First brought out in 1970, based on

California Bearing Ratio (CBR) of subgrade and

traffic in terms of number of commercial vehicles

(more than 3 tonnes laden weight).

Revised in 1984, based on

California Bearing Ratio (CBR) of subgrade and

design traffic in terms of cumulative number of

equivalent standard axle load of 80 kN in millions of

standard axles (MSA) and

design charts were provided for traffic up to 30 msa using

an empirical approach. .

History of IRC 37 – Flexible Pavement

The guidelines were revised again in 2001

Designed For Traffic As High As 150 Msa.

Based On Semi-mechanistic Approach

Based on the results of the MORTH’s research scheme

R-56 implemented at IIT Kharagpur. FPAVE was developed

Multilayer elastic theory was adopted for stress analysis

of the layered elastic system. A large number of data collected from different parts of India under various research schemes of MORTH were used for the development of fatigue and rutting criteria from field performance data

History of IRC 37 – Flexible Pavement

The IRC: 37-2001 based on a Mechanistic Empirical approach, the design life of pavement …. is, till the fatigue cracking in bituminous surface extended to 20 per cent of the pavement surface area or rutting in the pavement reached the terminal rutting of 20 mm, whichever happened earlier.

The IRC: 37-2012 based on a Scientific cum Mechanical approach, the design life of pavement …. Is, the same approach except that the cracking and rutting have been restricted to 10 per cent of the area for design traffic exceeding 30 MSA

Design concepts of IRC 37 – Flexible Pavement

These revised guidelines aim at

Pavement design by including alternate materials like

cementitious and reclaimed asphalt materials

Analysis using the software IITPAVE, a modified version

of FPAVE developed under the Research Scheme R-56

Design concepts of IRC 37 – Flexible Pavement

SCOPE OF THE GUIDELINES – IRC 37-2012

Flexible pavements include pavements with Bituminous surfacing over:

(i) Granular base and sub-base

(ii) Cementitious bases and sub-bases with a crack relief layer of aggregate

interlayer below the bituminous surfacing

(iii) Cementitious bases and sub-bases with SAMI in-between bituminous

surfacing and the cementitious base layer for retarding the reflection

cracks into the bituminous layer

(iv) Reclaimed Asphalt Pavement (RAP) with or without addition of fresh

aggregates treated with foamed bitumen/bitumen emulsion

(v) Use of deep strength long life bituminous pavement

(i) Incorporation of design period of more than fifteen years.

(ii) Computation of effective CBR of subgrade for pavement

design.

(iii) Use of rut resistant surface layer.

(iv) Use of fatigue resistant bottom bituminous layer.

(v) Selection of surface layer to prevent top down cracking.

(vi) Use of bitumen emulsion/foamed bitumen treated

Reclaimed Asphalt Pavements in base course.

New elements of IRC 37 – 2912

(vii) Consideration of stabilized sub-base and base with

locally available soil and aggregates.

(viii) Design of drainage layer.

(ix) Computation of equivalent single axle load considering

(a) single axle with single wheels (b) single axle with dual

wheels (c) tandem axle and (d) tridem axles.

(x) Design of perpetual pavements with deep strength

bituminous layer.

New elements of IRC 37 – 2912

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design of flexible pavement

Design based on multiple layer elastic theoryInfluencing FactorsSub-grade conditionsWheel loadTraffic intensityClimateTerrain

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Traffic Data required

Initial traffic after construction in terms of Commercial Vehicles Per Day Commercial vehicle – Having more than 3 tonne axle load

Traffic growth rate during the design lifeDesign life in no. of yearsVehicle damage factorDistribution of commercial vehicle over the

carriageway

TRAFFICTraffic Projection based on

(i) The past trends of traffic growth(ii) Demand of traffic with respect to macro-economic parameters (like GDP or SDP) and (iii) expected demand due to specific developments and land use changes likely to take place during design life.

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). ( as per Cl 4.2.2 of IRC 37-2012)

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Design life

• Expressways Design life is 20 Years• NH and SH, Design life is 15 Years• For MDR, design life of 10 to 15 Years• For ODR, Design life is 10 Years Stage ConstructionReason : Cost constrainsa) Base and Sub base are designed for Full design lifeb) Bituminous layers for Less years,

but not less than 5 years in any case

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Vehicle Damage factor

It is multiplier to convert the number of commercial Vehicle of different axle loads and axle configuration to Standard configuration

Arrived from Axle load SurveyFactors considered:Traffic MixMode of transportationCommodities CarriedSeason of the yearRoad conditionDegree of Enforcement

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Vehicle Damage factor

Sl No Initial Traffic after

Completion of Traffic in CVPD

Indicative VDF Value

Rolling / Plain

Hilly

1 0 - 150 1.50 0.50

2 150 - 1500 3.50 1.50

3 More than 1500 4.50 2.50

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Lane Distribution Factor

Realistic assessment of Distribution of Commercial Vehicle by Lane

Single Lane 1.00

Intermediate Lane 1.00

Two Lane Single Carriage way 0.50Four Lane Single Carriage way 0.40

Dual Carriage way (Each Direction)

Two Lane

Three Lane

Four Lane

0.75

0.60

0.40

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Design Traffic in MSA

N = 365 X ((1+r)n – 1)x A x D X F

rN = Cumulative Standard Axle over Design lifeA = Initial traffic after construction in terms of

Commercial Vehicles Per Day, D=Lane Distribution factorF = Vehicle Damage Factorr = Annual Growth Rate

A = P (1 + r)x

P = Traffic in CVD as per last count, x = Number of years between last count and

Completion of Project

SUBGRADEThe select soil forming the subrade should have a minimum CBR of 8 per cent for roads having traffic of 450 commercial vehicles per day or higher.

Number of tests, design value and tolerance limitWhere different types of soils are used in subgrade,a minimum of six to eight average CBR values (average of three tests) for each soil type

90th percentile of CBR - for high volume roads such as Expressways, National Highways and State Highways. 80th percentile of CBR - For other categories of roads, (MDR & ODR)

The following example illustrates the procedure for finding the design.

16 CBR values for a highway alignment are as follows: 3.5, 5.2, 8.0, 6.8, 8.8, 4.2, 6.4, 4.6, 9.0, 5.7, 8.4, 8.2, 7.3, 8.6, 8.9, 7.6

Arrange the above 16 values in ascending order 3.5, 4.2, 4.6, 5.2, 5.7, 6.4, 6.8, 7.3, 7.6, 8.0, 8.2, 8.4, 8.6, 8.8, 8.9, 9.0

For CBR of 3.5, percentage of values greater than equal to 3.5 = (16/16) * 100 = 100

For CBR of 4.2, percentage of values greater than equal to 4.2 = (15/16) * 100 = 93.75 and so on.

Now a plot is made between percentages of values greater than equal and the CBR values versus the CBR as follows.

The 90th percentile CBR value = 4.7, and 80th percentile CBR = 5.7 in. Asphalt Institute of USA (6) recommends 87.5 percentile subgrade modulus for design traffic greater than one msa.

Effective CBR

PAVEMENT COMPOSITION

Stress Absorbing Membrane Interlayer (SAMI) of elastomeric modified binder at the rate of about 2 litre/m2 covered with light application of 10 mm aggregates to prevent picking up of the binder by construction traffic(AUSTROADS). Sub-base layer

The sub-base should be composed of two layers, the lower layer forms the separation/filter layer to prevent intrusion of subgrade soil into the pavement (Grading III & IV) and the upper GSB forms the drainage layer to drain away any water that may enter through surface cracks. (Grading V & VI) The drainage layer should be tested for permeability and gradation may be altered to ensure the required permeability. Filter and drainage layers can be designed as per IRC: SP: 42-1994 (33) and IRC: SP: 50-1999(34).(7.2.1.3 of IRC 37-2012)

Determination of Resilient Modulus

The behaviour of the subgrade is essentially elastic under the transient traffic loading with negligible permanent deformation in a single pass. Resilient modulus is the measure of its elastic behaviour determined from recoverable deformation in the laboratory tests.

The relation between resilient modulus and the effective CBR is given as:

MR (MPa) = 10 * CBR for CBR 5 = 17.6 * (CBR)0.64 for CBR > 5

MR = Resilient modulus of subgrade soil.

Strength parameter

The relevant design parameter for granular sub-base is resilient modulus (MR), which is given by the following equation:

MRgsb = 0.2*h0.45 * MR subgrade

Where h = thickness of sub-base layer in mm

MR value of the sub-base is dependent upon the MR value of the subgrade since weaker subgrade does not permit higher modulus of the upper layer because of deformation under loads.

Bituminous layers

depends upon the pavement temperature a value of 0.35 is recommended for temperature up to 35°C value of 0.50 for higher temperatures.

Poisson’s ratio of granular bases and sub-bases is recommended as 0.35.

Poisson’s ratio

Resilient Modulus of Bituminous Mixes, MPa

Mix type Temperature °C 20 25 30 35 40

BC and DBM for VG10 bitumen 2300 2000 1450 1000 800

BC and DBM for VG30 bitumen 3500 3000 2500 1700 1250

BC and DBM for VG40 bitumen 6000 5000 4000 3000 2000

BC and DBM for Modified Bitumen (IRC: SP: 53-2010) 5700 3800 2400 1650 1300

BM with VG 10 bitumen 500 MPa at 35°CBM with VG 30 bitumen 700 MPa at 35°C

WMM/RAP treated with 3 per cent bitumen emulsion/foamed bitumen (2 per cent residual bitumen and 1 per cent cementatious material).

600 MPa at 35°C (laboratory values vary from 700 to 1200 MPa for water saturated samples).

Using Design catalogues

Note:(a)These charts are to be used for traffic above 2 msa. For traffic below 2 msa IRC SP 72-2007 should be referred to. City roads should be designed for minimum 2 msa traffic.

(b) Thickness design for traffic between 2 and 30 msa is exactly as per IRC 37-2001.

(c) In all cases of cementitious sub-bases (i.e. cases 2,3 and 4 above) the top 100 mm thickness of sub-base is to be porous and act as drainage layer

Clarifications: (based on MORTH Rev. 5, 2013 and IRC 37, 20121.Wearing course: SDBC shall not be used as per MORTH Rev.V 20132.Thickness of Bituminous base shall not be less than 50mm 3.BC shall be used in 30mm, 40mm, 50mm based on the design requirement

Clarifications: (based on MORTH Rev. 5, 2013 and IRC 37, 2012)

1.Wearing course: SDBC shall not be used as per MORTH Rev.V 2013

2.Thickness of Bituminous base shall not be less than 50mm

3.BC shall be used in 30mm, 40mm, 50mm based on the design requirement

2 to 5 msa : 30 BC

5 to 10 msa : 30 /40 BC

10 to 100 msa : 40 BC

>100 msa : 50 BC

4.Wherever 30mm BC is provided instead of 25mm SDBC, 5mm shall be

reduced in DBM thickness provided the thickness of DBM is more than 50mm

5. For widening / formation / strengthening using CBR method, BM shall

not be used.

6. Interpolation of layer thickness from the design catalogue is not

permitted

7. For all the design IITPAVE software should be run and output should

be enclosed

8. For new formation/ rebuilding GSB shall be laid in two layers

1. Filter layer at bottom

2. Drainage layer at top

9. CBR of select subgrade shall be 8 or more

Clarifications: (based on MORTH Rev. 5, 2013 and IRC 37, 2012)

PAVEMENT DESIGN PROCEDURE

Using IITPAVE

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Critical locations in pavement

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Design approach and criteria

Vertical compressive strain at the top of the sub-grade

Horizontal compressive strain at the bottom of the bituminous layer

Permanent deformation with in bituminous layers

PRINCIPLES OF PAVEMENT DESIGN

CRITICAL PARAMETERS FOR PAVEMENT DESIGN

Tensile strain, Єt, at the bottom of the bituminous layer and The vertical subgrade strain, Єv, on the top of the subgrade to limit cracking and rutting in the bituminous layers and non-bituminous layers respectively.

6.2.2 Fatigue Model

Nf = 2.21 * 10-04 x [1/εt]3.89 * [1/MR]0.854

(80 per cent reliability) Nf = 0.711 * 10-04 x [1/εt]3.89 * [1/MR]0.854

(90 per cent reliability)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.

6.3.2 Rutting model

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 subgrade

Design procedure

1)Find design Traffic (MSA) as per existing procedure with growth

rate of 5% and LDF for two lane undivided carriageway as 0.50

2)Using CBR arrive at the tentative design layer thickness from

catalogue

3)Calculation resilient modulus (MR) by

a. using equation 5.2 for sub-grade

b. using equation 7.1 for sub-base and base

c. using table 7.1 for bituminous mixes for the relevant pavement

temperature

4) Calculate allowable tensile strain (εt) at the bottom

of bituminous layer using equations in 6.1 or 6.2

5) Calculate allowable vertical strain (εv) using

equation 6.4 or 6.5

6) Using IITPAVE calculate the actual tensile strain and

vertical strain and check whether the values are

within allowable values as calculated in 4) and 5)

Design procedure

Design procedure… How to use IIT Pave1)Input value for calculation of tensile strain and vertical strain using IITPAVE

• Poisson’s ratio shall be 0.35 for granular layers

• The Poisson’s ratio of bituminous layer is 0.35 for

temperature up to 35°C and is 0.50 for higher

temperatures.

• While using IITPAVE, the layer properties shall be entered

in the order from top bituminous layer to bottom subgrade

layer .

• Wheel load shall be 20500 N and type pressure shall be

entered as 0.56 (Mpa)