dr. p. nanjundaswamy department of civil engineering s j ...temperature oc 20 25 30 35 40 bc &...
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Dr. P. NANJUNDASWAMYDepartment of Civil Engineering
S J College of EngineeringMysore – 570 006
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In this Presentation
Introduction
Design Criteria
Failure Criteria
Design Procedure
Pavement Thickness Design Charts
Pavement Composition
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Introduction
Flexible pavement design given in the previous edition (IRC : 37-1984) were applicable to design traffic up to only 30 msa
The earlier code was empirical in nature which has limitations regarding applicability and extrapolation
The present guidelines (IRC : 37-2001) follows mechanistic empirical approach and developed new set of designs up to 150 msa
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Introduction
It is applicable to Expressways, NH, SH, MDR and other categories of roads predominantly carrying motorised vehicles
It is applicable to new pavements
Pavements are considered to include bituminous surfacing and granular base and sub-base courses confirming to IRC/MORTH standards
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Design Criteria
Three main types of critical distresses
Rutting failure due to permanent deformation in sub grade
Rutting due to permanent deformation in bituminous layer
Fatigue cracking in bituminous ( top surface) layer.
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Design Criteria . . . .
Rutting Failure
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Design Criteria . . . .
Fatigue Cracks
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Design Criteria . . . .
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Design Criteria . . . .
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Failure Criteria
Fatigue criteria
Nf= Cumulative std. axle load repetitions before the
pavement develop 20% Cracking
εt= Initial horizontal tensile strain at the bottom of
bituminous layer
E= Elastic modulus of bituminous layer in Mpa
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Failure Criteria . . . .
Rutting criteria
Nr= Cumulative std. axle load repetitions before
the pavement develop 20 mm rut depth
εz= Initial vertical strain at the top of subgrade
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Design Approach
Selection of appropriate inputs for
Climatic condition
Pavement layers – no & composition
Material characterisation
Traffic characterisation
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Design Approach
Based on the inputs perform trial design
Assign material properties (E & μ)
Consider standard loading
Use linear elastic layered theory
Compute critical response
Compare with failure criteria
Revise the thickness if needed
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Estimation of Design Traffic
Design Traffic
Initial traffic (CVPD)
Traffic growth rate
Design period
VDF LDF
Traffic in the year of completion
P = no of commercial vehicles as per last countx = no of years between year of last count and
year of completion of construction
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Material Characterisation
Modulus of Elasticity (E)
Sub-grade
10 * CBR for CBR ≤ 5%
176 * CBR0.64 for CBR > 5%
Granular Sub-base and Base
Esubgrade * 0.2 * h0.45
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Material Characterisation
Modulus of Elasticity (E) Bituminous materials
Mix TypeTemperature oC
20 25 30 35 40
BC & DBM 80/100 bitumen 2300 1966 1455 975 797
BC & DBM 60/70 bitumen 3600 3126 2579 1695 1270
BC & DBM 30/40 bitumen 6000 4928 3809 2944 2276
BM 80/100 - - - - - - 500 - -
BM 60/70 - - - - - - 700 - -
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Material Characterisation
Poisson’s Ratio (μ)
Sub-grade and granular layer
μ = 0.4
Bituminous Layer
Pavement temp 35o-40o C, μ = 0.50
Pavement temp 20o-30o C, μ = 0.35
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Standard Load Considered
Standard Axle Load = 80 kN
one dual wheel set is only considered i.e., Pd = 20 kN
Tyre pressure = 0.56 MPa
Center to Center spacing of tyres, Sd = 310 mm
h1 E1, µ1
∞
E2, µ2
E3, µ3
h2
Pd Pd
Sd
Sd/2
εz
εh
A B
C
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Design Tables & Charts
Designs are given for
Sub-grade CBR values : 2% to 10%
Design traffic : 1 msa to 150 msa
Pavement temperature 35o C
Input parameters
Design traffic in terms of cumulative number of standard axles
CBR value of Sub-grade
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Design Charts
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Design Charts
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Design Tables & Charts
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Pavement Composition
Pavement Composition
Sub-base Base Surface
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Pavement Composition
Sub-base Course
Natural sand, gravel, laterite, brick metal, crushed stone or combinations thereof
Minimum CBR :
20% upto 2 msa traffic30% exceeding 2 msa
Minimum Thickness
150 mm for traffic < 10 msa200 mm for traffic ≥ 10 msa
If subgrade CBR < 2%, design for subgrade CBR of 2% and provide a 150 mm thick capping layer of minimum CBR 10%
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Pavement Composition
Base Course
Unbound granular material – WBM, WMM, …
Minimum CBR :
20% upto 2 msa traffic30% exceeding 2 msa
Minimum Thickness
225 mm for traffic ≤ 2 msa250 mm for traffic > 2 msa
If WBM is used and traffic > 10 msa, minimum thickness is 300 mm (4 layers of 75 mm each)
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Pavement Composition
Bituminous Surfacing
Wearing course or Binder course+wearing course
Wearing course : Surface dressing, open-graded premix carpet, mix seal surfacing, SDBC and BC
Binder course : BM, DBM, mix seal surfacing, SDBC and BC
Wearing surface used is open-graded premix carpet of thickness upto 25 mm, it should not be counted towards the total thickness
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Final Remarks
The present guidelines follows mechanistic empirical approach and developed new set of designs up to 150 msa
Thickness charts are still available for CBR values of up to 10% only
Design charts are available for only a pavement temperature of 35o C
The contribution of individual component layers is still not realized fully with the system of catalogue thicknesses. The same can be done with the analytical tool for design.
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Thank you