Pavement Materials

1. 1
Pavement Materials
Soil
Lec 03
Highway & Traffic Engineering
Maj Anees
Pavement Materials
• Soil
• Aggregate
• Bituminous Materials
• Cement
Lec 03 - Pavement Materials - Soil 3Maj Anees

2. 2
SOIL
Pavement Materials
Outline …….
• Introduction
• Index properties of soil
• Desirable properties of soil as pavement material
• Soil classification systems
• Soil investigation
• Characterization of soil
• Problems in subgrade soil
Lec 03 - Pavement Materials - Soil 5Maj Anees

3. 3
Soil  Introduction
• Soil is a loose mass of minerals available in abundance over
the crust of the earth that is originated from weathering of
the rocks
• Main function is to provide support to the road pavements
• Uses are:
– As sub grade (Lowest layer of a road pavement made up of
compacted soil)
– As one of the ingredients, in the base and sub-base layer of a
pavement
– In road embankments
• The knowledge of behavior of soil is known as
“Characterization of soil”
Lec 03 - Pavement Materials - Soil 6Maj Anees
Soil  Introduction
• Soil horizons are the results of natural
weathering
– O horizon. Loose and partly decayed
organic matter
– A & B horizon constitutes the
weathered zones
– A horizon. Practically a non plastic
silt (mineral mixed with some
humus)
– E horizon. Light colored zone of
leaching
– B horizon. Accumulation of Silty
clay or clay from above
– C Horizon. Parent Material - original
un-weathered rock
Lec 03 - Pavement Materials - Soil 7Maj Anees
O Horizon
A Horizon
E Horizon
B Horizon
C Horizon
Rock

4. 4
Soil  Index Properties
• Soil properties on which their
identification and classification are
based, are known as index properties
– Grain size distribution
– Liquid limit
– Plastic limit
– Plasticity Index
– Shrinkage limit
– Field moisture equivalent – no more in
use
• Soil having high value of liquid limits
and plasticity index are poor as
engineering materials
Lec 03 - Pavement Materials - Soil 8Maj Anees
Atterbeg limits &
Indices
Liquid
State
Liquid Limit
Plastic Limit
Shrinkage Limit
Dry
Plastic
state
Semisolid
state
Solid State
LL – PL = P.I
Soil  Desirable Properties
• Desirable Properties of Soil
– Stability
– Incompressibility
– Permanency of strength
– Min changes in volume
– Good drainage
– Ease of compaction
Lec 03 - Pavement Materials - Soil 9Maj Anees

5. 5
• Common types are:
– Cobble
– Gravel
– Sand
– Silt
– Clay
– Colloids
– Loam. well graded from
course to fine
– Loess. Fine grained aeolian
soil, uniform grain size,
mainly silt, low desity
– Muck. Soft silt of clay high
in organic content
– Peat. Partially decomposed
organic matter
Lec 03 - Pavement Materials - Soil 10Maj Anees
Soil  Types
Clay Silt Sand Gravel Cobble
AASHTO Specifications M 146
802.0.08.002mm
Boulder
200
Soil  Classification
• Classification systems are aimed at categorizing different soils
into groups & subgroups based on their engineering behavior
• Following are few of soil classification systems in use:-
– Textural cl system
– Bermister descriptive cl
– Casagrande soil cl
– Unified Soil Cl System (USCS)
– US public road administration (PRA) cl
– AASHO Soil cl
– Federal Aviation Agency (FAA) cl
– Civil AeronauticAdministration (CAA) cl
– Compaction cl
Lec 03 - Pavement Materials - Soil 11Maj Anees

6. 6
• Dev by US Department of
Agriculture to provide
indication of soils’ ability
to support plant/crop
growth
• Textural classification
system
• Based on relative
proportions of Sand, Silt
and Clay
Lec 03 - Pavement Materials - Soil 12Maj Anees
Soil  Classification  USDA
Soil types by clay, silt and sand composition as used by the USDA
Soil  Classification  AASHTO
• Developed in 1928 by the Bureau of Public Roads
• Currently uses seven major groups of soils, A1 to A7
• Provides a general rating of the soil as a subgrade for road
construction
– Considers grain size distribution and plasticity of fines (P40)
– Coarse grained - granular soils P200 < 35% (A1 to A3 soils)
– Fine grained - silty & clayey soils P200 > 35% (A4 to A7 “ )
– Soils classes are based on elimination using classification table or
plasticity chart
– Group Index is also calculated as a relative group indicator
Lec 03 - Pavement Materials - Soil 16Maj Anees

7. 7
Soil  Classification  AASHO
Lec 03 - Pavement Materials - Soil 17Maj Anees
• AASHO Group Index
– GI=(F-35)[0.2+0.005(LL-40)] + 0.01(F-15)(PI-10)
– F=P 200
– For A-2-6 and A-2-7, use GI=0.01(F-15)(PI-10)
– GI reported in parenthesis as integer If GI<0, use 0
– Higher the GI poorer the soil as subgrade material
Soil  Classification  USCS
• Dev by Casagrande in 1942, widely used by geotechnical engineers
– Considers grain size distribution and plasticity of fines (< P40)
– Coarse Grained: P200 < 50%
– Fine Grained: P200 > 50%
• USCS Symbols
– G – gravel
– M – silt
– O - organic
– W – well graded
– P – poorly graded
– L – low plasticity (LL < 50)
– H – high plasticity (LL > 50)
– S - sand
– C – clay
Lec 03 - Pavement Materials - Soil 22Maj Anees
USCS Plasticity Chart
LL = 35, PI = 15
Soil fines
are Clay

8. 8
Soil  Classification  USCS
Lec 03 - Pavement Materials - Soil 25Maj Anees
Soil  Classification  USCS…..
Lec 03 - Pavement Materials - Soil 26Maj Anees

9. 9
Soil  Classification  Organic Soils
Lec 03 - Pavement Materials - Soil 27Maj Anees
Soil  Investigation
• Preliminary Investigation
– This may include the identification of soil types from
topographical maps, geological maps, soil maps, aerial photos,
satellite images, ground water conditions and examination of
existing road cuttings
– The visual investigation coupled with small amount of
sampling and testing
– Elements of investigation
• Existing topography
• Drainage pattern
• Erosion and vegetation
Lec 03 - Pavement Materials - Soil 30Maj Anees

10. 10
Soil  Investigation
• Detailed Investigations (Field Testing)
– Includes geophysical exploration, test pits and boring,
sampling of soil/rocks, registration of soil profiles and ground
water conditions
– Two geophysical methods Electric resistivity & Seismic
refraction method used for road investigation
– Includes testing of representative samples
• The depth of test pit and boring should be at least one
meter below the purposed sub grade elevation
• Where soft soil is encountered , go down to denser strata
• It is advisable to take a greater no of samples in the field
that can be tested in lab
Lec 03 - Pavement Materials - Soil 31Maj Anees
Soil  Investigation
• Detailed Investigations (Lab Testing)
– Testing of disturbed sample
• Particle size distribution. Important since many properties
such as internal friction, void content, wear resistance and
permeability etc. can be ascertained
• Moisture content. For strengths and deformation
characteristics
• Specific gravity. Water / solids in a given volume of material
• Free swell - Used to verify ty. Is used in the equations
expressing the phase relation of air, swelling tendencies
– Expressed by inc of volume as a %age of initial volume
• Plasticity. use to estimate engineering behavior of clayey soils
Lec 03 - Pavement Materials - Soil 32Maj Anees

11. 11
Soil  Investigation
• Detailed Investigations (Lab Testing)………..
– Testing of disturbed sample……..
• Density - Influences bearing capacity and settlement potential
– Core cutter method and sand replacement method
• Compaction- standard and modified compaction test
• California bearing ratio
• Dynamic cone penetrometer test
– Testing of undisturbed sample
• Consolidation test – is employed to estimate the settlement of
soil under embankment or other structures
• Tri-axial compression test – is used to examine the structural
strength of soil as foundation of structure or in detail studies of
slope study problems
Lec 03 - Pavement Materials - Soil 33Maj Anees
Layered Input Parameters
• Parameters generally used to
characterize the soil are:-
– Resilient Modulus
– Poisson's ratio
– Permeability
Soil Tests
• Soil tests used to ascertain its
suitability for highways
– Shear tests
• Direct shear test
• Triaxial compression test
• Unconfined compression test
• Vane shear test
– Bearing tests
• Plate load tests (Modulus of
subgrade reaction)
– Penetration tests
• CBR
• Cone penetrometer test
Lec 03 - Pavement Materials - Soil 34Maj Anees
Soil  Characterization

12. 12
Soil  Characterization
Resilient Modulus (Mr)
• It is a fundamental material property used to characterize pavement materials
• It is a measure of material stiffness and provides a mean to analyze stiffness of
materials under different conditions, such as moisture, density and stress level
• It is also a required input parameter to pavement design
• closely simulate the material in-situ conditions under traffic loading
• The total resilient (recoverable) axial deformation response of the specimen is
measured and used to calculate the resilient modulus using the following
equation:
– MR =resilient modulus
– σd=stress (applied load / sample cross sectional area)
– εr=recoverable axial strain = Δ L/L
– L=gauge length over which the sample deformation is measured
– Δ L= change in sample length due to applied load
Lec 03 - Pavement Materials - Soil 35Maj Anees
 
r
d
RR EorM



Soil  Characterization
• Resilient Modulus
– In repeated tri-axial load tests, MR, is defined as the ratio of the peak cyclic
deviator stress to the recoverable measured axial strain
• MR = (σ1-σ3) / Єr
– Based on tests on soil and granular materials, empirical formulae suggested
is as under. Unit is (MPa)
• MR = 10 x CBR for CBR ≤ 5%
• MR = 17.6 x CBR
0.64
for CBR > 5%
Lec 03 - Pavement Materials - Soil 36Maj Anees

13. 13
MR
Maj Anees Lec 03 - Pavement Materials - Soil 37
σd = σ1 - σ3
σ1
σ3
Soil  Characterization
• Poisson's Ratio
– When a material is compressed in one direction, it usually tends to expand in
the other two directions perpendicular to the direction of compression. This
phenomenon is called the Poisson effect
– Ratio of lateral strain to axial strain due to axial loads caused by a load
parallel to axis along which Є is measured
– The Poisson ratio is the ratio of the fraction (or percent) of expansion divided
by the fraction (or percent) of compression
– Generally, "stiffer" materials will have lower Poisson's ratios than "softer"
materials
– For most of the cement treated materials (soil cement, cement treated base,
lean concrete base and PCC), the value of µ lies normally between 0.10 &
0.25. value of µ for clays and sands (saturated) are 0.5 & 0.35 respectively
Lec 03 - Pavement Materials - Soil 39Maj Anees

14. 14
Soil  Characterization
Lec 03 - Pavement Materials - Soil 40Maj Anees
ν = εx /εz
ν = (3K - 2G)/(6K + 2G)
E = 2G( 1 + ν)
E = 3K(1 - 2 ν)
Soil  Characterization
• Permeability
– Measure of the ability of a porous material (often, a rock or
unconsolidated material) to allow fluids to pass through it
– Ease with which water flows through soil
– Used for subsurface drainage
– D' Archy's law Q = kiA (coefficient of permeability x
hydraulic gradient x cross sectional area)
– Tests used are constant head, falling head
– Sand has high coefficient of permeability whereas clay has
low coefficient of permeability
Lec 03 - Pavement Materials - Soil 41Maj Anees

15. 15
Soil  Common Subgrade Problems
• Most common subgrade problems are briefly discussed below.
This does not mean that other problems (eg, slope failures,
undermined ground, etc) may not occur, but experience has
shown that the problems discussed are the most common ones
that typically need special attention during the planning and
investigation stage
– Expansive clays
– Collapsible soils
– Dispersive/erodible soils
– Saline soils
– Karst areas
– Soft clays
Maj Anees Lec 03 - Pavement Materials - Soil 49
Soil  Common Subgrade Problems
• Expansive Soil
• Soils which have tendency to swell or expand
• Remedial measures
– Pre-wetting prior to construction of the fill,
– Remove the expansive clay beneath the road structure and
replace it with inert material
– Lime stabilization of the clay to change its expansive property
– Using waterproofing membranes or vertical moisture barriers,
which are generally geo-synthetics
Maj Anees Lec 03 - Pavement Materials - Soil 50

16. 16
Soil  Common Subgrade Problems
• Collapsible soils
– Result from a unique condition in which “bridges” of fine materials
(usually clays or iron oxides) within a framework of coarser and
harder particles (usually quartz) become weak when wet and
collapse under load
• Remedies
– Collapsible soil needs to be wetted up and heavily compacted in
order to disrupt the collapsible fabric
– Prevent the presence of water
– Excavate the material, break down the collapsible structure and any
lumps (using a grid roller where necessary) and then to compact the
layer back into the excavation using conventional rollers with the
appropriate quantity of water in lifts not exceeding about 250 mm
Maj Anees Lec 03 - Pavement Materials - Soil 51
Soil  Common Subgrade Problems
• Dispersive/erodible soils
• Dispersive soils in subgrade lead to significant failures through
piping, tunneling and formation of cavities in structure
• Remedies
– Avoid in fills and remove and replace it in the subgrade
– It is important to manage water flows and drainage in the area
– The presence of sodium as an exchange cat-ion in the clays is the
major problem, treatment with lime or gypsum will allow the
calcium ions to replace the sodium and reduce the problem
– Material be compacted at 2 to 3% above optimum moisture content
to as high a density as possible
– Covering of the soils with non-erodible materials and vegetation
(assisted by geo-synthetics where necessary)
Maj Anees Lec 03 - Pavement Materials - Soil 52

17. 17
Soil  Common Subgrade Problems
• Saline Soils
– It have soluble salts, particularly sulphates and their acids which can
have a serious detrimental effect on the stability/durability of
chemically stabilized materials and asphalt concrete
• Remedies
– As soluble salt problems arise from the accumulation and
crystallization of the salts under the road surfacing and in the upper
base layer, minimization of salts in the pavement layers and subgrade
should be attempted. If the surfacing is sufficiently impermeable
,crystallization will not occur beneath the surfacing
– Construction should proceed as fast as possible to minimize the
migration of salts through the layers
– The addition of lime to increase the pH to in excess of 10.0 will also
suppress the solubility of the more soluble salts
Maj Anees Lec 03 - Pavement Materials - Soil 53
Soil  Common Subgrade Problems
• Karst areas
– Associated with limestone, dolomites and other carbonated rocks
and the occurrence of subsidence and caverns therein, resulting from
dissolution of the carbonate material by slightly acid groundwater
• Remedies
– Sinkholes (when identified or after collapse) are normally filled
with waste rubble or grouted
– Any development on karst areas should be associated with carefully
designed and constructed control measures for wet services, storm
water drainage and particularly for water extraction from the area
through boreholes
– Road drainage must ensure that all water is controlled and moved
through well maintained drains to areas where they are unlikely to
cause subsidence problems
Maj Anees Lec 03 - Pavement Materials - Soil 54

18. 18
Soil  Common Subgrade Problems
• Soft Clay
• Normally alluvial soils and are deposited in estuarial areas and have low shear
strengths, are highly compressible and their low permeability result in time-
related settlement problems
• Remedies
– Road embankments built on soft clays thus need careful control during their construction
to avoid stability failures as pore water pressures increase under the applied loads. It is
recommended that embankments are constructed slowly layer by layer, while monitoring
pore water pressures and additional layers are only added once the pore water pressures
have dissipated adequately
– Despite these measures, long-term settlement continues and problems are often
encountered with large differential settlements between the approach fills founded on the
clays and bridges founded on piles. These long-term differential settlements require
ongoing maintenance to provide an adequate performance of the road.
– The use of the wide range of geosynthetic products as separation layers and to facilitate
and accelerate drainage has contributed to improved construction over such areas in the
past decade or two, and specialist advice in this respect should be obtained.
Maj Anees Lec 03 - Pavement Materials - Soil 55
References
• Text Books
– Highway Engineering by Dr. S.K. Khanna and Dr. C.E.G Justo, 5th
Edition, Chapter 6
– Highway Engineering by Paul H. Wright and Karen K. Dixon, 7th Edition,
Chapter 15
• References
– Traffic and highway engineering by Nicholas J Garber and Lester A Hoel, 3rd
Edition, Chapter 19
– Principles of Pavement Design by E.J.Yoder and M.W.Witczak, 2nd Edition,
Chapter 7 & 8
– Highway Engineering by Clarkson H. Oglesby, 3rd Edition
– AASHTO T 292: Resilient Modulus of Subgrade Soils and Untreated Base/Subbase
Materials
– AASHTO recommended practice for soil classification - M145
– http://www.uwe.ac.uk/geocal/geocal.htm
– http://en.wikipedia.org
Lec 03 - Pavement Materials - Soil 56Maj Anees

19. 19