳𝑳𝑳𝑳 − 𝑷𝑷𝑷𝑷
64
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS

Let’s consider two different fine-grained soils X
(20% clay and 80% silts) and Y (80% clay and
20% silts), having the same plasticity index of 40.
In X, the 20% clay contributes to all the plasticity,
whereas in Y, there is a significantly larger quantity
of clay contributing to the same degree of plasticity.
Understandably, the clay component in X is more
plastic than the one in Y.
65
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
PHYSICAL STATES OF FINE-GRAINED SOILS

Skempton (1953) showed that for soils with a
particular mineralogy, the plasticity index is linearly
related to the amount of the clay fraction.

He coined a term called activity (A) to describe the
importance of the clay fractions on the plasticity
index.
𝑷𝑷𝑷𝑷
𝑨𝑨𝑨𝑨𝑨𝑨𝑨𝑨𝑨𝑨𝑨𝑨𝑨𝑨𝑨𝑨, 𝑨𝑨 =
𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪 𝑭𝑭𝑭𝑭𝑭𝑭𝑭𝑭𝑭𝑭𝑭𝑭𝑭𝑭𝑭𝑭 (%)
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Summary

Fine-grained soils can exist in one of four states: solid, semisolid, plastic, or liquid.

Water is the agent that is responsible for changing the states of soils.

The liquid (LL), plastic (PL), and shrinkage (SL) limits are, respectively, the
moisture contents (%) at which the consistency of soil changes from liquid to
plastic stage, plastic to semisolid stage, and semisolid to solid stage.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
6. A fine-grained soil has a liquid limit of 300% and a plastic limit of 55%. The natural
water content of the soil in the field is 80% and the clay content is 60%.
a. Determine the plasticity index, the liquidity index, and the activity.
b. What is the soil state in the field?
Ans:
(a) 245%, 0.1, and 4.1 respectively
(b) LI = 0.1 is at the low end of the plastic state.
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CE161P-2
GEOTECHNICAL
ENGINEERING 1
MODULE 2
PART II
SCHOOL OF CIVIL, ENVIRONMENTAL, AND GEOLOGICAL ENGINEERING
SCHOOL OF CIVIL, ENVIRONMENTAL, AND GEOLOGICAL ENGINEERING
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION

Different soils with similar properties may be classified into groups and subgroups
according to their engineering behavior.

Most of the soil classification systems that have been developed for engineering
purposes are based on simple index properties such as particle-size distribution
and plasticity.

Although several classification systems are now in use, none is totally definitive of
any soil for all possible applications because of the wide diversity of soil
properties.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION

In general, there are two major categories into which the classification systems
developed in the past can be grouped.
1.
2.
The textural classification is based on the particle-size distribution of the percent of
sand, silt, and clay-size fractions present in a given soil. In this chapter, we will
discuss the textural classification system developed by the U.S. Department of
Agriculture (USDA).
The other major category is based on the engineering behavior of soil and takes into
consideration the particle-size distribution and the plasticity (i.e., liquid limit
and plasticity index). Under this category, there are two major classification
systems in extensive use now:
a. The AASHTO classification system, and
b. The Unified classification system.
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SOIL CLASSIFICATION
TEXTURAL CLASSIFICATION - USDA

In a general sense, texture of soil refers to its surface appearance.

Soil texture is influenced by the size of the individual particles present in it. The
USDA Particle-Size Classifications divided soils into gravel, sand, silt, and clay
categories on the basis of particle size.

In most cases, natural soils are mixtures of particles from several size groups.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
TEXTURAL CLASSIFICATION - USDA

In the textural classification system, the
soils are named after their principal
components, such as sandy clay, silty
clay, and so forth.

The textural classification systems
developed by the U.S. Department of
Agriculture (USDA):
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
7.
Classify the following soils according to the USDA textural classification system.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
7. Classify the following soils according to the
USDA textural classification system.
SOIL C
∴ 𝑩𝑩𝑩𝑩𝑩𝑩𝑩𝑩𝑩𝑩 𝒐𝒐𝒐𝒐 𝑼𝑼𝑼𝑼𝑼𝑼𝑼𝑼 𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕 𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄
𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔, 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑪𝑪 𝒊𝒊𝒊𝒊 "𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
7. Classify the following soils according to the USDA
textural classification system.
 Note that this chart is based on only the fraction of soil
that passes through the No. 10 sieve (2mm).
 Hence, if the particle-size distribution of a soil is such that a
certain percentage of the soil particles is larger than 2 mm
in diameter, a correction will be necessary.
 Modified percentage(%):
𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺/𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪/𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 ∗ 𝟏𝟏𝟏𝟏𝟏𝟏
𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺/𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪/𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺(%) =
𝟏𝟏𝟏𝟏𝟏𝟏 − 𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
7. Classify the following soils according to the
USDA textural classification system.
SOIL D
SOIL C
SOIL B
SOIL A
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
7. Classify the following soils according to the
USDA textural classification system.
SOIL D
SOIL C
SOIL B
SOIL A
∴ 𝑩𝑩𝑩𝑩𝑩𝑩𝑩𝑩𝑩𝑩 𝒐𝒐𝒐𝒐 𝑼𝑼𝑼𝑼𝑼𝑼𝑼𝑼 𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕 𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄 𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔:
~ 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑨𝑨 𝒊𝒊𝒊𝒊 "𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪 𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺
~ 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑩𝑩 𝒊𝒊𝒊𝒊 "𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺
~ 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑫𝑫 𝒊𝒊𝒊𝒊 "𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
*CORRECTION
SOIL CLASSIFICATION
Sample Problem:
7. Classify the following soils according to the
USDA textural classification system.
SOIL D
SOIL C
SOIL B
SOIL A
∴ 𝑩𝑩𝑩𝑩𝑩𝑩𝑩𝑩𝑩𝑩 𝒐𝒐𝒐𝒐 𝑼𝑼𝑼𝑼𝑼𝑼𝑼𝑼 𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕 𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄 𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔:
~ 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑩𝑩 𝒊𝒊𝒊𝒊 " 𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮 𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺
Note:
• If the content of particles coarser than sand is 15 percent or more,
an appropriate modifier is added, for example, "gravelly.“
• E.g. If %Gravel is 15 or more, “gravelly” needs to be added.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
CLASSIFICATION BY ENGINEERING BEHAVIOR

Although the textural classification of soil is relatively simple, it is based entirely on
the particle-size distribution. The amount and type of clay minerals present in finegrained soils dictate to a great extent their physical properties.

Hence, plasticity must be consider, which results from the presence of clay
minerals, to interpret soil characteristics properly.

Currently, two more elaborate classification systems are commonly used by soils
engineers. Both systems take into consideration the particle-size distribution
and Atterberg limits.

They are the American Association of State Highway and Transportation
Officials (AASHTO) classification system and the Unified Soil Classification
System (USCS).
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
AASHTO Classification System

The AASHTO soil classification system is used to determine the suitability of soils
for earthworks, embankments, and road-bed materials.

According to AASHTO, granular soils are soils in which 35% or less are finer than
the No. 200 sieve (0.075 mm). Silt-clay soils are soils in which more than 35% are
finer than the No. 200 sieve.

Soil Types, Average Grain Size, and Description according to AASHTO
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
AASHTO Classification System

The AASHTO system classifies soils into seven major groups, A-1 through A-7.

The first three groups, A-1 through A-3, are granular (coarse-grained) soils,
while the last four groups, A-4 through A-7, are silt-clay (fine-grained) soils.
*B see the more detailed AASHTO Classification of Soils and Soil-Aggregate Mixtures for values
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
AASHTO Classification System

Detailed AASHTO Classification of Soils and Soil-Aggregate Mixtures
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
AASHTO Classification System

Detailed AASHTO Classification of Soils and Soil-Aggregate Mixtures
 for 𝐴𝐴 − 7 − 5, 𝑷𝑷𝑷𝑷 ≤ 𝑳𝑳𝑳𝑳 − 𝟑𝟑𝟑𝟑; 𝐴𝐴 − 7 − 6, 𝑷𝑷𝑷𝑷 > 𝑳𝑳𝑳𝑳 − 𝟑𝟑𝟑𝟑
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
AASHTO Classification System

This classification system is based on the following criteria
1. Grain Size
a. Gravel: fraction passing the 75-mm sieve and retained on the No. 10 (2-mm) sieve
b. Sand: fraction passing the No. 10 (2-mm) sieve and retained on the No. 200 (0.075-mm)
sieve
c. Silt and clay: fraction passing the No. 200 sieve
𝜇𝜇
𝜇𝜇
𝜇𝜇
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
AASHTO Classification System

This classification system is based on the following criteria
2. Plasticity: The term silty is applied when the fine fractions of the soil have a
plasticity index of 10 or less. The term clayey is applied when the fine fractions
have a plasticity index of 11 or more.
3. If cobbles and boulders (size larger than 75 mm) are encountered, they are
excluded from the portion of the soil sample from which classification is made.
However, the percentage of such material is recorded.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
AASHTO Classification System

To evaluate the quality of a soil as a highway subgrade material, one must also
incorporate a number called the group index (GI) with the groups and subgroups
of the soil.

This index is written in parentheses after the group or subgroup designation. The
group index is given by the equation:
𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮 𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰, 𝑮𝑮𝑮𝑮 = 𝑭𝑭𝟐𝟐𝟐𝟐𝟐𝟐 − 𝟑𝟑𝟑𝟑 𝟎𝟎. 𝟐𝟐 + 𝟎𝟎. 𝟎𝟎𝟎𝟎𝟎𝟎 𝑳𝑳𝑳𝑳 − 𝟒𝟒𝟒𝟒 + 𝟎𝟎. 𝟎𝟎𝟎𝟎(𝑭𝑭𝟐𝟐𝟐𝟐𝟐𝟐 − 𝟏𝟏𝟏𝟏)(𝑷𝑷𝑷𝑷 − 𝟏𝟏𝟏𝟏)
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
AASHTO Classification System

Following are some rules for determining the group index:
1. If it yields a negative value for GI (GI < 0), it is taken as 0.
2. The group index calculated is rounded off to the nearest whole number (for example,
GI = 3.4 is rounded off to 3; GI = 3.5 is rounded off to 4).
3. The group index of soils belonging to groups A-1-a, A-1-b, A-2-4, A-2-5, and A-3 is
always 0.
4. When calculating the group index for soils that belong to groups A-2-6 and A-2-7, use
the partial group index:
𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷 𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮𝑮 𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰, 𝑮𝑮𝑮𝑮 = 𝟎𝟎. 𝟎𝟎𝟎𝟎(𝑭𝑭𝟐𝟐𝟐𝟐𝟐𝟐 − 𝟏𝟏𝟏𝟏)(𝑷𝑷𝑷𝑷 − 𝟏𝟏𝟏𝟏)
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A and B in according to the AASHTO system. Which soil is better for a
subgrade?
*NP means “Nonplastic”
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
 According to AASHTO, granular soils are soils in which 35% or less are finer
than the No. 200 sieve (0.075 mm). Silt-clay soils are soils in which more than
35% are finer than the No. 200 sieve.
8. Classify Soils A and B in according to the AASHTO
system. Which soil is better for a subgrade?
STEP 1: Check the %passing (%finer) at sieve no. 200, to determine whether it’s
GRANULAR OR SILT-CLAY MATERIALS
SOIL B
SOIL A
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A and B in according to the AASHTO
system. Which soil is better for a subgrade?
STEP 2: Check the %passing (%finer) at sieve no. 10 to 200 and LL & PI , to
determine its GROUP CLASSIFICATION
Soil A
HOW TO USE THE TABLE:
 One must apply the test data from
LEFT TO RIGHT. By process of
elimination, the first group from the
left into which the test data fit is
the correct classification.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A and B in according to the AASHTO
system. Which soil is better for a subgrade?
STEP 2: Check the %passing (%finer) at sieve no. 10 to 200 and LL & PI , to
determine its GROUP CLASSIFICATION
Soil A
Solving for Group Index, GI:
𝑮𝑮𝑮𝑮 = 𝑭𝑭𝟐𝟐𝟐𝟐𝟐𝟐 − 𝟑𝟑𝟑𝟑 𝟎𝟎. 𝟐𝟐 + 𝟎𝟎. 𝟎𝟎𝟎𝟎𝟎𝟎 𝑳𝑳𝑳𝑳 − 𝟒𝟒𝟒𝟒
+𝟎𝟎. 𝟎𝟎𝟎𝟎(𝑭𝑭𝟐𝟐𝟐𝟐𝟐𝟐 − 𝟏𝟏𝟏𝟏)(𝑷𝑷𝑷𝑷 − 𝟏𝟏𝟏𝟏)
𝑮𝑮𝑮𝑮 = 𝟖𝟖𝟖𝟖 − 𝟑𝟑𝟑𝟑 𝟎𝟎. 𝟐𝟐 + 𝟎𝟎. 𝟎𝟎𝟎𝟎𝟎𝟎 𝟐𝟐𝟐𝟐 − 𝟒𝟒𝟒𝟒
+𝟎𝟎. 𝟎𝟎𝟎𝟎(𝟖𝟖𝟖𝟖𝟖𝟖𝟖𝟖)(𝟖𝟖 − 𝟏𝟏𝟏𝟏)
𝑮𝑮𝑮𝑮 = 𝟓𝟓. 𝟒𝟒 ≈ 𝟓𝟓
∴ 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑨𝑨 𝒊𝒊𝒊𝒊 𝑨𝑨 − 𝟒𝟒 (𝑮𝑮𝑮𝑮)
∴ 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑨𝑨 𝒊𝒊𝒊𝒊 𝑨𝑨 − 𝟒𝟒 (𝟓𝟓)
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A and B in according to the AASHTO
system. Which soil is better for a subgrade?
Soil B
∴ 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑩𝑩 𝒊𝒊𝒊𝒊 𝑨𝑨 − 𝟏𝟏 − 𝒃𝒃 (𝑮𝑮𝑮𝑮)
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A and B in according to the AASHTO
system. Which soil is better for a subgrade?
Soil B
Solving for Group Index, GI:
∴ 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑩𝑩 𝒊𝒊𝒊𝒊 𝑵𝑵𝑵𝑵𝑵𝑵 − 𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷;
𝑮𝑮𝑮𝑮 = 𝟎𝟎
∴ 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑩𝑩 𝒊𝒊𝒊𝒊 𝑨𝑨 − 𝟏𝟏 − 𝒃𝒃 (𝑮𝑮𝑮𝑮)
∴ 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑩𝑩 𝒊𝒊𝒊𝒊 𝑨𝑨 − 𝟏𝟏 − 𝒃𝒃(𝟎𝟎)
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A and B in according to the AASHTO system. Which soil is better for a
subgrade?
𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑩𝑩 𝒊𝒊𝒊𝒊 𝑨𝑨 − 𝟏𝟏 − 𝒃𝒃 𝑮𝑮𝑮𝑮 → 𝑺𝑺𝑺𝑺𝑺𝑺𝑺𝑺 𝑨𝑨 𝒊𝒊𝒊𝒊 𝑨𝑨 − 𝟒𝟒 (𝟓𝟓)
∴ 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝐴𝐴 𝑖𝑖𝑖𝑖 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 𝑡𝑡𝑡𝑡 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝐵𝐵 𝑖𝑖𝑖𝑖 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 𝑡𝑡𝑡𝑡 𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚
𝑓𝑓𝑓𝑓𝑓𝑓 𝑎𝑎 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠. 𝑇𝑇𝑇𝑇𝑇𝑇𝑇, 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝐵𝐵 𝑖𝑖𝑖𝑖 𝑡𝑡𝑡𝑡𝑡 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚.
97
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
USCS Classification System

The original form of this system was proposed by Casagrande in 1942 for use in
the airfield construction works undertaken by the Army Corps of Engineers during
World War II. In cooperation with the U.S. Bureau of Reclamation, this system was
revised in 1952.
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
USCS Classification System

At present, it is used widely by engineers (ASTM Test Designation D-2487). This
system classifies soils into two broad categories:
1. Coarse-grained soils that are gravelly and sandy in nature with less than 50%
passing through the No. 200 sieve. The group symbols start with a prefix of G or S.
o G stands for gravel or gravelly soil; and
o S for sand or sandy soil.
2. Fine-grained soils are with 50% or more passing through the No. 200
sieve. The group symbols start with prefixes of:
o
o
o
o
M stands for inorganic silt,
C for inorganic clay, or
O for organic silts and clays
The symbol Pt is used for peat, muck, and other highly organic soils
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
USCS Classification System

Other symbols used for the classification are:
o W—well graded
o P—poorly graded
o L—low plasticity (liquid limit less than 50)
o H—high plasticity (liquid limit more than 50)
100
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
USCS Classification System

Unified Soil Classification System (Based on Material Passing 76.2-mm Sieve)
101
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
USCS Classification System

Notes for Unified Soil Classification System
o
o
o
o
(a) Gravels with 5 to 12% fine require dual symbols: GW-GM, GW-GC, GP-GM, GP-GC.
(b) Sands with 5 to 12% fines require dual symbols: SW-SM, SW-SC, SP-SM, SP-SC.
(d) If 4 ≤ 𝑃𝑃𝑃𝑃 ≤ 7 and plots in the hatched area in the Plasticity Chart, use dual symbol GC-GM or SCSM.
(e) If 4 ≤ 𝑃𝑃𝑃𝑃 ≤ 7 and plots in the hatched area in the Plasticity Chart, use dual symbol CL-ML.
Plasticity Chart
*figure 5.3
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A according to the USCS system.
Sieve No.
Opening (mm)
%Finer A
4
4.75
90
8
2.36
64
10
2.00
58
20
0.85
35
40
0.425
22
80
0.18
15
100
0.15
10
200
0.075
4
No. 40 Fraction Characteristics
Liquid Limit, LL
46
Plastic Limit, PL
29
103
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A according to the USCS system.
STEP 1: Check the %passing / %finer
(or % retained, if given) at sieve no.
200, to determine whether it’s
COARSE-GRAINED SOIL OR FINEGRAINED SOIL
Sieve No.
Opening
(mm)
%Finer A
4
4.75
90
8
2.36
64
10
2.00
58
20
0.85
35
40
0.425
22
80
0.18
15
100
0.15
10
200
0.075
4
No. 40 Fraction Characteristics
Things to Note:
• %fine-grained = %passing through the
No. 200 sieve
• %course-grained = course fraction =
100 - %passing through the No. 200
sieve
Liquid Limit, LL
46
Plastic Limit, PL
29
or “Less than 50% passes
No. 200 sieve.”
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SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A according to the USCS system.
STEP 2: If Coarse-grained soil, determine whether Gravel or Sand and its type (for Finegrained soil; Silt and Clay – Inorganic/Organic)
Sieve No.
Opening
(mm)
%Finer A
4
4.75
90
8
2.36
64
10
2.00
58
20
0.85
35
40
0.425
22
80
0.18
15
100
0.15
10
200
0.075
4
No. 40 Fraction Characteristics
or “Less than 50% of coarse fraction
passes on No. 4 sieve.”
Liquid Limit, LL
46
Plastic Limit, PL
29
Things to Note:
• To check, compare the
%gravel
with
%sand,
and
determine which is greater.
• For Silts & Clays, it’s initially
assumed to be: “INORGANIC”
105
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
USCS Classification System

Notes for Unified Soil Classification System
o (a) Gravels with 5 to 12% fine require
dual symbols: GW-GM, GW-GC, GPGM, GP-GC.
o
(b) Sands with 5 to 12% fines require
dual symbols: SW-SM, SW-SC, SPSM, SP-SC.
o
(d) If 4 ≤ 𝑃𝑃𝑃𝑃 ≤ 7 and plots in the
hatched area in the Plasticity Chart,
use dual symbol GC-GM or SC-SM.
o
(e) If 4 ≤ 𝑃𝑃𝑃𝑃 ≤ 7 and plots in the
hatched area in the Plasticity Chart,
use dual symbol CL-ML.
Plasticity Chart
*figure 5.3
106
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A according to the USCS system.
STEP 3: Determine the GROUP SYMBOL, based on the parameters given.
Sieve No.
Opening
(mm)
%Finer A
4
4.75
90
8
2.36
64
10
2.00
58
20
0.85
35
40
0.425
22
80
0.18
15
100
0.15
10
200
0.075
4
No. 40 Fraction Characteristics
Liquid Limit, LL
46
Plastic Limit, PL
29
∴ 𝑇𝑇𝑇𝑇𝑇 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 𝑡𝑡𝑡𝑡 𝑡𝑡𝑡𝑡𝑡 𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 "𝑺𝑺𝑺𝑺𝑺
107
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A according to the USCS system.
STEP 4: Lastly, determine the “GROUP NAME”
108
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A according to the USCS system.
STEP 4: Lastly, determine the “GROUP NAME”
Sieve No.
Opening
(mm)
%Finer A
4
4.75
90
8
2.36
64
10
2.00
58
20
0.85
35
40
0.425
22
80
0.18
15
100
0.15
10
200
0.075
4
No. 40 Fraction Characteristics
Liquid Limit, LL
46
Plastic Limit, PL
29
∴ 𝑇𝑇𝑇𝑇𝑇 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑖𝑖𝑖𝑖 𝑎𝑎 "𝑾𝑾𝑾𝑾𝑾𝑾𝑾𝑾 − 𝒈𝒈𝒈𝒈𝒈𝒈𝒈𝒈𝒈𝒈𝒈𝒈 𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔
109
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A according to the USCS system.
 Other Table for Group Name
110
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A according to the USCS system.
 Other Table for Group Name
111
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A according to the USCS system.
 Other Table for Group Name (*referred to other table as figure 5.6)
112
SCHOOL OF CIVIL, ENVIRONMENTAL, GEOLOGICAL ENGINEERING
SOIL CLASSIFICATION
Sample Problem:
8. Classify Soils A according to the USCS system.
 Other Table for Group Name (*referred to other table as figure 5.6)
113
CE161P-2
GEOTECHNICAL
ENGINEERING 1
SCHOOL OF CIVIL, ENVIRONMENTAL, AND GEOLOGICAL ENGINEERING