University of Gondar
Institutes of Technology
Department of Civil Engineering
Soil Mechanics-I (CEng 2131)
By Genanaw M. (Msc)
E-mail: mengiegenanaw02@gmail.com
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Classification of Soils
References
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Das, B., M. (2014), “ Principles of geotechnical
Engineering ” Eighth Edition, CENGAGE Learning,
ISBN-13: 978-0-495-41130-7.
Knappett, J. A. and Craig R. F. (2012), “ Craig’s Soil
Mechanics” Eighth Edition, Spon Press, ISBN: 978- 0-
415-56125-9.
Introduction
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A soil classification system-
It is the arrangement of different soils with similar
properties into groups & subgroups based on their
application or to their probable engineering
behavior.
A classification for engineering purposes should be
based mainly on mechanical properties:
permeability, stiffness, strength.
Introduction
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The aim of a classification system is to establish a
set of conditions which will allow useful
comparisons to be made between different soils.
Most of the soils classification systems that have
been developed for engineering purposes are based
on simple index properties such as particle size
distribution & plasticity.
Soil Classification System
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Commonly based on grain size and soil
consistency. Several classification systems
exist:
1. Unified Soil Classification System (USCS)
(ASTM D2487-11).
2. American Association of State Highway and
Transportation Officials (AASHTO) (ASTM
D3282-09).
Unified Soil Classification System
(USCS)
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According to the USCS, the soils are divided into
two major categories:
1. Coarse-grained soil that are gravelly and sandy in
nature with less than 50 % passing through the
No 200 sieve ( that is F200 < 50%).
2. Fine-grained soils with 50% or more passing
through the No. 200 sieve ( that is F 200 > 50%).
Unified Soil Classification System
(USCS)
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The soil is classified into 15 groups:
Each group is designated a symbol consisting of
two capital letters.
The first letter is based on main soil type.
The second letter is based on gradation and
plasticity .
Unified Soil Classification System
(USCS)
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Unified Soil Classification System
10
(USCS)
Unified Soil Classification System
(USCS)
11
Unified Soil Classification System
12
(USCS)
Unified Soil Classification System
(USCS)
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F 200 = percent passing No. 200 sieve ( % of fines )
R4 = percent retained above No.4 sieve ( % of
Gravel )
R200 = percent retained above No.200 sieve.
F4 = percent passing No. 4 sieve
Unified Soil Classification System (USCS)
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Unified Soil Classification System (USCS)
15
Unified Soil Classification System
(USCS)
16
Unified Soil Classification System
(USCS)
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Unified Soil Classification System (USCS)
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Unified Soil Classification System (USCS)
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Plasticity Chart
Note:
If the results of your soil tests fall above the U – line
on the plasticity chart, you should be suspicious of
your results and repeat your tests.
Unified Soil Classification System
(USCS)
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Unified Soil Classification System
(USCS)
21
Unified Soil Classification System
(USCS)
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Unified Soil Classification System
(USCS)
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AASHTO Classification System
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The 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 ( 2mm ) sieve
b. Sand: fraction passing the No. 10 sieve and retained
on the No. 200 U.S. sieve.
c. Silt and clay: fraction passing No.200sieve.
AASHTO Classification System
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2. Plasticity : the term silty is applied when the fine
frictions of the soil have a plasticity index of 10 or
less. The term clayey is applied when the fine
frictions have a plasticity index of 11or more.
3. If cobbles and boulders are encountered, they are
excluded form the portion of the soil sample which
classification is made.
AASHTO Classification System
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According to the present form of this system,
soils can be classified according to eight major
groups, A-1 through A-8, based on their grain
size distribution, liquid limit, and plasticity
indices.
AASHTO Classification System
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Soils listed in groups A-1, A-2, and A-3 are coarse-
grained materials, and those in groups A-4, A-5,
A-6, and A-7 are fine-grained materials.
Peat, muck, and other highly organic soils are
classified under A-8. They are identified by visual
inspection.
AASHTO Classification System
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AASHTO Classification System
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AASHTO Classification System
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AASHTO Classification System
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AASHTO Classification System
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AASHTO Classification System
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AASHTO Classification System
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AASHTO Classification System
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Worked Examples
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Solution
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Worked Examples
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Worked Examples
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Thank You!!!!!!
