highway engineering design_pavement design

8/16/2019 Highway Engineering Design_Pavement Design

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Dr. Wasala Bandara

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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%



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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











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COMPOSITE ROADBASE /SEMI-STRUCTURAL

SURFACE

Notes


not permitted


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GRANULAR ROADBASE /STRUCTURAL SURFACE

Notes












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COMPOSITE ROADBASE /STRUCTURAL SURFACE

Notes


not permitted.


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BITUMINOUS ROADBASE /SEMI-STRUCTURAL

SURFACE

Notes




base is not reduced to less








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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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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








of sub-base to selected fill is

25mm-32mm.




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COMPOSITE ROADBASE /SEMI-STRUCTURAL

SURFACE

Notes


not permitted


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SURFACE

Notes




base is not reduced to less




of sub-base to selected fill is

25mm-32mm.




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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%


highway engineering design_pavement design

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