flexible pavement presentation
TRANSCRIPT
FLEXIBLE PAVEMENTTHEORY AND DESIGN
Guide : Dr. Shashikant Sharma, Assistant prof. Civil engineering department.
NATIONAL INSTITUTE OF TECHNOLOGY, HAMIRPURDEPT. OF CIVIL ENGINEERING, 2016
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THEORY OF FLEXIBLE PAVEMENT :
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Presented by: Md. Taiyab Jawed (16M144) Pawan Kumar (16M145) Gyandeep Singh Arya (16M146)
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What is pavement ?
A structure consisting of superimposed layers of processed materials above the natural soil sub-grade, whose primary function is to distribute the applied vehicle loads to the sub-grade.
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Types of Pavement
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PAVEMENT
FLEXIBLE PAVEMENT RIGID PAVEMENT
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Flexible pavement:
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Flexible pavements are those which on a whole have low or negligible flexural strength and rather flexible in their structural action under load.
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Load transfer:
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Load is transferred to the lower layer by grain to grain distribution as shown in the figure given below;
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Load Transfer (continue …)
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The wheel load acting on the pavement will be distributed to a wider area, and the stress decreases with the depth. Flexible pavement layers reflect the deformation of the lower layers on to the surface layer
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TYPICAL LAYERS OF A FLEXIBLE PAVEMENT :
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Typical layers of a conventional flexible pavement includes seal coat, surface course, tack coat, binder course, prime coat, base course, sub-base course, compacted sub-grade, and natural sub-grade.
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TYPICAL LAYERS OF A FLEXIBLE PAVEMENT
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Seal coat is a thin surface treatment used to water-proof the surface and to provide skid resistance.
Tack coat is a very light application of asphalt emulsion diluted with water. And It provides bonding between two layers of binder course.
Prime coat is an application of low viscous cutback bitumen to an absorbent surface like granular bases on which binder layer is placed and provides bonding between two layers.
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TYPICAL LAYERS OF A FLEXIBLE PAVEMENT (Continue ….)
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Surface course is the layer directly in contact with traffic loads and are constructed with dense graded asphalt concrete.
Binder course purpose is to distribute load to the base course. Binder course requires lesser quality of mix as compared to course above it.
Base course provides additional load distribution and contributes to the sub-surface drainage
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TYPICAL LAYERS OF A FLEXIBLE PAVEMENT (Continue ….)
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Sub-base course the primary functions are to provide structural support, improve drainage, and reduce the intrusion of fines from the sub-grade in the pavement structure
Sub-grade The top soil or sub-grade is a layer of natural soil prepared to receive the stresses from the layers above
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FACTORS AFFECTING PAVEMENT DESIGN
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1. Design Wheel Load Max. Wheel load Axle configuration Contact pressure ESWL. Repetition of loads
2. Climatic Factor 3. Pavement component material
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Design Wheel Load.
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Max. Wheel load - It is used to determine the depth of the pavement required to ensure that the subgrade soil does not fail.
Contact pressure - It determines the contact area and the contact pressure between the wheel and the pavement surface. For simplicity elliptical contact area is consider to be circular.
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Design Wheel Load (Continue)
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Axle configuration - the axle configuration is important to know the way in which the load is applied on the pavement surface.
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Design Wheel Load (Continue)
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Equivalent single wheel load (ESWL)
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Design Wheel Load (Continue)
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Repetition of loads :
Each load application causes some deformation and the total deformation is the summation of all these.
Although the pavement deformation due to single axle load is very small, the cumulative effect of number of load repetition is significant.
Therefore, modern design is based on total number of standard axle load (usually 80 KN single axle)
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Climatic Factor
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1. Temperature - Wide temperature variations may cause damaging
effects. Pavement becomes soft in hot weather and brittle
in very cold weather.
2. Variation in moisture condition – It depends on type of the pavement, type of soil
type, ground water variation etc. It can be controlled by providing suitable surface
and sub-surface drainage.
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Characteristic of Pavement material
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1. California bearing ratio- It determines the strength of soil sub-grade, sub-base or base and it is used for the design of pavement.
2. Elastic modulus -It measures the materials resistance to being deformed elastically upon application of the wheel load.
3. Poisson Ratio – It is the ratio of lateral strain to the axial strain caused by a load parallel axis along axial strain.
4. Resilient modulus- The elastic modulus based on the recoverable strain under repeated loads is called the resilient modulus MR =σd/σr .
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Characteristic of Pavement material (Continue ….)
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The following material properties are consider for both flexible and rigid pavements. When pavements are considered as linear elastic,
the elastic moduli and poisson ratio are specified.
If the elastic modulus of a material varies with the time of loading, then the resilient modulus is selected.
Design procedures for flexible pavements:
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Design Procedures
Empirical Design
Mechanistic-Empirical Design
Mechanistic Design
IRC:37-2012 is based on Mechanistic-Empirical Design
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Mechanistic-empirical design
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1. It can be used for both existing pavement rehabilitation and new pavement construction
2. It can accommodate changing load types 3. It uses material proportion that relates
better with actual pavement performance 4. It provides more reliable performance
predictions
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Failures of flexible pavements:
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Different types of failure encountered in flexible pavements are as follow. 1. Alligator cracking or Map cracking (Fatigue) 2. Consolidation of pavement layers (Rutting) 3. Shear failure cracking 4. Longitudinal cracking 5. Frost heaving 6. Lack of binding to the lower course 7. Reflection cracking 8. Formation of waves and corrugation 9. Bleeding 10. Pumping
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1. ALLIGATOR OR MAP CRACKING (FATIGUE CRACKING)
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Followings are the primary causes of this type of failure.
Relative movement of pavement layer material
Repeated application of heavy wheel loads
Swelling or shrinkage of subgrade or other layers due to moisture variation
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2. CONSOLIDATION OF PAVEMENT LAYERS (RUTTING)
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Formation of ruts falls in this type of failure.
A rut is a depression or groove worn into a road by the travel of wheels.
This type of failure is caused due to following reasons.
• Repeated application of load along the same wheel path resulting longitudinal ruts.
• Wearing of the surface course along the wheel path resulting shallow ruts.
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3. SHEAR FAILURE CRACKING:
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Shear failure causes upheaval of pavement material by forming a fracture or cracking.
Followings are the primary causes of shear failure cracking. • Excessive wheel
loading • Low shearing
resistance of pavement mixture
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4. LONGITUDINAL CRACKING:
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This types of cracks extents to the full thickness of pavement.
The following are the primary causes of longitudinal cracking. Differential volume changes in
subgrade soil Settlement of fill materials Sliding of side slopes
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5. FROST HEAVING:
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Frost heaving causes upheaval of localized portion of a pavement. The extent of frost heaving depends upon the ground water table and climatic condition.
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6. LACK OF BINDING WITH LOWER LAYER (POTHOLES & SLIPPAGE)
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When there is lack of binding between surface course and underlying layer, some portion of surface course looses up materials creating patches and potholes.
Slippage cracking is one form of this type of failure.
Lack of prime coat or tack coat in between two layers is the primary reason behind this type of failure.
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7. REFLECTION CRACKING:
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This type of failure occurs, when bituminous surface course is laid over the existing cement concrete pavement with some cracks. This crack is reflected in the same pattern on bituminous surface.
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8. FORMATION OF WAVES & CORRUGATION :
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Transverse undulations appear at regular intervals due to the unstable surface course caused by stop-and-go traffic.
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9. BLEEDING:
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Excess bituminous binder occurring on the pavement surface causes bleeding. Bleeding causes a shiny, glass-like, reflective surface that may be tacky to the touch. Usually found in the wheel paths.
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10. PUMPING:
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Seeping or ejection of water and fines from beneath the pavement through cracks is called pumping
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FAILURES OF FLEXIBLE PAVEMENTS DESIGN CONSIDERATION:
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The design of flexible pavement as per IRC is based on two major failure that are, fatigue cracking and rutting failure.
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IRC METHOD OF DESIGN OF FLEXIBLE PAVEMENTS (IRC: 37-2012)
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1. IRC:37-1970 based on California Bearing Ratio (CBR) of subgrade Traffic in terms of commercial vehicles (more than 3
tonnes laden weight) 2. IRC:37-1984
based on California Bearing Ratio (CBR) of subgrade Design traffic was considered in terms of
cumulative number of equivalent standard axle load of 80 kN in millions of standard axles (msa)
Design charts were provided for traffic up to 30 msa using an empirical approach.
.
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Continue ….
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3. IRC:37-2001 based on Mechanistic-Empirical method Pavements were required to be designed for traffic
as high as 150 msa. The limiting rutting is recommended as 20 mm in
20 per cent of the length for design traffic 4. IRC:37-2012
based on Mechanistic-Empirical method The limiting rutting is recommended as 20 mm in
20 per cent of the length for design traffic up to 30 msa and 10 per cent of the length for the design traffic beyond
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Guidelines for Design by IRC: 37: 2012
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Design Traffic: The recommended method considers design
traffic in terms of the cumulative number of standard axles (80 kN) to be carried by the pavement during the design life.
Only the number of commercial vehicles having gross vehicle weight of 30 kN or more and their axle-loading is considered for the purpose of design of pavement.
Assessment of the present day average traffic should be based on seven-day-24-hour count made in accordance with IRC: 9-1972 "Traffic Census on Non-Urban Roads".
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Traffic growth rate (r):
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Estimated by Analyzing: The past trends of traffic growth,
Change in demand of Traffic by factors like specific development, Land use changes etc.
If the data for the annual growth rate of commercial vehicles is not available or if it is less than 5 per cent, a growth rate of 5 per cent should be used (IRC:SP:84-2009).
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Design life (n)
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The design life is defined in terms of the cumulative number of standard axles in msa that can be carried before a major strengthening, rehabilitation or capacity augmentation of the pavement is necessary.
Depending upon road type, Design traffic is ranges from 10 to 15 years.
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Vehicle damage factor (VDF)
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It is defined as equivalent number of standard axles per commercial vehicle.
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.
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Continue ….
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Example on VDF:
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Sample Size for Axle Load Survey:
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Lane distribution factor
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Distribution of commercial traffic in each direction and in each lane is required for determining the total equivalent standard axle load applications to be considered in the design.
In the absence of adequate and conclusive data, the following distribution may be assumed until more reliable data on placement of commercial vehicles on the carriageway lanes are available:
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Lane distribution calculation:
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1) Single-lane roads:
2) Two-lane single carriageway roads:
3) Four-lane single carriageway roads:
4) Dual carriageway roads:
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Computation of Design traffic:
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The design traffic in terms of the cumulative number of standard axles to be carried during the design life of the road should be computed using the following equation:
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Sub-grade
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Requirements of CBR: Sub grade is made up of in-situ material, select soil or stabilized soil.
Compacted to a minimum of 97% of laboratory dry density achieved with heavy compaction.
Minimum CBR of 8% for traffic > 450 CVPD CBR can also be determined from Dynamic
Cone Penetrometer (60º cone) by .. Log10 CBR = 2.465-1.12log10 N Where, N = mm/blow
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Sub-grade (Continue…)
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Where different types of soils are used in sub grade minimum 6 to 8 average value for each type is required.
90th percentile for high volume and 80th percentile for other category of road is adopted as design CBR .
Maximum permissible variation
Where variation is more average CBR should be average of 6 samples and not three.
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Effective CBR
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Where there is significant difference between the CBRs of the select sub grade and embankment soils, the design should be based on effective CBR. The effective CBR of the subgrade can be determined from Fig.
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Lab procedure for CBR calculation:
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The test must always be performed on remoulded samples of soils in the laboratory.
The pavement thickness should be based on 4-day soaked CBR value of the soil, remoulded at placement density and moisture content ascertained from the compaction curve.
In areas with rainfall less than 1000 mm, four day soaking is too severe a condition for well protected sub-grade with thick bituminous layer and the strength of the sub-grade soil may be underestimated.
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Continue ….
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If data is available for moisture variation in the existing in-service pavements of a region in different seasons, molding moisture content for the CBR test can be based on field data.
Wherever possible the test specimens should be prepared by static compaction. Alternatively dynamic compaction may also be used.
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Resilient Modulus:
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Resilient modulus is the measure of its elastic behavior determined from recoverable deformation in the laboratory tests.
The modulus is an important parameter for design and the performance of a pavement.
The relation between resilient modulus and the effective CBR is given as:
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Continue ….
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The CBR of the sub-grade should be determined as per IS: 2720 (Part 16) (36) at the most critical moisture conditions likely to occur at site.
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Principle of pavement design:
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Pavement Model:
Modeled as linear elastic multilayer structure.
Stress Analysis is based on IITPave software
Critical parameters for analysis are
1. Tensile strain at the bottom of bituminous layer
2. Vertical sub-grade strain at the top of sub-grade.
Failure of pavement is considered due to cracking and rutting
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Check for Fatigue:
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Micro cracks at the bottom of bituminous layer are developed with every load repetition
These cracks goes on expending till they propagate to the surface due to the large load repetition
In these guidelines, cracking in 20 per cent area has been considered for traffic up to 30 msa and 10 per cent for traffic beyond that.
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Check for Fatigue (Continue….)
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Two fatigue equations developed based on performance data collected during various study are
Nf= 2.21 * 10-04x [1/εt]3.89* [1/MR]0.854 (80 % reliability)…(a)
Nf= 0.711 * 10-04x [1/εt]3.89* [1/MR]0.854 (90 % reliability)...(b)
Where, Nf= fatigue life in number of standard axles, εt= Maximum Tensile strain at the bottom of the
bituminous layer, and MR= resilient modulus of the bituminous layer.
Equation for 90% reliability implies that only 10% of the pavement area will have more than 20% cracks.
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Check for Fatigue (Continue….)
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To consider the effect of volume of the bitumen and air voids equation (b) is modified as follows
Nf =0.5161 * C * 10-04 x [1/ εt]3.89 * [1/MR]0.854………(c)
Va= per cent volume of air void and Vb= per cent volume of bitumen in a given volume of bituminous mix.
Nf= fatigue life, єt= maximum tensile strain at the bottom of DBM.
MR= Resilient modulus of bituminous mix. For traffic < 30 msa consider equation (a); For traffic >
30msa equation (c) is recommened.
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Check for Rutting:
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Rutting is the permanent deformation in pavement usually occurring longitudinally along the wheel path.
Causes – 1. Deformation in sub grade /non-bituminous layer 2. Secondary compaction and shear deformation
of bituminous layer Limiting value
20 mm in 20% length for upto 30 msa 20 mm in 10% length for > 30 msa
Rutting affects the serviceability of pavement.
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Rutting (Continue …)
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Based on various studies the two equation develops are;
N = 4.1656 x 10-08[1/εv]4.5337 (80 per cent reliability)
N = 1.41x 10-8x [1/εv]4.5337 (90 per cent reliability)
Where, N = Number of cumulative standard axles,
and εv= Vertical strain in the sub-grade
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Pavement composition as per IRC:
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A flexible pavement covered in these guidelines consists of different layers as shown in figure;
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SUB-BASE LAYER
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UNBOUND SUB-BASE LAYER Sub-base materials may consist of natural
sand, moorum, gravel, laterite, kankar, brick metal, crushed stone, crushed slag
Sub-base materials passing 425 micron sieve when tested in accordance with IS:2720 (Part 5) should have liquid limit and plasticity index of not more than 25 and 6 respectively.
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SUB-BASE LAYER(Unbound SB Continue…)
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When coarse graded sub-base is used as a drainage layer, Los Angeles abrasion < 40
Required permeability; fines passing 0.075 mm should be less than 2 per cent.
Sub-base is constructed in two layers, the lower layer forms the separation/filter layer to prevent intrusion of subgrade soil into the pavement and the upper GSB forms the drainage layer to drain away any water
Resilient modulus (MR) for granular sub-base MRgsb = 0.2 h0.45 * MR subgrade Where, h = thickness of sub-base layer in mm
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SUB-BASE LAYER
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Bound Sub base Material for bound sub-base may consist of soil,
aggregate or soil aggregate mixture modified with chemical stabilizers such as cement, lime-flyash.
The drainage layer of the sub-base may consist of coarse graded aggregates bound with about 2 per cent cement while retaining the permeability.
Drainage and separation layers are essential when water is likely to enter into pavements from the shoulder, median or through the cracks in surface layer.
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SUB-BASE LAYER(Unbound SB Continue…)
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Strength Parameter: Elastic Modulus E of bound sub-bases is Ecgsb = 1000 * UCS Where UCS = 28 day strength of the
cementitious granular material
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BASE LAYER
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UNBOUND BASE LAYER Base layer may consist of wet mix macadam,
water bound macadam, crusher run macadam, reclaimed concrete etc.
Resilient modulus of the granular base is given as.. MR granular = 0.2 * h0.45 MR subgrade Where h = thickness of granular sub-base and
base, mm Poisson's ratio of granular bases and sub-
bases is recommended as 0.35.
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BASE LAYER(Continue..)
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CEMENTITIOUS BASES : Cemented base layers may consist of
aggregates or soils or both stabilized with chemical stabilizers, to give a minimum strength of 4.5 to 7 MPa in 7/28 days.
Default values of modulus of rupture are recommended for cementitious bases (MEPDG). Cementitious stabilized aggregates - 1.40 MPa Lime—flyash-soil - 1.05 MPa Soil cement - 0.70 MPa
Poisson's ration of the cemented layers may be taken as 0.25.
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Criteria for selecting Bitumen grade.
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The recommended resilient modulus values of the bituminous materials with different binders are:
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Continue …..
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The Poisson’s ratio of bituminous layer depends upon the pavement temperature and a value of 0.35 is recommended for temperature up to 35°C and value of 0.50 for higher temperatures.
Higher viscosity of bituminous binders, which can be achieved either by using higher viscosity grade bitumen or modified bitumen will improve both fatigue and rutting behavior of mixes as compared to mixes with normal bitumen.
Fatigue equation at any pavement temperature from 20°C to 40°C can be evaluated by substituting the appropriate value of the resilient modulus of the bituminous mix, air void and volume of bitumen. Catalogue of designs has been worked out for a temperature of 35°C.
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Drainage Layer
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Improvement of drainage can significantly reduce the magnitude of seasonal heave. The desirable requirements are: (a). Provision must be made for the lateral drainage
of the pavement structural section. The granular sub-base/base should accordingly be extended across the shoulders
(b). No standing water should be allowed on either side of the road embankment.
(c). A minimum height of1 m between the subgrade level and the highest water level
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Drainage Layer(Continue…)
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Some typical drainage system is illustrated in following Figs….
Fig.1 Pavement along a Slope
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Drainage Layer(Continue…)
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Fig. 2 Pavement with Filter and Drainage Layers
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Drainage Layer(Continue…)
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Criteria to be satisfied: The filter/separation layer should satisfy the following criteria:
To prevent entry of soil particles into the drainage layer:
D85 means the size of sieve that allows 85 per cent by weight of the material to pass through it.
Similar is the meaning of D50 and D15.
DESIGN OF FLEXIBLE PAVEMENT :
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Presented by: Aditya Upadhya (16M150) Aniruddha Chopadekar (16M151) Samarth Bhatia (16M152)
What is design ?
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Design of pavement includes deciding the number of layers, its composition and thickness for selected material, to support traffic load safely without failure.
Various cases in design.
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The flexible pavement with different combinations of traffic loads and material properties.
1) Granular base and Granular sub-base. 2) Cementitious base and sub-base with agg.
Interlayer. 3) Cementitious base and sub-base with SAMI. 4) RAP agg. Over cemented sub-base 5) Cemented base and Granular sub-base
Problem statement.
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Design the pavement for construction of a new flexible pavement with the following data:
Four lanes divided National Highway.
Design life is 15 years.
Data collection
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Material properties :
California Bearing Ratio (CBR) Resilient Modulus (MR) Modulus of Elasticity (E) Poisson’s ratio (µ)
Material properties
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CBR : The CBR values are calculated after every kilometre on selected stretch of 10 km having the same type of soil. Suppose the values obtained are: 3.8, 2.8, 4.5, 3.9, 4.2, 2.9, 4.7, 4.3, 4.0 and 4.6%. Based on the collected data the design CBR (90th percentile CBR) is calculated as below:
Solution :
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Arrange in ascending order : 2.8, 2.9, 3.8, 3.9, 4.0, 4.2, 4.3, 4.5, 4.6 and 4.7.
Calculate the percentage greater than equal of the value as follows:
For CBR of 3.8, percentage of values greater than equal to 3.8 = (8/10) x100 = 80%
Similarly for 2.8 % is 100%, 4.5% CBR is 80% and so on.
Now a plot is made between Percentages of values greater than equal to the CBR values versus the CBR as follows.
Continue …
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RESULT : The 90th Percentile CBR value is 2.90%
Effective CBR:
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(Figure 5.1, Page 11, IRC: 37: 2012)
Poisson’s ratio
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Poisson’s ratio µ is define as the ratio of lateral strain (ɛl) to the axial strain (ɛa), caused by load parallel to the axis along which ɛa is measured.
It is found that for most of the pavement structures, the influence of µ value is normally small.
For most of cement treated materials (soil cement, cement treated base, lean concrete and PCC), the value of µ normally lies between 0.10 and 0.25.
Unbound granular material lie between 0.2 and 0.5 and those for bituminous mixes range from 0.35 to 0.50
Elastic modulus
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Elastic moduli of various pavement materials are obtained either through tests or through the recommendations available in the guidelines.
Repeated flexure or indirect tensile tests are carried out to determine the dynamic modulus Ed of bituminous mixes.
Resilient modulus
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Resilient modulus is the measure of its elastic behaviour determined from recoverable deformation in the laboratory tests.
The behaviour of the subgrade is essentially elastic under the transient traffic loading with negligible permanent deformation in a single pass.
This can be determined in the laboratory by conducting tests.
Calculation of MR for Sub-grade.
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The resilient modulus is calculated as follow;
MR (Mpa) = 10 x CBR …………. For CBR 5
= 17.6 x CBR0.64 ………For CBR > 5
(From equation 5.2, Page no. 12, IRC: 37:
2012)
Calculation of MR for Granular base and sub-base.
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The resilient modulus is calculated as follow;
MRgsb = 0.20 x h0.45 x MR subgrade
h = Thickness of sub-base layer in mm, …… sub-base,
= Cumulative thickness of Base layer and Sub-base layer in mm ... for base
Traffic count
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Assessment of average daily traffic should be normally based on 7 day-24hr count made in accordance with IRC: 9 “Traffic census on non-urban roads”.
Classify traffic into different categories such as two wheelers, three wheelers, passenger cars, trucks etc.
But only commercial vehicle with laden weight > 3 tonne is taken into consideration of design.
Commercial vehicles are further categorised as single axle single wheel, single axel dual wheel, Tandem axle dual wheel and Tridem axle dual wheel.
Where no traffic count data is available, data from roads of similar classification and importance may be used to predict the design traffic
Calculation of Design factor
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1) Design Traffic, 2) Axle load survey, 3) Vehicle Damage Factor 4) Lane Distribution Factor
Design Traffic:
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Initial traffic after construction in terms of number of Commercial Vehicles per day (CVPD).
Traffic growth rate during the design life in percentage.
Design life in number of years. Spectrum of axle loads. Vehicle Damage Factor (VDF). Distribution of commercial traffic over the
carriageway.
Calculation of Design traffic:
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For our case the number of heavy commercial vehicle per day is taken as 7 day average for 24 hour count comes to be 2792 vehicle per day as per the last count.
i. e. P = 2792 cvpd, r = 7 %, and x = 10 years
A = 2792 (1+0.07)10 = 5000 cvpd.
RESULT: Traffic in the year of completion of construction is 5000 cvpd in both the directions.
Axle load survey :
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Required for VDF calculation and Fatigue damage analysis of cementitious base.
The axle load spectrum is formulated by considering 10 kN, 20 kN and 30 kN intervals for single, tandem and tridem axle respectively.
RESULT: As per study the percentage of Single, Tandom and Tridom axle are 45%, 45% and 10% respectively
Axle load spectrum
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Single Axle Load Tandem Axle Load Tridem Axle Load
Axle load Class (KN)
Percentage of Axles
Axle load Class (KN)
Percentage of Axles
Axle load Class (KN)
Percentage of Axles
185-195 0.64 390-410 1.85 585-615 1.40
175-185 0.80 370-390 2.03 555-585 1.60
165-175 0.80 350-370 2.03 525-555 1.60
155-165 2.58 330-350 2.08 495-525 1.80
145-155 2.58 310-330 2.08 465-495 1.80
135-145 5.80 290-310 4.17 435-465 4.40
125-135 5.80 270-290 4.17 405-435 4.40
115-125 11.82 250-270 12.67 375-405 13.10
105-115 11.82 230-250 12.67 345-375 13.10
95-105 12.90 210-230 10.45 315-345 10.90
85-95 12.16 190-210 10.45 285-315 10.40
< 85 32.30 170-190 7.05 255-285 7.15
<170 28.28 <255 28.33
Total 100 100 100
Vehicle damage factor
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The formula to calculate VDF is given as follows:
W1, W2, ….. are the mean values of the various axle load groups.
V1, V2, …. are the respective traffic volumes. Ws is the standard axle load. Standard axle load for Single axle, Tandem axle and
Tridem axle is 80 KN, 148 KN and 224 KN as per IRC: 37:2012 (Page 7)
RESULT: The VDF for Single axle load, Tandem axle load and Tridem axle load is 4.11, 8.37 and 7.51.
Vehicle Damage factor (Continue.)
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Were sufficient information on axle loads are not available or the small size of project does not warrant an axle load survey the default values of VDF may be adopted as given in the table given below.
Lane distribution factor.
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Distribution of commercial traffic in each direction and in each lane is required for determining the total equivalent standard axle load applications to be considered in the design.
Single lane road : Total vehicle in both direction.
Two lane single carriage way : 50% of total vehicle in both direction.
Four lane single carriage way : 40% of total vehicle in both direction.
Dual carriage way: Two lane 75%, Three lane 60%, Four lane 45% of number of CV in each direction.
Lane distribution factor (Continue….)
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RESULT: In the present design problem we are given to design a four lane divided highway, therefore the Lane distribution factor is 75 percent of number of commercial vehicle in each direction.
Million standard axle
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The design traffic is calculated in terms of cumulative number of standard axle of 80 kN carried during the design life of the road.
r = 7.5 %, n = 20 yr. ( Expressway and Urban roads), 15 yr
(NH and SH), In this problem we have to design National highway take n as 15 years,
A is 5000cvpd in both direction and 2500 in one direction
Calculation of Million std. axle.
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Single axle load (N1): 45 percent vehicles are of single axle.A : 0.45 x 2500 = 1125, F : 4.11
N1 = 33.06 x 106 = 33.06 msa
Tandem axle load (N2): 45 percent vehicles are of tandem axle.A : 0.45 x 2500 = 1125, F : 8. 37N2 = 67.33 x 106 = 67.33 msa
Tridem axle load (N3): 10 percent vehicles are of tridem axle.A : 0.10 x 2500 = 250, F : 7.51N2 = 13.42 x 106 =13.42 msa
Calculation of Million std. axle. (Continue…)
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Total msa (N1+N2+N3) = 33.06 + 67.33 + 13.42
= 113.81 ̴ 150 msa (Aprox.)
RESULT: The cumulative million standard axles to be consider for design is 150 msa.
Determination pavement thickness
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Case 1 : Bituminous pavement with untreated granular layer
Determination of thickness for Case 1
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The thickness of various layers is determined with the help pavement design catalogue given in IRC: 37: 2012 from page 26 to 28, for various values of effective CBR.
Determination of thickness for Case 1 (Continue ….)
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RESULT: For design traffic of 150msa and CBR of 7% Thickness of subbase (GSB) is 230 mm, Thickness of base (G. Base) is 250 mm, Thickness of Dense Bitumen macadam (DBM)
is 140 mm, Thickness of Bituminous concrete (BC) is 50
mm
Case 2 : Bituminous pavement with cemented base and cemented sub-base with aggregate inter layer of 100mm
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Continue ….
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Determination of thickness for case 2.
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RESULT: For design traffic of 150msa and CBR of 7% Thickness of Cementitious sub-base (CT
Subbase) is 250 mm, Thickness of Cementitious base (CT Base) is
120 mm, Aggregate interlayer is 100mm Thickness of Dense Bitumen macadam (DBM)
is 50 mm Thickness of Bituminous concrete (BC) is 50
mm are Obtained by interpolating the thickness of
CBR 5% and 10%.
Calculation of Resilient Modulus (MR) for case 2
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MR subgrade = 17.6 x CBR0.64 = 17.6 x 70.64 = 61.15 Mpa.
MR Bituminous layer = 3000 Mpa (From table 7.1 Resilienent Modulus of Bituminous Mixes, page 23, IRC: 37: 2012)
Pavement composition for 90 per cent Reliability is BC + DBM = 100 mm,
Aggregate interlayer = 100 mm (MR = 450 MPa),
Cemented base = 120 mm (E = 5000 MPa), Cemented subbase = 250 mm (E = 600 Mpa)
Case 3 : Bituminous pavement with cemented base and cemented sub-base with SAMI layer over cemented base.
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Continue ….
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PAGE 33 AND 34 OF IRC: 37: 2012
Determination of thickness for Case 3
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RESULT: Design traffic of 150 msa and CBR of 7% thickness of Cementitious sub-base (CT
Subbase) is 250 mm, Thickness of Cementitious base (CT Base) is
165 mm, Thickness of Dense Bitumen macadam (DBM)
is 50 mm Thickness of Bituminous concrete (BC) is 50
mm are obtained by interpolating the thickness of CBR
5% and 10%. SAMI is provided on the top of cemented base.
Case 4 Bituminous pavement with base of fresh aggregate or RAP treated with foamed bitumen/ Bitumen emulsion and cemented sub-base
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Continue …
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PAGE 36 AND 37 OF IRC: 37: 2012
Determination of thickness for case 4
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RESULT: Design traffic of 150 msa and CBR of 7% Thickness of Cementitious sub-base (CT Subbase) is
250 mm, Thickness of Treater reclaimed aspalt pavement
(Treated RAP) is 180 mm, Thickness of Dense Bitumen macadam (DBM) is 50 mm Thickness of Bituminous concrete (BC) is 50 mm are Obtained by interpolating the thickness of CBR 5% and
10%. Instead of RAP base of fresh aggregates treated with
bitumen emulsion/ foamed bitumen can be used to obtain stronger base.
Case 5 : Bituminous pavement with cemented base and granular sub-base with 100mm WMM layer over cemented base:
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Continue …
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Determination of thickness for case 5
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RESULT: Design traffic of 150 msa and CBR of 7% Thickness of Granulated Subbase (GSB) is 250 mm Cementitious sub-base (CT Subbase) is 195 mm, Thickness of aggregate layer is 100 mm, Thickness of
Dense Bitumen macadam (DBM) is 50 mm Thickness of Bituminous concrete (BC) is 50 mm Obtain by interpolating the thickness of CBR 5% and
10%. The upper 100 mm of granular sub-base should be
open graded so that its permeability is about 300 mm/day or higher for quick removal of water entering from surface.
Calculation of Resilient Modulus (MR) and Modulus of Elasticity (E):
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For traffic of 150 msa, Subgrade CBR 7%, MR subgrade = 17.6 x CBR0.64 = 17.6 x 70.64 = 61.15
Mpa. MR Bituminous layer = 3000 Mpa (From table 7.1
Resilienent Modulus of Bituminous Mixes, page 23, IRC: 37: 2012)
MR Aggregate = 450 Mpa and E of cemented base is 5000 MPa, E Granular subbase = MR subgrade x 0.20 x h0.45 Where, h = Thickness of GSB = 250 mm = 61.15 x 0.20 x 2500.45 = 146.72 Mpa.
Design check
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To check the suitability of pavement design discussed above we carry out checks, which ensure safety against the failure of designed pavement.
The flexible pavement is checked for two types of failures i.e. Rutting in pavement and Fatigue in bottom layer of bituminous surfacing.
The following condition should be satisfied for the design to be satisfactory
Design strain < Allowable strain Allowable strain = Obtained by fatigue model
and rutting model Design strain = IITpave software
Design of Drainage layer
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Design a granular drainage layer for a four lane heavy duty divided highway for an annual precipitation of 1200 mm. Longitudinal slope = 3 per cent, Camber = 2.5 percent.
Crack Infiltration Method
Continue ... Depth of drainage layer = 450 mm (WMM
250mm and Sub-base 200mm) By design. Width of drainage layer : Calculate
AB = 8.5+1+2x0.45 = 10.4 m (1m unpave shoulder)
AC = 10.4 x(3/2) = 12.48 m. AD = 16.24 m
(hypotenious of AB and AC) Elevation drop :
Along AC: 12.48x3% = 0.374m Along CD: 10.40x2.5% = 0.26m Total drop = 0.634
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Continue …. Hydraulic gradient = [Elevation drop/ length
AD] = [0.634/16.24] =0.039
Infiltration rate calculation: qi = Ic [Nc/Wp + Wc / (Wp.Cs)]
Ic = 0.223 cub. m/day/meter Nc = 3 Wp = 10.4 m Wc = Wp, Cs = 12 m q = 0.083 Cub.meter/day/meter 26/10/2016119
Continue. Amount of water infiltrated (Q); Q = 0.083 x 1 x 16.24 = 1.35 Cub.meter/ day. Compare with Q = KIA
A = Area of cress section = 1 x 0.1 = 0.1 sq.m K = Coeff of permeability (Unknown) I = Hydraulic gradient (0.039)
1.35 = K x 0.039 x 0.1 K = 346.62 m/day This value of K is useful for deciding
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(Decide grade by using table)% Passing
Sieve Opening,
Mm
Grading 1 Grading 2 Grading 3 Grading 4 Grading 5 Grading 6
20 100 100 100 100 100 10012.5 85 84 83 81.5 79.5 759.5 77.5 76 74 72.5 69.5 634.76 58.3 56 52.5 49 43.5 322.36 42.5 39 34 29.5 22 5.82.00 39 35 30 25 17 00.84 26.5 22 15.5 9.8 0 00.42 18.2 13.3 6.3 0 0 00.25 13.0 7.5 0 0 0 00.10 6 0 0 0 0 00.075 0 0 0 0 0 0
Coeff. Ofpermeability
m/day3 35 100 350 850 950
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Provide Grading 4 for K 346.62 m/day = 350m/day
Recommendation
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Specifications should be modified according to local condition. In wet climate wearing course should be impermeable.
long duration and low intensity rainfall causes more damage as compare with rainfall of small duration and more density.
If DBM and SDBC/BC are designed properly (4% air voids and protected shoulder) impermeably can be ensure.
Adequate provision for sub-surface drainage prevent pavement damage.
Recommendations. Thickness charts with BC/ SDBC are valid for
all rainfall area. For pavement carrying heavy traffic wearing
course laid over WBM shows better performance.
For low traffic (upto 5 msa) bitumen surfacing with two coats is found to be suitable.
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Conclusion
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Time to time revisions of code provision are needed keeping in view changes in traffic pattern and development of new technologies. Further with the gain of experience in the design as well as construction procedure of flexible pavement have demanded certain changes.
Hence by considering the above factors IRC: 37: 2012 includes some conceptual changes in the design of flexible pavement such as inclusion of Resilience moduli and consideration of strain in design.
Conclusion .
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This code also encourages the use IIT pave software which is newly recommended.
Since the use of semi-mechanistic approach, the design is not only based on the experience but it also gives parameters (strain parameter) to check the obtained design.
Solution to the above pavement design problem shows that the thickness design varies with the variation in various factors.
References
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[1] IRC: 37: 2012, “Guidelines for Design of Flexible pavement”, second revision.
[2] IRC: 37: 2001, “Tentative guidelines for Design of Flexible pavement”
Thank you .
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