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SOIL AS A ROAD
CONSTRUCTION MATERIAL
Presentation by
R.K.SWAMI
Scientist EE-II
Geotechnical Engineering Division
,
Introduction
Soil - mineral matter formed by the
disintegration of rocks due to action of water,
frost, temperature, pressure or by plant or
animal life
Soil is an integral part of road pavement
Soil is used as fill material for embankments,
in its natural form (gravel or sand) or in
processed form in base or sub-base
Knowledge of soil properties is necessary to
select the embankment material, design
pavement structure and drainage system
Characteristics of soil
• BIS Limits of particle size
– Gravel 80 to 4.75 mm
– Sand
• Coarse
4.75 to 2.00 mm
• Medium 2.00 to 0.475 mm
• Fine
0.475 to 0.075 mm
– Silt
0.075 to 0.002 mm
– Clay
Less than 0.002 mm
• Soil texture - Appearance or feel
• Clay minerals
– Electrochemically active
– Crystal sheets in clay - Tetrahedral or silica
and Octahedral or alumina
Desirable properties of soil
 Stability
 Incompressibility
 Permanency of strength
 Minimum changes in volume &
stability
 Good drainage
 Ease of compaction
Undesirable types of soil





Highly plastic soils
Soils which favour capillary rise of water
Frost susceptible soils
Organic and sulphatic soils
Permissible limits
 Sodium sulphate - 0.2 per cent maximum
 Organic matter - 1.0 per cent maximum
Soil survey
 The objective of soil survey is to
determine the soil types
occurring along alignment and to
locate the sources of borrow soil
for embankments
 Soil sampling at an interval of
200 m
 Soil samples to be evaluated for
different geotechnical properties
Types of soil in India





Alluvial soils
Fine sands
Coastal soils
BC soils
Red gravelly soils
Types of soil in India
Soft aggregate availability
Natural Aggregates
•
•
•
•
•
•
•
Gravel- Pit Gravel, River Gravel
Laterite
Kankar
Moorum
Soft stone
Dhandla
Shale
Artificial Aggregates
•
•
•
•
Bricks
Slag
Crushed Cement Aggregate
Brick Ballast
Shapes of granular particles
Field identification of soils
• Coarse grained soils - gravel and sand
– Moorum look like gravels but fine content is
more
– Sands vary in texture from coarse to fine but
exhibit no cohesion
• Fine grained soils - silt and clay
– Dry strength test
– Shaking test
– Plasticity test
– Dispersion test
• Organic soils
Field identification of soils
Clay
Moorum with
excessive fines
Silt
Moorum
Sand
Gravel
Index properties of soil
• Grain size analysis
• Liquid limit
• Plastic limit
Grain size analysis
 Important for classifying and
identifying soil
 Dry sieve analysis - for particles
larger than 75 micron
 BIS specifies a set of 12 sieves
 Mechanical shaker or manual
shaking as per availability
Grain size analysis (Contd)
 Sedimentation analysis for particles
finer than 75 micron sieve
 Types of gradations - well graded,
poorly graded and gap graded
 Coefficient of uniformity - shape
parameter Cu = D60/D10
 Poorly graded soils Cu = 2 or 3, well
graded soils Cu = 15 or more
 Coefficient of curvature
Cc =(D30 )2/ D10XD60
Cc = 1 to 3 for well graded soil
Cu = greater than 4 for gravels
and 6 for sand
Grain size analysis (Contd)
Liquid limit
 Plasticity is an important property of clayey
soils
 Minimum moisture content at which a soil
will flow when subjected to a very small
shearing force
 Boundary between liquid and plastic states
 Determined by using Casagrande
apparatus or cone penetrometer
 Soils with high liquid limit are unsuitable as
embankment material
Plastic limit
 Minimum moisture content at which a soil
mass remains in plastic state
 Boundary between plastic and semi-solid
state
 Laboratory test is to roll the soil into thread
of 3 mm diameter
 Plasticity index = Liquid limit - Plastic limit
 PI - Basis for soil classification
Consistency limits
Characetristic
Dry strength
Soils at equal
LL with
increasing PI
Increases
Soils at equal
PI with
increasing LL
Decreases
Permeability
Decreases
Increases
Compressibility About the
same
Rate of volume Decreases
chanege
Increases
--
Soil classification
A soil is given the name of the constituent
that has significant influence on its
behaviour
Other constituents are indicated by
adjectives
Soil classification - means to understand
behaviour of soil mass
Does not consider the properties of intact
material
Soil classification
Textural classification based on grain size
 IS System
System based on grain size, liquid limit and
plasticity index
 HRB Classification
 Unified soil classification
Effect soil content & size of aggregate on CBR
Mechanical stabilisation
• Correctly proportioned material
(aggregate and soil) when compacted,
form a mechanically stabilised layer
• Process involves
– Proportioning
– Compaction
• Successfully applied for sub-base and
base course, and also used as surface
course for low cost roads
Mechanical stabilisation
Design of mechanically stabilised mixes
Combining two materials based on sieve analysis
Numerical
difference
between
material A
& average
8
26
33
32
83
7
Material Sieve
A
size
(Percent
Passing)
Limits
Average Material
B
(Percent
Passing)
100
98
94
83
72
55
17
100
80-100
55-80
40-60
30-50
15-30
5-15
100
90
68
50
40
22
10
40 mm
20 mm
10 mm
4.75 mm
2.36 mm
600 
75 
Total= 139
100
73
55
42
35
21
9
Numerical
difference
between
material B
& average
17
13
8
5
1
1
Total = 45
A:B = 45:139 (1:3)
Combining two materials based on plasticity properties
Material A =
______SB (P – PB) ____
SB(P – PB) – SA(P – PA)
Rothfuch method for design of soilsoil-aggregate mixes
Rothfuch method for design of soilsoil-aggregate mixes
COMPACTION OF SOIL
• Pavement failures due to settlement of
embankment fill and sub grade
• Proper quality control during
construction adopting MOSRTH
specifications
Soil compaction
• Compaction process
• Purpose of a laboratory compaction
test
• Difference between compaction and
consolidation
• Compaction of cohesion less soils
• Compaction of fine-grained cohesive
soils
Objectives of soil compaction
• Reduction in frost susceptibility
• Increase in strength
• Reduction in compressibility
• Reduction in tendency for
subsequent changes in moisture
content
• Reduction in erodability
Standard/Modified Proctor
Compaction Test
• Significance
• To determine:
 Optimum quantity of water (OMC)
with which soil shall be compacted in
the field
 Maximum achievable density (MDD)
in the field
Laboratory compaction (Proctor)
test
• Standard compaction
(Part 7) -1980)
(IS:2720
• Modified compaction
(Part 8) -1983)
(IS:2720
• Comparison of compaction curves
• Soil samples susceptible to crushing
Comparison of Compaction Tests
Standard Test
Modified Test
Soil passing 20 mm/37.5 mm IS
sieve
Soil compacted in 3 layers, 25
blows/56 blows
Soil passing 20 mm/37.5 mm IS
sieve
Soil compacted in 5 layers, 25
blows/56 blows
Soil compaction by 2.6 kg
hammer, 31 cm ht. Of fall
Soil compaction by 4.89 kg
hammer 45 cm ht. Of fall
Used for Internal roads in Urban
areas and village roads
depending upon the traffic
Adopted by MORTH
specifications
Used for NH, SH, MDR and ODR
Factors influencing compaction
• Type of soil
– Gradation (Well-graded/Uniformlygraded)
– Clayey soil
– Silty soil
– Sandy soil
– Gravel
Moisture-density relationship for
Moisturedifferent types of soils
Factors influencing compaction
(contd.)
• Moisture content
– Dry of optimum
– Optimum
– Wet side of optimum
• Compactive effort
– Energy applied per unit weight of soil
• Weight of rammer, height of fall, number
of blows
• Weight of roller, number of passes
Moisture--density relationship
Moisture
Effect of compaction on soil
properties
• Unconfined compressive strength
• California Bearing Ratio (C.B.R)
– Unsoaked C.B.R
– Soaked C.B.R
• Permeability
• Settlement
EARTHWORK FOR
EMBANKMENT/SUBGRADE (Contd.)
• Field density control




•
Core cutter method
Sand replacement method
Non-destructive methods, Nuclear density
gauge
Relative compaction
 Field dry density x 100
 Laboratory density
Field compacting machinery
• Compactors
 Smooth wheel rollers
 Sheepsfoot rollers
 Pneumatic tyred rollers
 Vibratory rollers
 Other compacting equipments
 Small vibratory rollers
 Plate vibrators
 Rammers
Field compacting machinery
(Contd)
• Smooth wheel roller
– Used for compacting subgrade, base and asphaltic
surfaces
– Suitable for compacting gravels, sand, and crushed rock
– 8 to 10 tonne rollers
– Appropriate speed of the roller should be 3 - 6 km/h.
Field compacting machinery
(Contd)
• Sheepsfoot roller
– Used in road and earthen dam works
– Suitable for compacting heavy clays and silty clays
– Important parameters affecting compaction
• Weight of roller
• Area of each foot
• Number of foots/lugs in contact with the ground at any
time
• Contact area of the foot
Field compacting machinery
(Contd)
– Pneumatic tyred rollers
• Used for both earthwork and bituminous
works
• Suitable for compacting cohesion less
gravel, sand and cohesive soils
• Important parameters affecting compaction
– Tyre inflation pressure
– Area of contact
Field compacting machinery
(Contd)
•
Vibratory plate compactors
– Useful for small road works and narrow areas such as trench
backfilling
– Suitable for compacting thin layers
– Can be tractor-towed
•
Rammers
– Provide impact load
– Suitable for compacting small areas, back filling of trenches in
foundations
– Suitable for compacting cohesive as well as non-cohesive soils
– Operated manually (driven by petrol engines)
Field compacting machinery
(Contd)
•
Vibratory rollers
– Higher compaction level can be achieved with minimum work
– Compaction can be done up to greater depths
– Output is many times more than conventional rollers
– Suitable for compacting sand and gravels
– Important parameters affecting compaction
• Dead load
• Frequency
• Amplitude
• Area of contact
Lift thickness during
compaction
• Depends on different factors
– Type of roller
– Weight of roller
– Type of soil
– Number of passes
– Prevailing moisture content
– Degree of compaction required
Earthwork for
embankment/subgrade
• Suitability of materials
– Free from peat, perishable and other organic
material
– Should not be spontaneously combustible
– LL less than 70, PI less than 45
– Soils having salts are not suitable
– Free Swell Index more than 50 % should not be
used
– Total sulphate content more than 0.5 % must be
avoided
Earthwork for
embankment/subgrade
(contd.)
• Size of material
– Maximum size of clod should be less than 75
mm in embankment fill
– Maximum size of clod should be less than 50
mm in subgrade
– Maximum particle size should be less than
two third of compacted layer thickness
Density requirements for embankment and subgrade
(MOSRTH specifications)
S.No
Type of work
Maximum
laboratory dry unit
weight when
tested as per IS:
2720 (Part 8)
1
Embankments up to 3
metres height, not
subjected to extensive
flooding
Not less than 15.2
kN/cu.m
2
Embankments exceeding
3 metres height or
embankments of any
height subject to long
periods of inundation
Not less than 16.0
kN/cu.m
3
Subgrade and earthen
shoulders/verges/backfill
Not less than 17.5
kN/cu.m
Compaction requirements for embankment and subgrade
(Rural roads)
S.No.
Type of work/material
Relative compaction
as percentage of max.
laboratory dry density
1.
GSB and stabilised subbase
Not less than 98 %
as per IS: 2720 (Part 8)
2.
Embankment
Not less than 97 % as
per IS: 2720 (Part 7)
3.
Subgrade (Natural
soil or stabilised soil, 30
cm in two layers) and
earthen shoulders
Not less than 100 % as
per IS: 2720 (Part 7)
Compaction requirements for embankment and subgrade
(MORTH specifications)
S.No.
• of work/material
Type
Relative compaction as
percentage of max.
laboratory dry density as
per IS: 2720 (Part 8)
1
GSB and stabilised sub-base
Not less than 97
2
Embankment
Not less than 95
3
Expansive clays
(a) Subgrade and 500 mm portion just below
the sub grade
(b) Remaining portion of embankment
Not allowed
Not less than 90
Density requirements for embankment and subgrade
(MOSRTH specifications)
S.No
Type of work
Maximum
laboratory dry unit
weight when tested
as per IS: 2720 (Part
7)
1
Embankments up to 3
metres height, not
subjected to extensive
flooding
Not less than 14.4
kN/cu.m
2
Embankments exceeding
3 metres height or
embankments of any
height subject to long
periods of inundation
Not less than 15.2
kN/cu.m
3
Subgrade and earthen
shoulders/verges/backfill
Not less than 16.5
kN/cu.m
Moisture density curves for different type of soils
Tandem
vibratory
roller
Static
roller
Vibratory
roller(L&T)
Vibratory
roller
(Escorts)
& water
tanker
Thank you