CHAPTER 1
PHYSICAL PROPERTIES AND
ENGINEERING CLASSIFICATION OF SOIL
§1 Physical properties and classification of soil
§1.1 formation of soil
§1.2 tri-phase components of soil
§1.3 soil fabric
§1.4 phase relations
§1.5 physical states and Index
§1.6 soil compaction
§1.7 soil classification
§1.1 formation of soil
formation process
formation condition
influence
physical or
mechanical
properties
Soil formed by rock in different condition after
weathering.
rock
soil
weathering
earth
transportation 、deposit
earth
Soil Formation
Parent Rock
Residual soil
~ in situ weathering (by
physical & chemical
agents) of parent rock
Transported soil
~ weathered and
transported far away
by wind, water and ice.
Residual Soils
Formed by in situ weathering of parent rock
Soil grain sizes vary in large range
Mineralogy is dependent of parent
rock
Transported Soils
Transported by:
Special name:
wind
“Aeolian”
sea (salt water)
“Marine”
lake (fresh water)
“Lacustrine”
river
“Alluvial”
ice
“Glacial”
§1 Physical properties and classification of soil
§1.2
tri-phase components of soil
Soil mass
solid phase +liquid phase+vapor phase
secondary effect
composing soil framework, final effect
significant effect
1.2.1 solid
phase
solid grain
grading级配
mineral
components
grain shape
physical state &mechanical characteristics
Minerals
•
Minerals are crystalline materials and make up
the solids constituent of a soil. The mineral
particles of fine-grained soils are platy. Minerals
are classified according to chemical composition
and structure.
• Original mineral ： quartz, feldspar, isinglass,
hornblende and pyroxene.
• Secondary mineral ： consists mainly of clay
mineral
Clay Minerals
1. Sizes smaller than 2 m
2. Tiny flakes or needles in
shape
3. Soil has plasticity only if
it contains clay minerals
Clay minerals
• Final product of weathering
• Consisting of two distinct structural
units.
hydroxyl or
oxygen
oxygen
aluminium or
magnesium
silicon
0.26 nm
Silicon tetrahedron
0.29 nm
Aluminium Octahedron
hexagonal
hole
Tetrahedral & Octahedral
Sheets
For simplicity, we represent silica tetrahedral sheet by:
Si
and alumina octahedral sheet by:
Al
Different Clay Minerals
Different combinations of tetrahedral and octahedral
sheets form different clay minerals:
1:1 Clay Mineral (e.g., kaolinite, halloysite):
Different Clay Minerals
Different combinations of tetrahedral and octahedral
sheets form different clay minerals:
2:1 Clay Mineral (e.g., montmorillonite, illite)
Kaolinite
used in paints, paper and in pottery and pharmaceutical
industries
Typically
70-100
layers
joined by strong H-bond
no easy separation
(OH)8Al4Si4O10
Al
Si
Al
Si
0.72 nm
Al
Si
Al
Si
joined by oxygen
sharing
Montmorillonite
 also called smectite; expands on contact with water
Si
Al
Si
Si
easily separated
by water
joined by weak
van der Waal’s bond
Al
Si
Si
Al
Si
0.96 nm
Montmorillonite
 Ahighly reactive (expansive) clay
 (OH)4Al4Si8O20.nH2O
Bentonite
swells on contact with water
high affinity to water
 montmorillonite family y
 used as drilling mud, in slurry trench walls,
stopping leaks
Montmorillonite
 Montmorillonites have very high specific surface,
cation exchange capacity, and affinity to water.
They form reactive clays.
 Montmorillonites have very high liquid limit (100+),
plasticity index and activity (1-7).
 Bentonite (a form of Montmorillonite) is frequently used as
drilling mud.
Illite
Si
joined by K+ ions
fit into the hexagonal
holes in Si-sheet
Al
Si
Si
Al
Si
Si
Al
Si
0.96 nm
Summary
Others Clay Minerals
Chlorite绿泥石
 A2:1:1 mineral.
Si
Al
Al or Mg
Vermiculite蛭石
 montmorillonite family
swelling clay
Halloysite埃洛石
 kaolinite family
tubular structure
Attapulgite凹凸棒石
 chain structure
needle-like appearance
Shapes of soil particles
Soil Grain Size
Cohesive
soils
Clay
Granular soils or
Non-cohesive soils
Sand
Silt
0.002
0.075
Gravel
4.75
Grain size (mm)
Fine grain
soils
Coarse grain
soils
Boulder
Cobble
63
200
Grain Size Distribution (GSD)
Determination of GSD:
• In coarse grain soils …... By sieve analysis
In fine grain soils
…... By hydrometer analysis
hydrometer
stack of sieves
sieve shaker
soil/water suspension
Sieve Analysis
Hydrometer Analysis
Grain size distribution curve
Cc and Cu
Cu : Coefficient of uniformity
D60
Cu 
D10
Cc :Coefficient of curvature
Cc 
D
2
30
(D60D10)
D60 is the diameter of
the soil particles for
which 60% of the
particles are finer.
Well or Poorly Graded Soils
Well Graded Soils
Wide range of grain sizes
Gravels: Cc = 1-3 & Cu >4
Sands: Cc = 1-3 & Cu >6
Poorly Graded Soils
Two special cases:
(a) Uniform soils – grains of same size
(b) Gap graded soils – no grains in a
specific size range
Well graded
Poorly graded
1.2.2
liquid phase
Water in soil is the liquid phase, and its types
and quantities have important influence upon
the state and porosities of soil.
crystal water :
mineral inner water
combined water:
free water:
water absorbed on soil grain surface
water out of electric field gravitation
soil ice: free water freeze
Absorbed water
powerful absorbed water
• close arrange、powerful directing
property
• density>1g/cm3
• freezing point is minus dozens degrees
• having solid character
• temperature>100°C can vapor
feeble absorbed water
•
outside powerful combined water，
inside electric-field attractive force
• can move in the effect of outside force
• not remove as a result of gravitational
force ，having viscidity
bulk water
under gravitation, can flow in soil
free water
• exist between solid and gas
capillary water
• under gravitation and surface tension,
can move on soil grain interspace freely
1.2.3
3.
Vapor phase
soil
gas
free gas：connect atmosphere，no great effect on soil properties
closed gas：enhance soil elasticity；block seepage flow channel
§1.3 Soil fabric
Clay Fabric
edge-to-face contact
Flocculated
face-to-face contact
Dispersed
coarse-grained soil fabric
point to point contact 、point to plane contact
•forces among particles:
• mineral component:
gravitation，capillary force
original mineral
§1.4 Phase Relations
 Soil is a three phase system:



Solids
Water
Air
Objectives
 To compute the masses (or weights) and
volumes of the three different phases in soil
M = mass (kg, Mg)
W =weight (kN)
V = volume (m3)
s = soil grains
w = water
a = air
v = voids
t = total
Va
air
Vw
water
Ma=0
Vv
Mw
Mt
Vt
Vs
soil
Ms
Soil Water (Moisture) Content, w (%)
A measure of water present in soil.
MW
w=
MS
X 100%
Va
air
Vw
water
Ma=0
Vv
Mw
Mt
Vt
Expressed as percentage.
Vs
soil
Range = 0 ~ >> 100%.
Phase Diagram
Ms
Soil Void Ratio, e [-]
A measure of the void volume in soil.
VV
e=
VS
Va
air
Vw
water
Ma=0
Vv
Mw
Mt
Vt
Vs
soil
Range = 0.3 ~ > 3
Phase Diagram
Ms
Soil Porosity, n [-] or %
Another measure of soil void volume
V
V
n=
Vt
Va
air
Vw
water
Ma=0
Vv
Mw
Mt
Vt
Theoretical range: 0 – 100%
Vs
soil
Ms
Degree of Saturation, S %
The percentage of the void volume filled by water.
VW
S=
VV
X 100%
Va
air
Vw
water
Ma=0
Vv
Mw
Mt
Vt
Range: 0 – 100%
Vs
Dr
y
soil
Saturate
d
Phase Diagram
Ms
A Simple Example
When
Vs = Vv and
Va = Vw
air
water
e=?
S= ?
n=?
soil
Bulk Density, b[kg/m3, Mg/m3]
Density of the soil in the current state.
Mt
b =
Vt
Units: Mg/m3, kg/m3
Va
air
Vw
water
Ma=0
Vv
Mw
Mt
Vt
Vs
soil
Phase Diagram
Ms
Special cases of bulk density -1 1
Dry density (soil voids are filled with air).
d =?
Va
air
Ma=0
Vv
Mt
Vt
Vs
soil
Phase Diagram
Ms
Special cases of bulk density -2 2
Saturated density (soil voids are filled with water).
sat =?
Vv
Vw
water
Mw
Mt
Vt
Vs
soil
Phase Diagram
Ms
Specific Gravity, Gs [-]
Ratio of solid density and water density
s
Gs 
w
air
water w
Typical values for soil
(inorganic) solids:
soil Gsw
Gs = 2.5 – 2.8
Phase Diagram
Useful Equations-1
If we set Vs = 1
e 
V v 
S 
V
w
V
t
air


M
s
M
w
e


Se
water
Sew
1
soil
Gsw
Phase Diagram
Useful Equations-2
If we set Vs = 1
M
W
w

MS
V
V
n

Vt
air
e
Se
water
Sew
1
soil
Gsw
Phase Diagram
Useful Equations-3
b  Mt 
Vt
Mt(S 1) 
sat 
Vt
Mt(S  0 ) 
d 
Vt
air
e
Se
1
water
soil
Phase Diagram
Sew
Gsw
Density and Unit Weight
 Bulk, saturated, dry and submerged unit weights ()
 = g
N/m3
kN/m3
9.81 m/s2
kg/m3
Mg/m3
A Gentle Reminder
 Try not to memorize the equations. Understand the
definitions, and develop the relations from the phase
diagram;
 Assume GS (2.6-2.8) if the soil is natural and inorganic
(unless you are required to calculate it!);
 Do not mix densities and unit weights;
 Soil grains are incompressible. Their mass (Ms) and
volume ( (Vs) remain the same at any void ratio;
 Phase relations do not reflect soil grain size
distributions
Example 1
A saturated soil has a
moisture content of
38.0% and a specific
gravity of solids of
2.73. Compute the
void ratio, porosity
and unit weight
(kN/m3) of this soil.
air
e
Se
water
1
soil
Phase Diagram
Sew
Gsw
Example 2
On a construction site, the soil bulk
density and water content have
been measured as  = 1.76
Mg/m3, w = 10%. In the
subsurface survey report, you
need to report:
air
e
Se
water
Sew
1
soil
Gsw
1. d (dry density)
2. e (void ratio)
3 3.n (porosity)
4. S (degree of saturation)
5. sat(saturated density)
Phase Diagram
Exercise
Prove: d= b/(1+w)
Va
air
Vw
water
Ma=0
Vv
Mw
Mt
Vt
Vs
soil
Ms
§1.5 physical states and Index
Relative Density (Dr)
ASTM D4253 and D4254
Indication of how densely the grains are
packed in a coarse grain soil.
0
100%
Loosest
Densest
Dr 
emax
emax
e
emin
Also known as density index (ID) ).
Consistency y of g granular soils:
Judged by relative density
Relative Density (%)
0-15
15-35
Consistency Term
Very loose
Loose
35-65
Medium dense
65-85
Dense
85-100
Very dense
Fines in Soil
Fines: Soil solids passing #200 Sieve (< 74 m)
Consistency of fines:
Very soft: exudes between fingers
Soft: very easy to mould and sticks to hand
Firm: moulds easily with moderate pressure
Very firm: moulds only with considerate
pressure
Hard: will not mould under pressure in the hand
Crumbly: breaks up into crumps
Atterberg Limits – for classification
of fines
A set of border line soil water contents that
separate the different states of a fine grained
soil
0
Plastic
limit
Shrinkage
limit
brittlesolid
semisolid
Liquid
limit
plastic
water content
liquid
Atterberg Limits – 3 components
Liquid Limit (wL or LL):
Clay flows like liquid when w > LL
Plastic Limit (wP or PL):
Lowest water content where the clay is still plastic
Shrinkage Limit (wS or SL):
At w<SL, no volume reduction on drying
Measure Liquid Limit (LL)
Measure Plastic Limit (PL)
Plasticity Index (PI)
Range of water content over which the soil
remains plastic
Plasticity Index = Liquid Limit – Plastic Limit
0
Shrinkage
limit
Plastic
limit
Liquid
limit
plastic
water content
Plasticity Index PI = LL-PL:
Indicator of soil plasticity
PI
Classification
Dry strength
0 0-3 3
Non plastic
Very low
3-15
Slightly plastic
Slight
15-30
Medium plastic
Medium
>30
Highly plastic
High
Liquidity Index (IL)
IL 
wn
PL
LL
PL
Wn = natural soil moisture content
0
Shrinkage
limit
PL
LL
PI
w, %
IL : Indicator of soil liquefiability
IL
wn
Soil condition
<0
wn < PL
Non-plastic, nonliquefiable
0 <IL < 1
PL < wn < LL
Plastic, non-liquefiable
IL > 1
wn > LL
Liquefiable
This is a soil profile from
a site in Gloucester,
Ontario. The Soil can
be divided into two
layers: layer 1: A, B,
C, D and layer 2: E.
1. What can we conclude
from the inspection of
the soil profile?
2. Estimate the liquidity
index for Layer 2.
§1.6 soil compaction
Compaction of Earth Works
Ref: Coduto Chapter 6
1
What is compaction?
A simple ground improvement technique,
where the soil is densified through external
compaction effort.
Compaction
effort
+ water =
2
Compaction: reduce air and water
i in soil il
3
Field Compaction
Different types of rollers (clockwise
from right):
Smooth-wheel roller
Vibratory roller
Pneumatic rubber tired roller
Sheep-foot roller
4
Field Compaction
Vibrating Plates


for compacting very small areas
effective for granular soils
5
Field Compaction
Smooth Wheeled Roller
•
•
Compacts effectively
only to 200-300 mm;
Place the soil in
shallow layers (lifts)
6
Field Compaction
Impact Roller

Provides deeper
(2-3m)
compaction. e.g.,
air field
7
Field Compaction
Sheep-foot Roller


Provides kneading action
Very effective on clays
8
Advantage of sheep- -foot roller in
compaction of clay liners
9
Dynamic Co ompaction
Suitable for granular soils, land fills
and karst terrain with sink holes.
Pounder (Tamper)
solution cavities in
limestone
Crater created by the impact
(to be backfilled)
10
11
d
d) density
( Dry
Compaction Curve
Increasing compaction
energy results in:
E2 (>E1)
• Lower optimum
water content
• Higher maximum dry
density
E1
Water content
12
Compaction Curve
d 
b
1 w
Gs w
d 
1 wGs /S
13
Effect of moisture content during
compaction on soil fabric in clays
14
Laboratory Compaction Test
Standard Proctor:
Modified Proctor:
• 3 layers
• 5 layers
• 25 blows per layer
• 25 blows per layer
• 2.7 kg hammer
• 4.9 kg hammer
• 300 mm drop
• 450 mm drop
1000 ml compaction mould (1.0 x 10-3 m3)
15
Laboratory y
Compaction
Test
16
Compaction Control
17
Measure density and water content
in field
18
Nuclear meter
19
20
Compaction Specifications
– Design specifications
• For sands and gravels: relative density (ID)
• For fine grained soils, relative compaction ( R) and soil
moisture content
– Prescriptive specifications – contractor builds a test pad to
establish compaction effort required to achieve the end result ,
including
• the compaction equipment
• thickness of soil layers
• number of travels
• soil water content, , etc.
21
Shrink and Swell from Cut to Fill
Make sure the definition is clear to all parties on the job;
Cut and fill specifications must be careful determined
Shrinkage factor is sensitive to errors – it could lead to serious
economic problems during a job
22
Shrinkage Factor
 d fill
SF  (
1)100%
 dcut
• Make sure the definition is clear to all parties on the
job
• Cut and fill specifications must be careful determined
• SF calculations are sensitive to errors – it could lead
to serious economic problems during a job
23
§1.7 soil classification
United Soil Classification System
(USCS)
•Developed by A. Casagrande in 1948
•ASTM Standard D2487
•Commonly used by geotechnical engineers
•Require two sets of tests for soil classification, i.e.
•Gradation (sieve and hydrometer) tests
•Atterberg limits (PL, LL) tests
USCS Symbols
coarse grain soils
f fine grain soils
% of fines
0
5
12
XY
50
100
YB
e.g., CH, ML
e.g., SM, GC
XA
e.g., GP
XA-XY
SW
e.g., SP-SC, GW-GM
B: Plasticity
A: Gradation
X: Coarse
Y: Fines
G = Gravel
M = Silts
S = Sands
C = Clays
P = poorly
graded
(Sieve analysis)
(C’s Chart)
(Cc and Cu)
W = well graded
H: LL > 50
L: LL < 50
(C’s Chart)
Casagrande’s s Plasticity Chart
U-line: IP = 0.9(wL – 8)
A-line: IP = 0.73 (wL – 20)
Fine grained soils (> 50% passing #200 sieve)
Coduto pp. 175
Coarse grained soils (< 50% passing #200 sieve)
Coduto
pp. 178
Other considerations -1
Other considerations -2
Other considerations -3
Other considerations -4
Applicability and Limitations
“ It is not possible to classify all soils into a
relatively small number of groups such
that the relation of each soil to the many
divergent problems of applied soil
mechanics will be adequately addressed.”
Arthur Casagrade 1948