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8/16/2019 Highway Engineering Design_Pavement Design
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Dr. Wasala Bandara
1
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Pavement is defined as a road or highway with hard, smooth,and leveled surface made using a suitable material such as
Portland cement concrete or asphalt concrete
Asphalt concrete pavement Portland cement concrete pavement
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In the west; Romans were the pioneer road makers, who use elaborate techniquesas far back as 312 B.C. They construcred the three kinds of roads as follows:
Levelled earth roads
Compacted gravel road
Stone block-paved roads
The Romens practiced the removal of all soft material under a pavementand building up the road from the hard stratum. Therefore these road hadpavement thickness varying from 0.75m to 2.5m.
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The next stage in the development of road making came in the 18th
century whenthe French engineer Tresaguset (1716-1796) introduced the concept of crosschamber for surface water drainage.
This method of construction consisted of preparing a convex road bed or subgrade and laying two layers of hand-packed foundation stones.
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Telford (1757-1834), the founder and first president of the Institution of CivilEngineers proposed a new method of construction in the early 19th century.
He believed in the principle of effecting surface drainage by a cross slope aopte byTresaguest, but obtained it by laying foundation stone of varying sizes on a flatsubgrade.
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In 1827 Jhon Mc Adam, the forerunner of the modern highwayintroduced a completely different method of road constructionbased on scientific observations
1. The earth based or subgrade that the road is built on, ultimately carried the totalload
2. Any well rained compacted good soil could carry such a load. Hence subgradedrainage under a pavement is important
3. Structure stability of the pavement structure
4. Stones on the surface layer should be smaller than the width of the wheel or else loosening of the surface could occur
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Defined by users (drivers) Develop methods to relate physical attributes to driver ratings
Result is usually a numerical scale
From the AASHO Road
Test (1956 – 1961)
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Pavement
Flexible Rigid Composite
Pavements are classified as “ flexible” or “ rigid ” or “ composite” depending on how they distribute surface loads
Constructed using
granular material
and bitumen
Constructed of
Portland cement
concrete (PCC)
Base layer of PCC
and a surface layer
of hot-mix asphalt
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Flexible pavements are those which are surfaced (i.e.,paved) with bituminous materials such as asphalt concrete
Asphalt concrete possess a lower stiffness (EI) thanPortland cement concrete due to lower modulus of
elasticity of asphalt concrete as compared to Portlandcement concrete
Due to lower stiffness of asphalt concrete the totalstructure of a flexible pavement "bends" or "deflects"under traffic loads. This is the logic behind calling such apavement as "flexible pavement”
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Flexible pavements distribute the wheel load over a cone-shaped area under the wheel, reducing the imposed unitstresses as depth increases
Load distribution under a
flexible pavement
Stress at lower depth is
higher than the stress
at higher depth
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Rigid pavements are those which are surfaced (i.e., paved)with Portland cement concrete
Portland cement concrete possess a substantially higher
stiffness (EI) than asphalt concrete due to higher modulus of elasticity of Portland cement concrete as
compared to asphalt concrete
Due to high stiffness of Portland cement concrete the
total structure of a rigid pavement "bends" or "deflects"very little under traffic loads. This is the logic behind
calling such a pavement as “rigid pavement”
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Rigid pavements act as flexural members and distribute the
wheel load fairly uniformly over the area under the pavement
slab
Load distribution under
a rigid pavement
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Structure Surface course
Base course
Subbase course
Subgrade
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Subgrade: Prepared roadbed consisting of natural or
imported soil Subbase course: This is the layer (or layers) under the
base layer. A subbase is not always needed andtherefore may often be omitted .
Base course: This is the layer directly below the
Portland cement concrete layer and generally consistsof aggregate or stabilized subgrade.
Surface course: This is the top layer and the layer thatcomes in contact with traffic. It consists of the
Portland cement concrete slab
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Jointed Plain Concrete Pavement (JPCP)
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Continuously Reinforced Concrete Pavement (CRCP)
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Slip form
Fixed form
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Structure Surface (Wearing) course
Base course
Road-base course
Sub-base course
Subgrade
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Subgrade: Prepared roadbed consisting of natural or importedsoil
Sub-base course: A layer between the subgrade and the road-base course, made from materials superior to that of subgrade.
In case of a good quality of subgrade, the subbase course isomitted.
Road-base course: A layer between the sub-base and the basecourse
Base course: This is the layer directly below the asphaltconcrete layer and generally consists of aggregate (either stabilized or unstabilized).
Surface course: This is the top layer and the layer that comesin contact with traffic. It may be composed of one or severaldifferent asphalt concrete sub layers
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Dense-graded
Open-graded Gap-graded
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The functions of the different layers of flexible pavement are as follows
1. Wearing coursea) Withstands direct traffic loading.
b) Provides smooth riding
c) Provides skid resistant surface
d) Waterproofs the pavement
2. Base-course(a) Supports wearing course
(b) Assists protecting layers below
3. Road-base(a) Main load spreading layer of the pavement structure
4. Sub-basea) Assists load spreading
b) Assists subsoil drainagec) Acts as temporary road for construction traffic
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Granular sub-base, called Type 1 Graded Granular sub-base, called Type 2
(Crushed rock; slag; or other hard material such as smaller size materialother than what specified in Type 1. Therefore, natural sands and gravels.)
Type 1 is stronger
It has good part ic le distr ibut ion and hence good
interlock ing qual ity
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Sieve sizePercentage passing
Type 1 Type 2
75 mm 100 100
37.5 mm 85-100 85-100
10 mm 40-70 45-1005 mm 25-45 25-85
600 μm 8-22 8-45
78 μm 0-10 0-10
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Upper Sub-baseLower Sub-base( Capping layer or
Selected Subgrade)
Flex ib le Rig id Flex ib le
Soil Type Type I & II Type I & II
Liquid Limit (LL) Not to exceed
40%
Not to exceed
25%
Not to exceed 40%
Plasticity Index (PI) Not to exceed
15%
Not to exceed
6% Not to exceed 15%
Maximum Dry Density Not less than 1,750 kg/m3 Not less than 1,650 kg/m3
4-days soaking CBR at
98% MDD Not less than 30% Not less than 15%
Layers thickness Not exceed 225 mmCompaction using 8-10 tonne smooth wheel roller
Optimum moisture content 2 %
Degree of Compaction 98% 95%
Standard Specification for Construction and Maintenance of Roads and Bridges (ICTAD- SCA/5)
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Wet mix macadamCrushed rock graded and mixed with 2-6% water. Laid in 200 mm layers andcompacted or rolled
Dry bound macadam
37.5 mm to 50.0 mm single size crushed rock laid in 75-100 mm thicklayers and rolled
A 25mm thick 4.7mm down crushed rock layer is laid on top and vibratedinto the course layer
Repeat until no more smaller material can be worked in. Excess finesremoved and additional course layers are laid to build the requiredthickness of road-base
Dense bituminous macadam
Crushed rock (fines
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Rolled asphaltWell graded crushed rock (35% fine aggregate and 65% coarseaggregate) plant mixed with 50 – 70 % pen grade bitumen
Lean concrete
Cement bound road-base
Soil cement and cement bound granular road base.Mixtures of soil or granular material and cement, laidfull depth in one layer and rolled.
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Single sized aggregate
base
Water bound &
Dry bound
macadam
bases
Dense graded
aggregate basesPenetration Macadam bases Bitumen bound bases
Material Broken or crushed stonenominal single size 50mm
or 37.5mm and 20mm or
14mm respectively
Broken or crushed
stone nominal
single size 50mm
or 63mm and
crusher fines
Shall be graded
crushed rock nominal
single size 37.5mm or
28mm or 20mm
Coarse aggregate shall be
50mm or 37.5 mm and key
aggregate shall be 20mm or
14mm
Bituminous binder shall be
80-100 penetration grade
bitumen or 10-20 % cutback
bitumen or MC 800 or
MC3000 cutback bitumen or
bitumen emulsion CRS-2
Coarse aggregate shall
be 37.5 mm or 20mm
and fine aggregate shall
conform to general
requirements
Binder shall be 60-70
penetration grade
bitumen
Thickness of
base course
(compacted)
75mm-50mm aggregate
& 20mm choker stone
55mm- 37.5 mm
aggregate & 14mmchoker stone
150mm- 100mm
aggregate, 50mm
aggregate & 20mm
choker stone
130mm- 100mm
aggregate, 37.5mm
aggregate & 14mm
choker stone
Not less than
75mm and shall
not normally
exceed 200mm
Not less than 75mm
and shall not normally
exceed 200mm
75 mm- 50mm aggregate
55mm- 37.5mm aggregate
Max 100mm
Min 60mm
Compactionusing
8-10 tonne steel wheelroller or approved vibratory
rollers
8-10 tonne steelwheel roller or
approved vibratory
rollers
8-10 tonne steel wheelroller or approved
vibratory rollers
8-10 tonne smooth wheel roller
Optimum
moisture content2% 2% 2%
Degree of
CompactionNot less than 98% Not less than 98% Not less than 98% 92%
Standard Specification for Construction and Maintenance of Roads and Bridges (ICTAD- SCA/5)
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Base-course Open textured macadam
Coarse graded, no fines
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Wearing course Bituminous surface dressing and a layer of
chippings
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Wearing course Hot rolled asphalt
The Strongest and durable.
Made of high fines
Laid 40 mm thick with 20 mm coated chippings rolled into the surface
for better skid resistance.
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The strength of the sub-grade - California Bearing Ratio(CBR) is one measure of sub-grade strength
The number of wheel load applications on the
pavement during the design life
An empirical relationship, layer thicknesses havewith CBR value of sub-grade and number of wheel
load applications
Locally available materials for construction
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CBR is a measure of resistance of material topenetration of a plunger under controlled density and
moisture conditions
Most universally acceptedpavement design methods
A standard penetration-type load-deformation test iscarried out, and using the values obtained from thetest from an empirical design chart, the pavementthickness are calculated
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Apparatus
Cylindrical mould
ventilated oven - Thermostatically
controlled to maintain a temperatureof 105 ± 5 °C.
A balance
Test sieves
Loading machine
5000kg (rate
1.25mm/min)Filter paper
Spacer Disc
Surcharge weight
Rammers
Detachable base plate
Slotted weight
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Procedure The specimen is mixed with enough water to dampen it
to achieve the required laboratory moisture ratio. It is
then left to cure for as long as it takes for the water to be
thoroughly mixed into and uniformly distributed
Compact into mould using modified compaction
Load is applied on the sample by a standard plunger
at the rate of 1 ± 0.2 mm/min
Dynamic compaction
L igh t Comp. Heavy Comp.
No. of layers 3 5
Rammer weight 2.6 kg 4.89 kg
Fall 31 cm 45 cm
Blows/layer 56 56
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Results
Plot the load penetration curve
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y
xCBR 100
Results
x = material resistance or the unit load on
the piston (pressure) for 2.5 mm or 5
mm of penetration
y = standard unit load (pressure) for well
graded crushed stone.For 2.5 mm of penetration = 13.2 kN
For 5.0 mm of penetration = 19.5 kN
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Results
Read the force value in N at penetrations of 2.5mm and
5.0mm and calculate the bearing ratio for each by
dividing by 13.2kN and 19.5kN respectively, then
multiplying by 100
The greatest value calculated for penetrations at 2.5mm
and 5.0mm will be recorded as the CBR
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2.5
5.0
New origin
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California Bearing
Ratio Equipment
California Bearing Ratio Vs
Moisture content
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General Soil Type USC Soil Type CBR Range
Clean gravelsGW 40 – 80
GP 30 – 60
Gravels with finesGM 20 – 60
GC 20 – 40
Clean sandsSW 20 – 40
SP 10 – 40
Sands with finesSM 10 – 40
SC 5 – 20
Silts and clays
ML 15 or lessCL 15 or less
OL 5 or less
MH 10 or less
CH (LL>50%) 15 or less
OH 5 or less
USC-Unified Soil Classification
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The flow chart leading to the design
of flexible pavement using steps
discussed in road note 31
Overseas Road Note 31
“A guide to the structural design of
bitumen-surfaced roads in tropical and
sub tropical countries” published by
Transport Research Laboratory (TRL),
United Kingdom gives a simple but
adequate design procedure for most
Sri Lankan roads
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Several typical methods
CBR Method
Asphalt Institute method
California Method
AASHTO Method
Mechanistic design Method
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KEY TO STRUCTUREAL CATALOGUE
Traffic Classes Sub-grade strength classes
Traffic class 106 esa Range Sub-grade strength class Range of CBR %
T1 < 0.3 S1 2
T2 0.3 - 0.7 S2 3 – 4
T3 0.7 - 1.5 S3 5 -7
T4 1.5 - 3.0 S4 8 – 14
T5 3.0 – 6.0 S5 15 – 29
T6 6.0 – 10 S6 30 +
T7 10 – 17
T8 17 - 30 49
In this method, the CBR values are used to determine the
total thickness of the flexible pavement and its various layers
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Wheel load applicationsThe required data for pavement design
CBR value
The number of times wheel loads are applied to the pavement
This is based on the design life, the anticipated number of differenttypes of vehicles using the pavement during the design life and theequ ivalen t fac to rs (EF) for each vehicle type which converts anaxle loading to a standard axle loading
=
.
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0.0007 0.10
1.35 1.85
5.11
0
1
2
3
4
5
6
Car Delivery Truck Loaded 18-Wheeler
Loaded 40' Bus Loaded 60'Articulated Bus
E F
p e r V e h i c l e
51
=
.
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Equivalent standard axles (esa) Base year traffic flow is the Annual Average Daily Traffic
(AADT) of the base year
The number of vehicles is converted into equivalent standardaxles (esa)
= × ×
Use growth factor (r) for each vehicle class and the assigned designlife (n years) to calculate cumulative esa
= × + −
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Directional factor (f D)
Directional Distribution Directional factor f D
50/50 1.00
60/40 0.94
70/30 0.89
80/20 0.83
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KEY TO STRUCTUREAL CATALOGUE
Traffic Classes Sub-grade strength classes
Traffic class 106 esa Range Sub-grade strength class Range of CBR %
T1 < 0.3 S1 2
T2 0.3 - 0.7 S2 3 – 4
T3 0.7 - 1.5 S3 5 -7
T4 1.5 - 3.0 S4 8 – 14
T5 3.0 – 6.0 S5 15 – 29
T6 6.0 – 10 S6 30 +T7 10 – 17
T8 17 - 30
56
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According to road note 31Shows the flow chart leading to the design of flexible using stepsdiscussed in road note 31
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T1 T2 T3 T4 T5 T6 T7
S1
S2
S3
S4
S5
S6
150
SD
175
300
150
SD
225*
300
200
SD
200
300
200
SD
250*
300
200
SD
300
300*
225
SD
300
325*
150
SD
150
200
150
SD
200
200
200
SD
175
200
200
SD
225*
200
200
SD
275*
200
225
SD
300*
200
SD
150
200
SD
150
250
SD
200
225
SD
200
275*
SD
200
325*
SD
225
350*
SD
150
125
SD
225
275
SD
150
175
SD
200
150
SD
200
200
SD
200
250
SD
250
175
SD
150
100
SD
150
100
SD
175
100
SD
200
125
SD
225
150
SD
250SD
150
SD
150
SD
175
SD
200
SD
225
GRANULAR ROADBASE /
SURFACE DRESSING
Notes
1. Up to 100mm of sub-base
may be substituted with
selected fill provided the sub-
base is not reduced to les
than the road-base thickness
or 200mm whichever is the
greater. The substitution ratio
of sub-base to selected fill is25mm-32mm.
2. A cement or lime stabilized
sub-base may also be used.
shows the legend of description of pavement materials necessary to refer
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COMPOSITE ROADBASE
(UNBOUND AND CEMENTED)
/ SURFACE DRESSING
Notes
1. Sub-base to fill substitution
not permitted.
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GRANULAR ROADBASE /
SEMI-STRUCTURAL
SURFACE
Notes
1. * Up to 100mm of sub-base
may be substituted with
selected fill provided the sub-
base is not reduced to les
than the road-base thickness
or 200mm whichever is the
greater. The substitution ratio
of sub-base to selected fill is25mm-32mm.
2. A cement or lime stabilized
sub-base may also be used.
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COMPOSITE ROADBASE /SEMI-STRUCTURAL
SURFACE
Notes
1. Sub-base to fill substitution
not permitted
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GRANULAR ROADBASE /STRUCTURAL SURFACE
Notes
1. * Up to 100mm of sub-base
may be substituted with
selected fill provided the sub-
base is not reduced to les
than the road-base thickness
or 200mm whichever is the
greater. The substitution ratio
of sub-base to selected fill is25mm-32mm.
2. A cement or lime stabilized
sub-base may also be used.
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COMPOSITE ROADBASE /STRUCTURAL SURFACE
Notes
1. Sub-base to fill substitution
not permitted.
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BITUMINOUS ROADBASE /SEMI-STRUCTURAL
SURFACE
Notes
1. * Up to 100mm of sub-base
may be substituted with
selected fill provided the sub-
base is not reduced to less
than the road-base thickness
or 200mm whichever is the
greater. The substitution ratio
of sub-base to selected fill is25mm-32mm.
2. A cement or lime stabilized
sub-base may also be used.
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BITUMINOUS ROADBASE /SEMI-STRUCTURAL
SURFACE
Notes
1. A granular sub-base may
also be used.
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Road note 31
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Road note 31
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68
Road note 31
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Road note 31
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Road note 31
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Example: Design a flexible for the AADT values given in the table and a soil with CBR 6.5.
Step1:Base Year Equivalent Standard Axles ( )
Axle load of
vehicle class (KN)
AADT of vehicle
class
Equivalent Factor
(EF)
3.0 450 0.01 16434.0 380 0.04 5548
5.0 250 0.11 10038
6.0 100 0.25 9125
7.0 85 0.50 15513
8.0 75 0.91 24911
9.0 40 1.55 2263010.0 35 2.50 31938
11.0 25 3.83 34949
12.0 15 5.67 31043
= × ×
=
.
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Step2: Calculation of cumulative esa
Axle load of
vehicle classBase year esa
Growth
Factor
(%)
Design
life (n
years)
Cumulative esa
()
3.0 1643 4 10 197264.0 5548 3 10 63602
5.0 10038 3 10 115074
6.0 9125 4 10 109556
7.0 15513 5 10 195121
8.0 24911 5 10 3133289.0 22630 3 10 259428
10.0 31938 4 10 383451
11.0 34949 4 10 419601
12.0 31043 5 10 390456
Total 2269343
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Step 3: Find the traffic & sub grade strength class1. The traffic class is T4
2. Sub grade strength class is S3
Step 4: Refer the charts:
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GRANULAR ROADBASE /SEMI-STRUCTURAL
SURFACE
Notes
1. * Up to 100mm of sub-base
may be substituted with
selected fill provided the sub-
base is not reduced to les
than the road-base thickness
or 200mm whichever is the
greater. The substitution ratio
of sub-base to selected fill is
25mm-32mm.
2. A cement or lime stabilized
sub-base may also be used.
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COMPOSITE ROADBASE /SEMI-STRUCTURAL
SURFACE
Notes
1. Sub-base to fill substitution
not permitted
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BITUMINOUS ROADBASE /SEMI-STRUCTURAL
SURFACE
Notes
1. * Up to 100mm of sub-base
may be substituted with
selected fill provided the sub-
base is not reduced to less
than the road-base thickness
or 200mm whichever is the
greater. The substitution ratio
of sub-base to selected fill is
25mm-32mm.
2. A cement or lime stabilized
sub-base may also be used.
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Notes
1. * Up to 100mm of sub-base may be substituted with selected fill provided the sub-base is not reduced to less
than the road-base thickness or 200mm whichever is the greater. The substitution ratio of sub-base to selected
fill is 25mm-32mm.
2. A cement or lime stabilized sub-base may also be used.
Type Structure
Granular road-base /
semi-structural surfaceNotes
Composite road-base/ semi-structural
surface
Bituminous road-base
/ semi-structural
surfaceNotes
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Road base thickness = 175 mmMinimum Sub base thickness = 175 mm or 200mm whichever is the grater = 200 mm
Substituted layer thickness ( capping layer)
= 325mm – 200 mm
= 125 mm (but maximum capping layer thickness is 100mm)
= 100 mm
New sub base thickness =325 mm – 100 mm = 225 mm
Actual thickness of capping layer
= 100/25 X 32 (The substitution ratio of sub-base to selected
fill is 25mm-32mm)
= 128 mm
How to do the economical design
Notes
1. * Up to 100mm of sub-base may be substituted with selected fill provided the
sub-base is not reduced to less than the road-base thickness or 200mm
whichever is the greater. The substitution ratio of sub-base to selected fill is
25mm-32mm.
2. A cement or lime stabilized sub-base may also be used.
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The section of economical design
225
128
Normal design Economical design
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Upper Sub-baseLower Sub-base
( Capping layer or Selected
Subgrade)
Liquid Limit (LL) Not to exceed 40% Not to exceed 40%
Plasticity Index (PI) Not to exceed 15% Not to exceed 15%
Maximum Dry Density
Not less than 1,750
kg/m3 Not less than 1,650 kg/m3
4-days soaking CBR at 98%
MDD Not less than 30% Not less than 15%
Layers thickness Not exceed 225 mm
Compaction using 8-10 tonne smooth wheel roller
Optimum moisture content 2 %
Degree of Compaction 98% 95%
Standard Specification for Construction and Maintenance of Roads and Bridges (ICTAD- SCA/5)