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Design of flexible pavement for widening : A Case Study of SH-8 stretch from Tarapur 0/000 km

to Vasad 48/300 km

BVM Engineering College Page 9

Gujarat Technological University

2. Literature Review

2.1 STUDY OF FLEXIBLE PAVEMENTS FOR DIFFERENT SOIL

AND TRAFFIC CONDITIONS

The two most important factors that govern pavement design are soil sub-grade

strength and traffic loading. Depending on the strength of sub-grade soil, the layer

thickness of flexible are affected. IRC:37-2001 uses soil sub-grade strength in terms

of CBR.

The accurate determination of axle load spectra is crucial in the effective design as

well as damage investigation of pavements. The Motor Vehicles Act, 1988 stipulates

axle load limits for the different axle configurations (that is single, tandem, and multi

axles). However, these limits are seldom followed in actual practice as per the

prevailing regulatory system and consequently a large number of commercial vehicles

are overloaded.[1]

2.2 PERCENT DESIGN ACTIVITIES[2]

New Pavement:

Pavement structure prepared on sub-grade. It applies to new highway construction, to

a relocated highway, or to the new part of a widened highway.

Pavement Reconstruction:

Reconstructed pavement or full depth reconstruction result when an existing

pavement structure is completely removed to the sub-grade and replaced with a new

pavement structure. This type of work is needed when the existing pavement has

deteriorated to such a weakened condition that it cannot be salvaged with corrective




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action. The type and extent of a pavement distress will determine when pavement

reconstruction is necessary.[2]

Pavement Reclamation:

Reclaimed pavement reuses an existing pavement structure through the pulverizing

and mixing of the existing pavement and granular sub-base into a gravel base material

to be overlaid with new HMA[22] layers. The reclamation method is usually performed

on site.

Pavement Resurfacing:

Pavement resurfacing consists of placing the needed thickness of hot mix asphalt on

existing pavement. The resurfacing will return the pavement to a high level of

serviceability and provide the necessary structural strength for the pavement design

period.

Pavement Preservation:

Pavement Preservation involves the application of properly timed surface treatments

to ensure that pavements in good condition will remain in good condition.

Preservation treatments extend the pavement service life, but generally provide no

structural strength.[2]

2.3 PREAMBLE

The Government Roads comprise of National Highways (NH), State

Highways (SH), Major District Road (MDR), Other District Roads (ODR), andCross Drainage Works like bridges, Causeways, Culverts, Road Over Bridge (ROB)

and Road Under Bridge (RUB).[10]

NH: Main highways running through the length and breadth of the

Country connecting major ports, State Capitals, large industrial and

tourist center.

SH: Arterial routes of a State linking District Headquarters and

important cities within the State and connecting them with NH or




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Highways of the neighboring States.

MDR: Important roads within a district serving areas of production and

markets and connecting those with each other or with main highways

ODR : Roads serving rural areas of production and providing them with

outlet to market centers, taluka headquarters, Block Development

headquarters or other main roads.

Table 2.1 Category wise Road Length[10]

Road Classification Total Road Length (Km)

National Highways70,934 + 40,000 Km under

implementation

State Highways 1,54,522

Major and other District Roads 25,77,396

Rural and other Roads 14,33,577

Total Road Length 42,36,429 Km

Source: Annual Report 2010-11, Ministry of Road Transport and Highways,Government of India




to Vasad 48/300 km



Fig. 2.1 Road Network in India

The roads are again grouped as Single lane (3.5 m), intermediate lane (5.5 m), Double

lane (7m with kerb or 7.5 m without kerb) and multiple lanes (addl. 3.5 m for

each lane) depending upon the width of Carriageway. On village roads, the width

may be restricted to 3 m. Roads are broadly classified as Rural Roads and Urban

Roads.

Expressways0.02%

National

Highways1.67%

State Highways

3.65%

Major and other

District Roads

60.82%

Rural and other

Roads

33.83%

Road Network in India




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Table 2.2 Rural Road Network in India, tends over 10 years*

Kilometers in

2001

Kilometers as

of May 2011

Kilometers

under

constructionin 2011

Total Rural Roads 2.7 million 3.1 million 0.1 million

Paved, not maintained

Rural Roads0.5 million

Unpaved Rural Roads 2.2 million 1.9 million

Paved, maintained RuralRoads

7,28,871 53,634

New Rural Roads 3,22,900 82,734

*Source: Annual Report 2010-11, Ministry of Road Transport and Highways, Government

of India

2.4 PARAMETER OF DESIGN FRAMEWORK

2.4.1 TRAFFIC PARAMETER [15]

The traffic in terms of the cumulative number of Standard axles (8160 Kg) to

be carried by the pavement during the design life. The following information is

needed:

i) Initial traffic after construction in terms of number of

commercial vehicles per day (CVPD)

ii) Traffic growth rate during the design life in percentage

iii) Design life in number of years

iv) Vehicle damage factor (VDF)

v) Distribution of Commercial traffic over the carriageway.

a) Initial Traffic : Estimate of initial daily average traffic flow for any road

should normally be based on at least 7 days, 24 hour classified traffic counts.




to Vasad 48/300 km



In case of new roads, traffic estimates can be made on the basis of potential

land use and traffic on existing routes in the area.

b) Traffic growth rate: Traffic growth rates should be estimated by study.

If adequate data is not available, average annual growth rate of 7.5%

may be adopted. The factor is reduced to 6% for roads designed adopting

IRC:SP 20-2002

c) Design life : The Design life is defined in terms of cumulative

number of Standard axles that can be carried before strengthening of

the pavement. Normally the pavement for NH & SH is the designed

for life of 15 years, Expressways and Urban roads for 20 years and other

roads for 10 to 15 years. When it is not possible to provide the full

thickness of pavement at the time of initial construction, stage construction

technique should be resorted to. Roads in Rural areas should be designed

for a design life of 10 years.[11]

d) Vehicle damage factory(VDF):VDF is arrived at from axle load surveys.

The indicative value of VDF factor is given below:

Use Vehicle Damage Factor (VDF) in estimation of cumulative msa for

thickness design of pavements. The Vehicle Damage Factor (VDF) is a

multiplier to convert the number of commercial vehicles of different axle

loads and axle configuration into the number of repetitions of standard axle

load of magnitude 80 kN. It is defined as equivalent number of standard axles

per commercial vehicle. The VDF varies with the vehicle axle configuration

and axle loading.

The equations for computing equivalency factors for single, tandem and

tridem axles given below should be used for converting different axle load

repetitions into equivalent standard axle load repetitions. Since the VDF

values in AASHO Road Test for Flexible and Rigid pavement are not much

different, for heavy duty pavements, the computed VDF values are assumed

to be same for bituminous pavements with cemented and granular base.[5]

VDF should be arrived at carefully by carrying out specific axle load surveys

on the existing roads. Minimum sample size for survey is given in Table 2.3.




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Table 2.3 Sample size for Axle Load Survey[15]

Total number of

Commercial Vehicles perday

Minimum percentage

of Commercial Traffic to besurveyed

<3000 20 per cent

3000 to 6000 15 per cent

>6000 10 per cent

Axle load survey should be carried out without any bias for loaded or unloadedvehicles. On some sections, there may be significant difference in axle loading in

two directions of traffic. In such situations, the VDF should be evaluated

direction wise. Each direction can have different pavement thickness for divided

highways depending upon the loading pattern.[15]

( )

⁴

( )

⁴

( )

⁴

( )

⁴




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Table 2.4 Indicative Vehicle Damage Factor values[15]

Initial Traffic in terms of commercial

vehicle per day

Terrain

Rolling/Plain Hilly

0-150 1.5 0.5

150-1500 3.5 1.5

More than 1500 4.5 2.5

Distribution of Commercial traffic over the carriage way:[15]

i) Single lane : Design should be based on total number of commercial vehicle in both

directions multiplied by two

ii) Two lane (single Carriageway): 75% of the total number of commercial vehicle

in both the direction.

iii) Four lane (single Carriage way) : 40% of the total number of commercial

vehicle in both the direction.

iv) Dual Carriageway: 75% of the number of commercial vehicle in each direction.

For dual 3 lane and dual 4 lane carriageway, the distribution factor will be

60% and 45% respectively.[15]

Computation of design traffic under IRC 37: 2012

The design traffic is considered in terms of Cumulative number of standard axles

to be carried during the design life of the road. Computed by the equation




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Where,

N: The cumulative number of standard axles to be catered for in the design in

terms of MSA

A: Initial traffic in the year of completion of construction in terms of number of

commercial vehicles per day

D: Lane distribution factor

F: Vehicle Damage Factor

n: Design life in years

r: Annual growth rate of commercial vehicles (for 7.5% annual growth rate

r=0.075)

The traffic in the year of completion is estimated using the following formula:

A= P

Where P = Number of Commercial vehicle as per last count

X = Number of years between the last count and the year of completion

of construction

2.4.2 SOIL PARAMETER:

One of the main parameter designing pavement is the quality of soil in the

roadway. For design purpose, top 500 mm portion of the roadway/embankment

if formed with filling materials, immediately supporting the pavement, termed as

sub grade, is considered for design purposes. Whereas in rural road the top 30

cum of cutting or embankment at the formation level is considered as sub grade.

Embankment construction[14]

:

1) The stability of an embankment depends upon the foundation, the use of

suitable materials, proper placing and compacting of the materials and strict

adherence to quality control measures. The suitability of embankment material is

shown in Table 2.5 and Table 2.6 indicates the compaction requirements.




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2) After cleaning and grubbing, the sub grade level should be compacted at least

97 % Proctor Density of determined laboratory Proctor Density as per IS-2720

(Part VIII).

3) Clods or hard lumps of earth should be broke down and embankment and sub

grade material should be spread in layer of uniform thickness not exceeding 200

mm compacted thickness over entire width.

Table 2.5 Suitability of embankment materials[14]

S. No. Type of Work

Maximum laboratory dry unit

weight when tested as per IS: 2720(Part VIII)

1. Embankment upto 3 mts. height, not

subjected to extensive flooding Not less than 15.2 kN/cu.m

2. Embankment exceeding 3 mts. height or

embankment of any height subject to

long periods of inundations

Not less than 17.5 kN/cu.m

3. Sub grade and earthen shoulders /verges

/backfill Not less than 17.5 kN/cu.m

Table 2.6 Compaction requirement for embankment and sub grade[14]

S. No. Type of Work Relative compaction as percentage

of maximum laboratory dry

density as per IS:2720 (Part VIII) 1. Sub grade and earthen shoulders Not less than 97

2. Embankment Not less than 95

3. Expansive Clays

a) Sub grade and 500 mm portion just below the sub grade

Not allowed

b) Remaining portion of

embankment Not less than 90

Embankment under special conditions:[21]

Widening existing embankment or construction against sloping ground

1) End dumping of materials from trucks on widened portions should be

avoided as far as possible.




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2) If existing side slopes are steeper than 4: 1, cut horizontal benches 0.3

m wide to ensure bond. If the slopes are 4:1 or flatter, the surface

may be roughened by ploughing or scarifying.

3) For wet conditions benches with slightly inward fall and sub-soil drains at

the lowest point shall be provided before the fill is placed against slopping

ground.

Earthwork over existing road surface:

If within 1m of the new sub grade level, scarify to a depth of 50 mm or

more if specified, if the road surface is BT, and completely removed, if of

cement concrete. If the level difference is more than one m, allow the

existing road surface to stay.

Embankment around structures:

Suspend filling around structures upto a distance of twice the height

of the embankment. Permit filling only after the concrete/masonry has

been in position for at least 14 days. Bring up the embankment in equal

horizontal layers simultaneously on each side to avoid undue thrust and

unequal pressure.

The material used for backfill should not be an organic soil or highly

plastic clay, plasticity index and liquid limit should not be greater than 20

and 40 respectively.

Embankment construction under water:

Only acceptable granular material or rock should be used for filing-under

water. The material should consist of graded hard durable particles of size

not exceeding 75 mm. This material should be non-plastic having

uniformity co-efficient of not less than 10.

Earthwork high embankment:

Earthwork for high embankment should be carried out by stage

construction of fills at controlled rates of filling. The embankment should

be surcharged for the specified period.

At the stage of formation level, surcharge where used material should be

removed. High embankment should remain in place for the required

settlement period before excavating footings for structures, like, abutment

wing wall, etc.




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A. Sub grade:

Sub grade is normally formed with natural earth

Compacted to 97% of dry density IS 2720 (Part 8)

Materials used for sub grade construction should have the dry density of

not less than 1.75 gm/cc

Wherever necessary, the original ground shall be leveled to

facilitate placement of first layer of embankment, scarified, mixed with

water and then compacted by rolling so as to achieve minimum dry

density. In case where the difference between the subgrade level and the

ground level is less than 0.5m (0.3 m for Rural Roads) below the

subgrade level watered and compacted in layers to achieve not less than

97% dry density (clause 305.3.3 of MORTH)

When the soil does not fulfill the requirements of normal subgrade soil, a

stabilization technique can be used to modify and improve the same.

Stabilization is of different type viz., stabilization with lime, sand,

cement, coal ash, soft aggregates, gravel/moorum and mechanical

stabilization etc., As far as possible a non expansive soil should not be

used for the sub grade

The sub grade strength is assessed in terms of the CBR (California

Bearing Ratio)

The design should be based on the CBR value of the weakest soil

type proposed to be used for subgrade construction or encountered

extensively at subgrade level over a given section of the road.

Pavement thickness on new road may be modified at intervals (say 1 Km)

based on the CBR values.

Where the variation in CBR test is + or – 1 and + or – 2 for soil sample

having CBR value less than 5% and 5-10% respectively then the CBR

value should be the average of test from at least 6 samples.

Where CBR value of sub grade is less than 2% a capping layer of 150

mm thickness of materials with a minimum CBR of 10% shall be

provided in addition to the sub base. (normally sand would be used)

Where embankment was formed, the CBR value of sub grade has to be

tested and pavement design modified, if necessary.




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B. Sub base:

Material comprise natural sand, moorum, gravel, metal, laterite crushed

stone etc.

Should have liquid limit and plasticity index of not more than 25 and 6

respectively

Should have CBR value minimum of 20% for cumulative traffic upto 2

msa and 30% exceeding 2 msa.

Where stage construction is adopted for pavements, the thickness of

subbase shall be provided for ultimate pavement section for the full

design life.

for drainage consideration the granular sub base should be extended over

entire formation width in case of the sub grade soil is of relatively low

permeability. The thickness of sub base in the extended portion should

not be less than 150 mm for traffic less than 10 msa and 200 mm for

design traffic of 10 msa & above.[21]

C. Base course:

Granular base comprises water bound macadam (WBM), wet mix

macadam

(WMM) or other equivalent granular construction[17]

minimum 225 mm thickness for traffic upto 2 msa and 250 mm for traffic

exceeding 2 msa

where road carrying traffic more than 10 msa, the thickness of WBM base

shall be increased from 250 mm to 300 mm (i.e. 4 layers of WBM grade

II and III each of 75 mm compacted thickness) with corresponding

reduction in the sub base thickness keeping the over pavement thickness

unchanged

for heavy traffic road use WMM

WBM in layers of 75 mm thick of grade II & III used[13]

Built up spray grout (BUSG) shall also be used for base in a single course

in pavement.




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D. Bituminous Surfacing:

Comprise of either a wearing course or a binder course with wearing

course depending on traffic intensity and structural requirements

Wearing course — open grade premix carpet, surface dressing, semi

dense bituminous carpet (SDBC), Bituminous Concrete (BC)

Binder course – Bituminous Macadam (BM), Dense Bituminous

Macadam(DBM)

DBM is recommended for road designed to carry more than 5 msa

DBM binder course may be preceded by a 75 mm thick BM layer. when

this is done, the thickness of DBM layer will be suitably reduced. 10mm

BM can be taken as equivalent to 7 mm DBM[22]

DBM shall be constructed in two layers when it is more than 100 mm

Mastic asphalt maybe used at bus-stops and intersections.

Where Wearing course of open graded premix carpet of thickness upto

25mm, should not be counted towards the total thickness of the pavement.




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2.4 SEQUENCE OF ACTIVITIES AT SITE :

Fig. 2.2 Chronology of Activities at site

Survey of site

and soil

investigation

Design of

elements (Road

structure)

Clearing and

Grubbing

Excavation

Soil

Embankment

Tack Coat

DBM

Traffic

diversion

ECW

Traffic

diversion

Prime Coat

Kerb

WMM

Granular sub-

base

Sub grade

BC

Tack Coat

Cleaning

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