Topic 3

TOPIC 3
BASIC CHARACTERISTICS OF SOIL

Prepared by: Julia Mohamed Uyob

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Upon completion this chapter, students should be
able to:
PLO 1 – Apply knowledge of applied mathematics,
applied science, engineering fundamental and an
engineering specialization as specified in DK1 to
DK4 respectively to wide practical procedures and
practices.
PLO 2 – Identify and analyze well-defined
engineering problems reaching substantiated
conclusions using method of analyze specific to
their field or activity (DK1 to DK4)

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Components Of Soils
➢ Soil are consisting of solid soil

particles, water, and air (or gas).
➢ When the soil is partially saturated, its

void space will be filled up by water as
well as air, it will behave as a three
phase system.
➢ The soil behave as a two phase
system, when its void space is filled
with either water or air (solid and
water or solid and air).
➢ The representation of different phases
of soil with diagrams is called as phase
diagram.

Three-phase diagram (Partially
saturated soil)

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Two-phase diagram (Completely Two-phase diagram (Completely
saturated soil) dry soil)

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Three Phase diagram
➢ From figure,
VT = Va + Vw + Vs

MT = Ma + Mw + Ms (but Ma=0), so
MT = Mw + Ms

Three-phase diagram (Partially
saturated soil)

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Basic Formula: Basic Formula:

Water content, Specific Gravity,
w = (Mw ÷ Ms) x 100 Gs = [Ms ÷(Vs ρw)]

Bulk density, Void ratio,
ρb = (MT ÷ VT) ……. g/cm3 or kg/m3 (1cm3 = 1ml)
e = Vv ÷ Vs

Dry density, Porosity,

ρd = (Ms ÷ VT) ….. kg/m3 n = Vv ÷ VT

Submerged density, ρsub = ρ’ Degree of Saturation,
ρ’ = ρsat – ρw ….. kg/m3 Sr = (Vw ÷ Vv) x 100

Bulk unit weight, If soil is fully saturated, voids are completely
γb = (ρb x g) ÷ 1000 ……. N/m3 or kN/m3 filled with water. There is no air. (Vw = Vv).

Sr = 0

Dry unit weight, Air Content,
γd = (ρd x g) ÷ 1000 ….. kN/m3

Ar = Va ÷ Vv

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Relationship among unit weight, void ratio, moisture content and specific gravity

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Example 1
The results of moisture content test are
Determination of Index Properties of as follows:
Soil Mass of empty can = 13.39g
➢ Those properties of soil which are Mass of wet soil sample + can = 64.37g
Mass of dry soil + can = 52.18g
used in the identification and Calculate the moisture content.
classification of soil are known as
Index Properties.

Solution:

Moisture content, w

= = −


= 64.37−52.18
52.18−13.39

= 0.314 = 31.4%

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Example 2
A soil sample has a volume 0.0183m3 and
mass 30.6kg. After dried in an oven, the
mass of soil become 27.2kg. Given the
specific of gravity is 2.65. Calculate:

a. Bulk density (1672.13 kg/m3)
b. Dry density (1486.34 kg/m3)
c. Moisture content (12.5%)
d. Void ratio (0.777)
e. Porosity (43.7%)
f. Degree of saturation (42.5%)
g. Air content (25.1%)

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Example 3

A sample of gray silty clay has a mass of
126kg. Laboratory tests results give a bulk
density of 2.05 g/cm3, a specific gravity of
solids of 2.71, and a moisture content of
15.7%. Determine the:
a) Void ratio (0.530)
b) Porosity (34.6%)
c) Degree of saturation (80.3%)
d) Dry density (1772.1 kg/m3)
e) Dry unit weight (17.38 kN/m3)
f) Bulk unit weight (20.11 kN/m3)

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Example 4

A sample of moist soil was found to have the
following characteristics:

Total volume: 0.01456 m3
Total mass: 25.74 kg
Mass after oven drying: 22.10 kg
Specific gravity of solids: 2.69

Determine:
(a) Bulk density (1768 kg/m3)
(b) Bulk unit weight (17.34 kN/m3)
(c) Moisture content (16.5%)
(d) Void ratio (0.772)
(e) Porosity (43.5%)
(f) Degree of saturation (57.4%)

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Sieve Analysis

Grain Size Analysis • The test is carried out with the utilization of a
set of sieves with different mesh sizes.
• Grain size analysis is a typical laboratory test
conducted in the soil mechanics field. The • Each sieve has squared shaped openings of a
purpose of the analysis is to derive the certain size.
particle size distribution of soils.
• The sieve separates larger from smaller
• Sieve Grain Size Analysis is capable of particles, distributing the soil sample in 2
determining the particles’ size ranging from quantities (retained and passing)
0.075 mm to 100 mm.
• Therefore, the soil particles are distributed as
• particles smaller than 0.075 mm can be they are retained by the different sieves.
distributed using the Hydrometer Method.
• A pan is also used to collect those particles
that pass through the last sieve (No. 200).

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Sieve Analysis

Sieve Analysis Based on the range of the particle sizes,
and the Unified Soil Classification
The sieves typically used for Grain Size System (USCS), soils can be classified in
Analysis of soils as well as the the generic categories presented
corresponding opening sizes are in Table 2 below.
presented in Table 1 below.
Soil type Particle Size (mm)
Sieve (#) Opening Diameter (mm) Clay <0.002
4 4.75 Silt
10 2 Fine 0.002-0.075
20 0.85 0.075-0.42
40 0.425 Sand Medium
60 0.25 Coarse 0.42-2
2-4.75
100 0.15 Gravel 4.75-75
140 0.105
200 0.075

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Sieve Analysis
YouTube link:
Sieve Analysis

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Sieve Analysis

Sieve Analysis ➢ The values of the uniformity coefficient
Cu and the coefficient of gradation Cc can be
➢ The grain-size distribution of the calculated using the following equations:
soil sample can be obtained by
plotting the percent finer with the ➢ The values of Cu and Cc are used to classify
corresponding sieve on semi-log whether the soil is well-graded or not.
graph paper.
Sand is considered • Cu is greater than 6
➢ The values of D10, D30, and D60, well-graded if: • Cc is between 1 and 3
which are the diameters that
correspond to the percent finer of Gravel is considered • Cu is greater than 4
10%, 30%, and 60%, respectively well-graded if: • Cc is between 1 and 3
can be determined from the grain-
size distribution curve.

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Sieve Analysis- Particle Size Distribution
Curve

➢ Also known as gradation curve

➢ It represents the distribution of particles
of different sizes in the soil

➢ It is a graph of the results obtained from
sieve analysis, on a semi-log paper

➢ Figure 3.6 shows particle size distribution
curve. Curves on the left side of the
graph, such as soil A, indicate fine grained
soils, while those on the right of the
curve, such as soil B, indicate coarse
grained soils.

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Sieve Analysis- Gradation of soil • A soil sample is said to be well graded if it
has all sizes of materials present in it.
➢ Gradation describes the
Well Graded

distribution of different sizes of

individual particles within a soil

sample. The particle size • Poorly graded soil is a soil sample in which
most of the particles are approximately of
distribution curve is used to define Poorly the same size.
Graded
the grading of soil.

➢ A soil sample may be either:

• Well graded • A soil sample is said to be gap graded if at
least one particle size is completely missing
• Poorly Graded in it. Gap graded soils are sometimes
considered a type of poorly graded soil.
• Gap Graded Gap Graded

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Sieve Analysis- Gradation of soil

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Example 6

Example 5 Following are the results of a sieve analysis. Draw a particle-
size distribution curve and determine the value Cu and Cc and
Following are the results of a sieve analysis and the results are grade of the soil samples.
shown in table 2.3 below. Determine the value of Cu and Cc
and grade of the soil samples. Sieve size (mm) Mass retained (g)
37.5 0
Sieve size (mm) Mass retained (g) 20.0 59
5.0 11 10.0 38
2.36 18 5.0 33
1.18 24 2.36 27
0.6 21 1.18 30
0.3 41 0.6 22
32 0.3 15
0.212 16 0.212 17
0.15 22 0.15 16
0.063 20 0.063 9
Pan Pan 11

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

YouTube link:

Hydrometer Test https://www.youtube.com/watch?v=gtl
GoCq7OSk
➢ The particle size distribution of soil containing
a significant number of finer particles (silt and
clay) cannot be performed by sieve analysis.

➢ Hydrometer method is used to determine the
particle size distribution of fine-grained soils
passing 75 µ sieve and if more than 10% of the
soil passes the No.200 sieve.

➢ The hydrometer measures the specific gravity
of the soil suspension at the center of its bulb.

➢ The specific gravity depends upon the mass of
solids present, which in turn depends upon
the particle size.

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Atterberg Limit

Atterberg Limit The water content at which the soil
changes from one state to the other
➢ In 1911, Albert Atterberg define the limits known as consistency limits or
of soil consistency for the classification of Atterberg’s limit
fine-grained soils. He found that plasticity
is a unique property of cohesive (clay and
silt) soils and suggested classifying soils
with a particle size of 2µm (0.002mm) or
less as clays.

➢ Atterberg limits tests establish the
moisture contents at which fine-grained
clay and silt soils transition between
solid, semi-solid, plastic, and liquid states.

➢ Each stage exhibits significant differences
in strength, consistency, and behavior.

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Atterberg Limit State

Liquid State Liquid Limit (LL) Plastic State Plastic Limit (PL)

• A soil containing high • Which soil changes from • At some water content • Water content at
water content is in liquid liquid state to plastic soil becomes plastic from which soil changes
state state liquid state when water from plastic to
content is reduced semi-solid state
• It offers no shearing • Liquid Limit is the water
resistance content at which soil • Soil in plastic state can be • Water content at
ceases to be liquid molded into various shape which soil just fails
• Can flow like liquid to behave
• No resistance to shear • It is determined by • A water content is plastically
➢Casagrande’s apparatus reduced, the plasticity of
deformation or soil decreases
➢Cone penetration
method

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Atterberg Limit State

Plasticity Index (PI) Semi Solid State Shrinkage Limit (SL) Solid State

• It is the difference • When water content is • The water content at which soil • A stage is reached
between liquid reduced below plastic changes from semi-solid state when further
limit and plastic limit, soil attains a to solid state reduction in water
limit semi-solid state content doesn’t
• SL = e/Gs causes change in
• PI = LL - PL • The soil in this state volume of soil
cracks when moulded • SL is the water content at
which soil stops shrinking • The soil is then said
• The volume of soil further and attains a constant to have reached
decreases with the volume solid state from
decrease in water semi-solid state
content • SL is the lowest water content
at which soil is fully saturated

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Atterberg Soil Indexes

Plasticity Index, Plasticity Index (PI) = LL – PL
PI Soil with a high PI have a higher clay content or very high plasticity

Liquidity index, Liquidity Index (LI) = (PL – Natural Water Content) ÷ PI
LI Soil with LI > 1 or more will be closer to the liquid state
Soil with 0 < LI < 1 the soil behave like a plastic
Soil with LI < 0 or lower indicates soils that are harder and more brittle

Consistency Consistency Index (CI) = (LL – Natural Water Content) ÷ PI
Index, CI As CI increases, the shear strength of soil also increases

Activity Activity Number (A) = PI ÷ Clay-Size fraction (particles finer than 2µm)
number (A) Soil with A < 0.75 considered inactive clay
Soil with 0.75 <A < 1.25 considered normal clay
Soil with A > 1.25 considered active and will have an increased volume
change in response to moisture content.

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Casagrande method

Liquid Limit Test
➢ Liquid Limit can be determined using:

Casagrande Method
Cone Penetrometer Method

Casagrande Method
➢ In the Casagrande cup method, the

soil paste is placed in the Casagrande
cup, and a groove is made at the
center of it.
➢ at least three tests for the same soil
are conducted at varying moisture
contents, with the number of blows,
N, varying between 15 and 35.

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Cone Penetrometer method
✓ It consists of a stainless steel cone

which has its apex angle of 30°.
✓ This cone has a length of 35 mm.
✓ It is attached to the base of a steel

plunger rod. Weight of this assembly
is 80 gm.
✓ This arrangement can slide vertically
on pressing a push button. And it all
fixed to a stand with a base by a
clamping screw.

✓ Enough amount of soil is placed in the
brass cup of 50 mm internal diameter and
50 mm height. We need to ensure that no
air is entrapped in the cup. Surface of the
soil is levelled, and the cup is placed
below the cone.

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Plastic Limit Test

Plastic Limit test

➢ The Plastic limit test is performed by
repeated rolling of an ellipsoidal-sized soil
mass by hand on a non-porous surface.

➢ The soil samples must be crumbles when
it is carefully rolled out to a diameter of 3
mm

➢ If the thread crumbles at diameter
smaller than 3 mm, the soil is too wet.

➢ If the thread crumbles at a diameter
greater than 3 mm, the soil is drier than
the plastic limit.

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Plasticity Chart

Plasticity Chart ➢ To classify as soil based on the
plasticity chart, plot the PI and LL of
➢ Plasticity Chart, developed by Arthur the soil on the chart; the region in
Casagrande (1932) is a plot of the Plasticity which the point falls indicates the
Index (PI) versus the Liquid Limit (LL) of soils. type of fine-grained soil it is.

➢ The chart is used for the classification of fine
grained soils (or fine grained fraction of coarse
grained soils) based on their plasticity.

➢ A-line is an empirically chosen line which
separates the chart between clays and silts;
soils that fall above A-line are classified as clays
and that falling below as silts.

➢ There is also a vertical line in the plasticity
chart which corresponds to a liquid limit of
50% and separates the high plasticity fine
grained soils (LL>50%) from low plasticity fine
grained soils (LL<50).

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Soil Classification Systems

Soil Classification Systems Primary Letters Secondary Letters
✓ Further improved systems allowed G : Gravel W : Well Graded
S : Sand P : Poorly Graded
for the plasticity characteristics of M : Silt M : Silty (non-plastic fines)
soil and a modified form of the C : Clay C : Clayey (plastic fines)
system proposed by Casagrande in O : Organic L : Low Plasticity
1947 is the basis of the soil Pt : Peat H : High Plasticity
classification system used in
Britain
✓ The system divides soil into two
main categories – coarse and fine.
✓ Each group is identified using a
group symbol. The group symbol
consists of primary and secondary
descriptive letters.

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Soil Classification Systems

Soil Classification Systems Primary Letters Secondary Letters
✓ Further improved systems allowed G : Gravel W : Well Graded
S : Sand P : Poorly Graded
for the plasticity characteristics of M : Silt M : Silty (non-plastic fines)
soil and a modified form of the C : Clay C : Clayey (plastic fines)
system proposed by Casagrande in O : Organic L : Low Plasticity
1947 is the basis of the soil Pt : Peat H : High Plasticity
classification system used in
Britain ✓ This system classifies the soil into 15 different
✓ The system divides soil into two groups.
main categories – coarse and fine.
✓ Each group is identified using a ✓ The major divisions, however, include three
group symbol. The group symbol categories namely :
consists of primary and secondary •
descriptive letters. Coarse-grained > 50% of →thGe, soil is
retained on a 0.075mm sieve S
• aF0in.0e7-5grmaminesdie>ve5→0%Lo, fHsoil passes through
• Highly organic soils → Pt

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Soil Classification Systems

Soil Classification Systems

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Soil Classification Systems

TOPIC 3 BASIC CHARACTERISTICS OF SOIL

Soil Compaction

➢ Soil compaction – densification of soil by
reducing air voids by application of
mechanical energy.

➢ The method of mechanically increasing
the density of soil.

➢ It does not involve fluid flow, but
moisture content change.

➢ Compaction is used in construction of
highway embankments, earth dams and
many other engineering structures.

➢ Loose soils must be compacted to
improve their strength by increasing their
unit weight.

➢ The degree of compaction is measured in
terms of its dry unit weight.

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Role of water in compaction

Purpose of compaction ➢ Water is added to the soil during
compaction which acts as a
➢ Increases shear strength of soils lubricating agent on the soil particles.
➢ Increases the bearing capacity of The soil particles slip over each other
and move into a densely packed
foundations position.
➢ Decreases the undesirable
➢ In soils, compaction is a function of
settlement of structures water content
➢ Reduction in hydraulic conductivity
➢ Increasing the stability of slopes • Consider 0% moisture – only
compact so much
on embankments
• Add a little water – compacts better
• A little more water – a little better

compaction
• More water - ?

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Standard Proctor Compaction

Laboratory Compaction Tests

➢ Purpose: Find the Maximum Dry
Unit Weight and corresponding
Optimum Moisture Content

➢ The standard was originally
developed to simulate field
compaction in the laboratory

➢ Two types of tests:

Standard Proctor Test

Modified Proctor Test

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Summary Between Standard Proctor
Test and modified Proctor Test
Modified Proctor Compaction
➢ The modified was developed to Type Standard Modified
Proctor Proctor
simulate larger compaction effort Rammer weight
for more serious loads and bigger Height drop 2.5 kg 4.5 kg
equipment
➢ Using same mould but the No. of soil layers 310mm 450mm
hammer mass is 4.54kg, drop Uses
height 45.7cm and number of 35
layers is 5. No. of blows per
layer Light Heavy
Energy compaction test compaction test

25 blows 25 blows

7.91 joule 21.62 joule

TOPIC 3 BASIC CHARACTERISTICS OF SOIL Result of Compaction Test

Compaction Curve
➢ Compaction curve is plotted by taking

moisture content on x-axis and dry
density on y-axis.
➢ The results are plotted on a graph and
will show the curvilinear relationship
that allows the maximum dry unit
weight and optimum moisture
content.
➢ It is observed that the dry density
increases with an increase water
content till the maximum density is
attained. With further increase in
water content, the dry density
decreases.