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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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Design of flexible pavement for widening : A Case Study of SH-8 stretch from Tarapur 0/000 km
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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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Design of flexible pavement for widening : A Case Study of SH-8 stretch from Tarapur 0/000 km
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Gujarat Technological University
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
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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
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Gujarat Technological University
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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Design of flexible pavement for widening : A Case Study of SH-8 stretch from Tarapur 0/000 km
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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.
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Design of flexible pavement for widening : A Case Study of SH-8 stretch from Tarapur 0/000 km
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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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Design of flexible pavement for widening : A Case Study of SH-8 stretch from Tarapur 0/000 km
to Vasad 48/300 km
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Gujarat Technological University
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]
( )
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Design of flexible pavement for widening : A Case Study of SH-8 stretch from Tarapur 0/000 km
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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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Design of flexible pavement for widening : A Case Study of SH-8 stretch from Tarapur 0/000 km
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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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Design of flexible pavement for widening : A Case Study of SH-8 stretch from Tarapur 0/000 km
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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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Design of flexible pavement for widening : A Case Study of SH-8 stretch from Tarapur 0/000 km
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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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Design of flexible pavement for widening : A Case Study of SH-8 stretch from Tarapur 0/000 km
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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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Design of flexible pavement for widening : A Case Study of SH-8 stretch from Tarapur 0/000 km
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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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Design of flexible pavement for widening : A Case Study of SH-8 stretch from Tarapur 0/000 km
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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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Design of flexible pavement for widening : A Case Study of SH-8 stretch from Tarapur 0/000 km
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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