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PHYSICAL PROPERTIES AND ENGINEERING CLASSIFICATION OF SOIL
CHAPTER 1
§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
Soil formed by rock in different condition after weathering.
transportation 、 deposit
formation processformation condition
physical or mechanical properties
rock
earth
soil
earth
influence
weathering
Soil Formation
Parent Rock
Residual soil
~ in situ weathering (byphysical & chemicalagents) of parent rock
Transported soil
~ weathered andtransported 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 parentrock
Transported Soils
Transported by:
wind
sea (salt water)
lake (fresh water)
river
ice
Special name:
“Aeolian”
“Marine”
“Lacustrine”
“Alluvial”
“Glacial”
§1.2 tri-phase components of soil
vapor phasesolid phase liquid phase+ +
composing soil framework, final effect
significant effect
Soil mass
§1 Physical properties and classification of soil
secondary effect
solid grain
physical state &mechanical characteristics
grading级配
mineral
components
grain shape
1.2.1 solid phase
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 m2. Tiny flakes or needles inshape3. Soil has plasticity only ifit contains clay minerals
Clay minerals• Final product of weathering• Consisting of two distinct structural
units.hydroxyl or
oxygen
silicon
0.26 nm
Silicon tetrahedron
oxygen
aluminium ormagnesium
0.29 nm
Aluminium Octahedron
hexagonalhole
Tetrahedral & OctahedralSheets
For simplicity, we represent silica tetrahedral sheet by:
Si
and alumina octahedral sheet by:
Al
Different Clay Minerals
Different combinations of tetrahedral and octahedralsheets form different clay minerals:
1:1 Clay Mineral (e.g., kaolinite, halloysite):
Different Clay Minerals
Different combinations of tetrahedral and octahedralsheets form different clay minerals:
2:1 Clay Mineral (e.g., montmorillonite, illite)
Kaoliniteused in paints, paper and in pottery and pharmaceuticalindustries
(OH)8Al4Si4O10
AlSi
Typically70-100layers
joined by strong H-bondno easy separation
Al
Si
Al
Si
Al
Si
0.72 nm
joined by oxygensharing
Montmorillonite
also called smectite; expands on contact with water
Si
Al
Si
Si0.96 nmAl
Si
Si
Al
Si
easily separatedby water
joined by weakvan der Waal’s bond
Montmorillonite
Ahighly reactive (expansive) clay
swells on contact with water
high affinity to water
(OH)4Al4Si8O20.nH2O
Bentonite 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 asdrilling mud.
Si
Illite
Si
Al
joined by K+ ions
0.96 nmfit into the hexagonalholes in Si-sheet
Si
Al
Si
Si
Al
Si
Summary
Others Clay Minerals
Chlorite绿泥石 A2:1:1 mineral.
Halloysite埃洛石 kaolinite family
Si Al Al or Mg tubular structure
Vermiculite蛭石 montmorillonite family
swelling clay
Attapulgite凹凸棒石 chain structure
needle-like appearance
Shapes of soil particles
Soil Grain Size
Granular soils orNon-cohesive soils
Cohesivesoils
BoulderClay Sand GravelSilt
0.002 200
Cobble
634.750.075
Grain size (mm)
Fine grainsoils
Coarse grainsoils
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
D
Cc and Cu
Cu : Coefficient of uniformity
D60
D10Cu
Cc :Coefficient of curvature230
(D60D10)Cc
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 aspecific size range
Well graded
Poorly graded
Water in soil is the liquid phase, and its types and quantities have important influence upon the state and porosities of soil.
1.2.2 liquid phase
crystal water : mineral inner water
combined water: water absorbed on soil grain surface
free water: water out of electric field gravitation
soil ice: free water freeze
Absorbed water
• close arrange 、 powerful directing property• density>1g/cm3• freezing point is minus dozens degrees• having solid character• temperature>100°C can vapor
powerful 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
feeble absorbed water
free water
bulk water
capillary water
under gravitation, can flow in soil
• exist between solid and gas • under gravitation and surface tension, can move on soil grain interspace freely
3. soil gas
free gas : connect atmosphere , no great effect on soil properties
closed gas : enhance soil elasticity ; block seepage flow channel
1.2.3 Vapor phase
Clay Fabric
face-to-face contact
Dispersed
edge-to-face contact
Flocculated
§1.3 Soil fabric
coarse-grained soil fabric
•forces among particles:
• mineral component:
gravitation, capillary force
point to point contact 、 point to plane contact
original mineral
§1.4 Phase Relations
Soil is a three phase system:
Solids
Water
Air
Objectives
To compute the masses (or weights) andvolumes of the three different phases in soil
airVa Ma=0
VvM = mass (kg, Mg)
Mt
water MwVw
Vt
W =weight (kN)V = volume (m3)s = soil grains
soilVs Ms
w = watera = airv = voidst = total
Soil Water (Moisture) Content, w (%)
A measure of water present in soil.
air
water
Ma=0
Mw
Va
Vw
VvMW
M S
X 100%w =
MtVt
soilVs MsExpressed as percentage.
Range = 0 ~ >> 100%.
Phase Diagram
Soil Void Ratio, e [-]
A measure of the void volume in soil.
V V
V S
air
water
Ma=0
Mw
Va
Vw
Vve=
MtVt
soilVs Ms
Range = 0.3 ~ > 3
Phase Diagram
Soil Porosity, n [-] or %
Another measure of soil void volume
n= VV
Vt airVa Ma=0
Vv
water Mw
Mt
Vw
Vt
Theoretical range: 0 – 100%soilVs Ms
Degree of Saturation, S %
The percentage of the void volume filled by water.
VW
VV
X 100%air
water
Ma=0
Mw
Va
Vw
VvS=
Range: 0 – 100%
MtVt
Dry
soilVs Ms
Phase Diagram
Saturated
A Simple Example
When
air
water
soil
Vs = Vv and
Va = Vw
e=?
S= ?
n=?
Bulk Density, b[kg/m3, Mg/m3]
Density of the soil in the current state.
Vv
MtVt
Units:
b =
Mg/m3,
Mt
Vt
kg/m3
air
water
soil
Va
Vw
Vs
Ma=0
Mw
Ms
Phase Diagram
Special cases of bulk density -1 1
Dry density (soil voids are filled with air).
airVa Ma=0
Vv
d =?
MtVt
soilVs Ms
Phase Diagram
Special cases of bulk density -2 2
Saturated density (soil voids are filled with water).
waterMwVw
Vv
sat =?
MtVt
soilVs Ms
Phase Diagram
Specific Gravity, Gs [-]
Ratio of solid density and water density
s
wGs
Typical values for soil(inorganic) solids:
air
water w
soil Gsw
Gs = 2.5 – 2.8
Phase Diagram
Useful Equations-1
If we set Vs = 1e
V v air
See
V
S
V w
water Sewt
soil1 Gsw
s
w
M
M
Phase Diagram
Useful Equations-2
If we set Vs = 1
See
MW
M S
w air
water Sew
n soil1 Gsw
VV
Vt
Phase Diagram
Useful Equations-3
Mt
Vt
b
Mt(S 1)
Vt
sat
air
waterSee
Sew
Mt(S 0 )
Vt
d soil1 Gsw
Phase Diagram
Density and Unit Weight
Bulk, saturated, dry and submerged unit weights ()
= g
9.81 m/s2N/m3
kN/m3kg/m3
Mg/m3
A Gentle Reminder
Try not to memorize the equations. Understand thedefinitions, and develop the relations from the phasediagram;
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) andvolume ( (Vs) remain the same at any void ratio;Phase relations do not reflect soil grain sizedistributions
Example 1
A saturated soil has amoisture content of38.0% and a specific air
waterSee
Sew
gravity of solids of2.73. Compute thevoid ratio, porosityand unit weight
soil1(kN/m3) of this soil. Gsw
Phase Diagram
Example 2
On a construction site, the soil bulk
airdensity and water content havebeen measured as = 1.76Mg/m3, w = 10%. In the
waterSee
Sewsubsurface survey report, youneed to report:
d (dry density)
1.
soil12.3 3.4.5.
e (void ratio)n (porosity)S (degree of saturation)
sat(saturated density)
Gsw
Phase Diagram
Exercise
Prove: d= b/(1+w)
Vv
MtVt
air
water
soil
Va
Vw
Vs
Ma=0
Mw
Ms
Relative Density (Dr)ASTM D4253 and D4254
Indication of how densely the grains arepacked in a coarse grain soil.
0
Loosest
100%
Densest
Dr e
emin
emax
emax
Also known as density index (ID) ).
§1.5 physical states and Index
Consistency y of g granular soils:Judged by relative density
Relative Density (%)
0-15
15-35
35-65
65-85
85-100
Consistency Term
Very loose
Loose
Medium dense
Dense
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 consideratepressure
Hard: will not mould under pressure in the hand
Crumbly: breaks up into crumps
Atterberg Limits – for classificationof fines
A set of border line soil water contents thatseparate the different states of a fine grainedsoil
Liquidlimit
Plasticlimit
0 water content
liquidsemi-solid
Shrinkagelimit
brittle-solid
plastic
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 soilremains plastic
Plasticity Index = Liquid Limit – Plastic Limit
Liquidlimit
Shrinkagelimit
Plasticlimit
0water content
plastic
Plasticity Index PI = LL-PL:Indicator of soil plasticity
PI
0 0-3 3
3-15
15-30
>30
Dry strength
Very low
Slight
Medium
High
Classification
Non plastic
Slightly plastic
Medium plastic
Highly plastic
Liquidity Index (IL)
I L wn
LL
PL
PL
Wn = natural soil moisture content
LLShrinkage PL0w, %
limit
PI
IL : Indicator of soil liquefiability
IL
<0
0 <IL < 1
IL > 1
wn
wn < PL
PL < wn < LL
wn > LL
Soil condition
Non-plastic, non-liquefiable
Plastic, non-liquefiable
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.
Compaction of Earth WorksRef: Coduto Chapter 6
1
§1.6 soil compaction
What is compaction?
A simple ground improvement technique,where the soil is densified through externalcompaction effort.
Compactioneffort
+ water =
2
Compaction: reduce air and wateri in soil il
3
Field CompactionDifferent types of rollers (clockwisefrom right):
Vibratory roller
Smooth-wheel roller
Pneumatic rubber tired roller
Sheep-foot roller
4
Field CompactionVibrating Plates
5
for compacting very small areaseffective for granular soils
Field CompactionSmooth Wheeled Roller
•
•
Compacts effectivelyonly to 200-300 mm;Place the soil inshallow layers (lifts)
6
Field CompactionImpact Roller
Provides deeper(2-3m)compaction. e.g.,air field
7
Field CompactionSheep-foot Roller
Provides kneading actionVery effective on clays
8
Advantage of sheep- -foot roller incompaction of clay liners
9
Pounder (Tamper)
Dynamic Co ompaction
Suitable for granular soils, land fillsand karst terrain with sink holes.
solution cavities inlimestone
Crater created by the impact(to be backfilled)
10
11
d)
dens
ity
( D
ryd
Compaction Curve
Increasing compactionenergy results in:
• Lower optimum
E2 (>E1)water content
• Higher maximum drydensity
E1
Water content
12
Compaction Curve
Gs w
1 wGs /S d
b
1 w d
13
Effect of moisture content duringcompaction on soil fabric in clays
14
Laboratory Compaction Test
Standard Proctor:
• 3 layers
• 25 blows per layer
• 2.7 kg hammer
• 300 mm drop
Modified Proctor:
• 5 layers
• 25 blows per layer
• 4.9 kg hammer
• 450 mm drop
1000 ml compaction mould (1.0 x 10-3 m3)
15
Laboratory yCompaction
Test
16
Compaction Control
17
Measure density and water contentin 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 soilmoisture content
– Prescriptive specifications – contractor builds a test pad toestablish compaction effort required to achieve the end result ,including
• the compaction equipment
• thickness of soil layers
• number of travels
21
• soil water content, , etc.
Shrink and Swell from Cut to FillMake sure the definition is clear to all parties on the job;Cut and fill specifications must be careful determinedShrinkage factor is sensitive to errors – it could lead to serious
economic problems during a job
22
Shrinkage Factor
1)100%SF ( d fill
dcut
• Make sure the definition is clear to all parties on thejob
• Cut and fill specifications must be careful determined
• SF calculations are sensitive to errors – it could leadto serious economic problems during a job
23
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
§1.7 soil classification
USCS Symbols
% of fines
f fine grain soilscoarse grain soils
0 5 12 50 100
XA
YB
e.g., CH, ML
XY
e.g., SM, GC
B: Plasticity
e.g., GP
SW
XA-XY
e.g., SP-SC, GW-GM
X: Coarse
G = Gravel
S = Sands
(Sieve analysis)
Y: Fines
M = Silts
C = Clays
(C’s Chart)
A: Gradation
W = well graded
P = poorlygraded
(Cc and Cu)
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)
Codutopp. 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 arelatively small number of groups suchthat the relation of each soil to the manydivergent problems of applied soilmechanics will be adequately addressed.”
Arthur Casagrade 1948