cee 320 winter 2006 engr. ejaz ahmad khan deputy director pakhtunkhwa highways authority...
Post on 15-Jan-2016
224 Views
Preview:
TRANSCRIPT
CE
E 3
20W
inte
r 20
06
Engr. Ejaz Ahmad Khan
Deputy DirectorPakhtunkhwa Highways Authority
PRESENTATION ON
ROAD PAVEMENT DESIGN BY
CE
E 3
20W
inte
r 20
06
CEE 320Steve Muench
CE
E 3
20W
inte
r 20
06
OUTLINE
• Pavement Structure
Section - 1
Section - 2
• Design of Pavement Structure
Section - 3
• Flexible Pavement DesignSection - 4
• How to DesignSection - 5
• Practical Example
CE
E 3
20W
inte
r 20
06
Section - 1
Pavement Structure
CE
E 3
20W
inte
r 20
06
Combination of various layers between road top surface / Finished Road Level (FRL) and the subgrade is known as pavement
structure. Pavement
Structure:
PAVEMENT :
CE
E 3
20W
inte
r 20
06
PAVEMENT PURPOSE
• Load support• Skid Resistance• Good ride• Less VOC• Time Saving• Drainage
CHAPPAR - DARBAND ROAD (30 KM) PHASE-I
CE
E 3
20W
inte
r 20
06
• Pavements are subjected to moving traffic loads that are repetitive in nature.
• Each traffic load repetition causes a certain amount of damage to the pavement structure that gradually accumulates over time and eventually leads to the pavement failure.
• Thus, pavements are designed to perform for a certain life span before reaching an unacceptable degree of deterioration.
• In other words, pavements are designed to fail. Hence, they have a certain design life.
PHILOSOPHY OF PAVEMENTS
CE
E 3
20W
inte
r 20
06
PAVEMENT TYPES• Flexible Pavement
– Hot mix asphalt (HMA) pavements– Called "flexible" since the total pavement
structure bends (or flexes) to accommodate traffic loads
– The load transmit to the subgrade through particle to particle contact.
• Rigid Pavement– Portland cement concrete (PCC) pavements– Called “rigid” since PCC’s high modulus of
elasticity does not allow them to flex appreciably
– The load transmit to subgrade through beam action.
CE
E 3
20W
inte
r 20
06
FLEXIBLE PAVEMENT
• Structure– Surface course– Base course– Subbase course– Subgrade
CE
E 3
20W
inte
r 20
06
RIGID PAVEMENTS
Thus in contrast with flexible pavements the depressions which occur beneath the rigid pavement are not reflected in their running surfaces.
In rigid pavements the stress is transmitted to the sub-grade through beam/slab effect. Rigid pavements contains sufficient beam strength to be able to bridge over localized sub-grade failures and areas of inadequate support.
CE
E 3
20W
inte
r 20
06
RIGID PAVEMENT
• Structure– Surface course– Base course– Subbase course– Subgrade
CE
E 3
20W
inte
r 20
06
Section - 2
Design of Pavement Structure
CE
E 3
20W
inte
r 20
06
Pavement Thickness Design is the determination of required thickness of various pavement layers to protect a given soil condition for a given wheel load.
Given Wheel Load
150 Psi
3 Psi
Given In Situ Soil Conditions
Asphalt Concrete Thickness?Base Course Thickness?
Subbase Course Thickness?
PAVEMENT THICKNESS DESIGN
CE
E 3
20W
inte
r 20
06
DESIGN PARAMETERS
• Subgrade• Loads• Environment
CE
E 3
20W
inte
r 20
06
SUBGRADE• Characterized by strength and/or
stiffness – California Bearing Ratio (CBR)
• Measures shearing resistance
• Units: percent• Typical values: 0 to 20
– Resilient Modulus (MR)• Measures stress-strain
relationship• Units: psi or MPa• Typical values: 3,000 to
40,000 psi
Picture from University of TokyoGeotechnical Engineering Lab
CE
E 3
20W
inte
r 20
06
SUBGRADE
Some Typical Values
Classification CBR MR (psi) Typical Description
Good ≥ 10 20,000 Gravels, crushed stone and sandy soils.
Fair 5 – 9 10,000 Clayey gravel and clayey sand, fine silt soils.
Poor 3 – 5 5,000 Fine silty sands, clays, silts, organic soils.
CE
E 3
20W
inte
r 20
06TRAFFIC LOADS
CHARACTERIZATION
Pavement Thickness Design Are Developed To Account For The Entire Spectrum Of Traffic Loads
Cars Pickups Buses Trucks Trailers
CE
E 3
20W
inte
r 20
06
Equivalent
Standard ESAL
Axle Load
18000 - Ibs
(8.2 tons)
Damage per Pass = 1
• Axle loads bigger than 8.2 tons cause damage greater than one per pass
• Axle loads smaller than 8.2 tons cause damage less than one per pass
• Load Equivalency Factor (L.E.F) = (? Tons/8.2 tons)4
EQUIVALENCY FACTOR
CE
E 3
20W
inte
r 20
06
Consider two single axles A and B where: A-Axle = 16.4 tons
Damage caused per pass by A -Axle = (16.4/8.2)4 = 16
This means that A-Axle causes same amount of damage per pass as caused by 16 passes of standard 8.2 tons axle i.e.,
8.2 Tons Axle
16.4 Tons Axle
=
EXAMPLE
CE
E 3
20W
inte
r 20
06
1.0
1.1 2.3 3.3
4.7 6.5 8.
711
.5 14.9 18
.9 23.8 29
.5 36.3 44
.1 53.1
63.4 75
.2
0
10
20
30
40
50
60
70
80D
AM
AG
E P
ER
PA
SS
8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
SINGLE AXLE LOAD (Tons)
AXLE LOAD & RELATIVE DAMAGE
CE
E 3
20W
inte
r 20
06
• ServiceabilityServiceability is the ability of a pavement to serve the commuters for the desired results for which it has been constructed within the designed life and without falling the Terminal level (TSI).
• Present Serviceability Index (PSI)Present Serviceability is defined as the adequacy of a section of pavement in its existing condition to serve its intended use.
• Terminal Serviceability Index (TSI)It is defined as that stage of the pavement condition after which it is not acceptable for the road users.
SERVICEABILITY CONCEPT OF PAVEMENT
CE
E 3
20W
inte
r 20
06
• Defined by users (drivers)• Develop methods to relate physical
attributes to driver ratings• Result is usually a numerical scale
From the AASHO Road Test(1956 – 1961)
SERVICEABILITY CONCEPT OF PAVEMENT
CE
E 3
20W
inte
r 20
06
Present Serviceability Index (PSI)
• Values from 0 through 5• Calculated value to match PSR
PCSVPSI 9.01log80.141.5
SV = mean of the slope variance in the two wheel paths (measured with the profile meter)
C, P = measures of cracking and patching in the pavement surface
C = total linear feet of Class 3 and Class 4 cracks per 1000 ft2 of pavement area. A Class 3 crack is defined as opened or spilled (at the surface) to a width of 0.25 in. or more over a distance equal to at least one-half the crack length. A Class 4 is defined as any crack which has been sealed.
P = expressed in terms of ft2 per 1000 ft2 of pavement surfacing.
CE
E 3
20W
inte
r 20
06
PSI vs. Time
Time
Ser
vice
abil
ity
(PS
I) p0
pt
p0 - pt
CE
E 3
20W
inte
r 20
06
Pavement Thickness Design is the determination of thickness of various pavement layers (various paving materials) for a given soil condition and the predicted design traffic in terms of equivalent standard axle load that will provide the desired structural and functional performance over the selected pavement design life i.e. the serviceability may not fall below the TSI.
PAVEMENT THICKNESS DESIGN Comprehensive Definition
CE
E 3
20W
inte
r 20
06
Section - 3
Flexible Pavement Design
CE
E 3
20W
inte
r 20
06
Flexible Pavements
A flexible pavement absorbs the stresses by distributing the traffic wheel loads over much larger area, through the individual layers, until the stress at the subgrade is at an acceptably low level. The traffic loads are transmitted to the subgrade by aggregate to aggregate particle contact. A cone of distributed loads reduces and spreads the stresses to the subgrade.
SHOULDER7.30 m2.00 m 2.00 m
SHOULDERCARRIAGE WAY
cLOF ROAD
A C WEARING COURSE
WATER BOUND MACADAM
SUB BASE COURSE
N.S.L.N.S.L.
2% 4%4% 2%
TYPICAL CROSS-SECTION OF FLEXIBLE PAVEMENT
SUB GRADE / COMMON MATERIAL
COMPACTEDEMBANKMENT
COMPACTEDEMBANKMENT
CE
E 3
20W
inte
r 20
06
Vertical stress
Foundation stress
TYPICAL LOAD & STRESS DISTRIBUTION IN FLEXIBLE PAVEMENTS.
Bituminous Layer
Wheel Load
Sub-grade
CE
E 3
20W
inte
r 20
06
EFFECT OF PAVEMENT THICKNESS ON STRESS DISTRIBUTION
CE
E 3
20W
inte
r 20
06
BASIC EQUATION OF AASHTO PROCEDURE FOR FLEXIBLE PAVEMENT DESIGN.
07.8log32.2
1
109440.0
5.15.4log
20.01log36.9log 10
19.5
10
101810
RoR M
SN
PSI
SNSZW
The various terms/parameters which are used in the basic equation of AASHTO Procedure for the Design of flexible pavements are:
i). W18 (ESAL): It is the accumulated traffic load converted to 18-kips or 8.2 tons. This is also known as 18-kips Equivalent Standard Axle Load (ESAL). That the pavement will experience over its design life.
CE
E 3
20W
inte
r 20
06
ii). Standard Deviation (S0):
Standard deviation accounts for standard variation in materials and construction, the probable variation in traffic prediction and variation in pavement performances for a given design traffic application. The recommended value of S0 for flexible pavement is 0.4 to 0.5.
iii) Reliability (R):
Design Reliability refers to the degree of certainty that a given pavement section will last for the entire design period with the traffic & environmental condition. The recommended level of reliability for freeways in rural areas varies from 80% to 95%. A high reliability value will increase the thickness of pavement layer and will result in expensive construction.
CE
E 3
20W
inte
r 20
06
Recommended Level of Reliability ( R )
Functional Classification
Reliability (%)
Urban Rural
Interstate and Other Freeways 85-99.90 80-99.90
Principal Arterial 80-99 75-95
Feeders 80-95 75-95
Local 50-80 50-80
TABLE FOR REALABLILITY
CE
E 3
20W
inte
r 20
06
iv). Standard Normal Deviate (ZR):
It is defined as the probability that serviceability will be maintained at adequate levels from a user’s point of view throughout the design life of the facility.
This factor estimates the probability that the pavement will perform at or above the TSI level during the design period and it accounts for the inherent uncertainty in design. The relationship of reliabilities with ZR is given in the table:
Value of (ZR)
Reliability R (%)Standard Normal
Deviate (ZR)
50 0.00060 -0.25370 -0.52475 -0.67480 -0.84185 -1.03790 -1.28291 -1.34092 -1.40593 -1.47694 -1.55595 -1.64596 -1.75197 -1.88198 -2.05499 -2.327
99.9 -3.09099.99 -3.750
CE
E 3
20W
inte
r 20
06
v). Structural No (SN):
Structural No is the total structural strength value required to cater for the cumulative equivalent standard axles load (CESAL) during design life so that the serviceability may not fall below the Terminal serviceability Index (TSI)
Definition of Structural Number
Subgrade
Structural Coefficient (a):a = fnc (MR)SN = SN1 + SN2 + SN3
CE
E 3
20W
inte
r 20
06
vi) Loss of Serviceability Index ∆ PSI.
∆ PSI = Initial Serviceability Index – Terminal Serviceability IndexThe recommended value for initial serviceability index is 4.2 while for terminal serviceability index it is to 2 to 2.5.
∆ PSI = 4.2 – 2.5 = 1.7
Time
Serv
iceab
ilit
y (P
SI) p0
pt
p0 - pt
CE
E 3
20W
inte
r 20
06
vii). Resilient Modulus (MR):
It is defined as repetitive or cyclic stress divided by recoverable strain. Resilient Modulus is a measure of stiffness of the soil.
MR = Repetitive stress / recoverable strain MR can be determined from the resilient modules test in the laboratory or from the following equations:MR = 1500 * CBR for CBR < 10 %MR = 2555 (CBR)0.63 for any value of CBR
CE
E 3
20W
inte
r 20
06
viii). Computation of Required Pavement Thicknesses
The structure Number (SN) requirement as determined through adoption of design parameters as discussed above is balanced by providing adequate pavement structure. Under AASHTO design procedure the following equation provides for the means for converting the structural number into actual thickness of surfacing, base and sub base materials.
SN = a1D1 + a2D2m2 + a3D3m3 _______________ (2)
a1, a2, a3 = Layer coefficients representative of surface, base
and subbase courses respectively. It depends upon the modulus of resilient.D1. D2, D3 = Actual thicknesses (in inches) of surface, base and subbase courses respectively.
m2, m3 = Drainage coefficients for base and subbase layers respectively.
CE
E 3
20W
inte
r 20
06
This equation does not have a single unique solution.
There are many combinations of layer thicknesses that can be adopted to achieve a given structural number. There are, however, several design, construction and cost constraints that may be applied to reduce the number of possible layer thicknesses combinations and to avoid the possibility of constructing an impractical design. According to this approach, minimum thickness of each layer is specified to protect the under lying layers from shear deformation.
ix). Recommended Value of Layer Coefficients Asphaltic Wearing Course, a1 = 0.44/inch (0.1732/cm)Asphaltic Base Course, a1 = 0.40/inch (0.1575/cm) Water Bound Macadam, a2 = 0.14/inch (0.0551/cm) Granular Subbase, a3 = 0.11/inch (0.0433/cm)
OR Nomograph can be used to work out SN.
CE
E 3
20W
inte
r 20
06
NOMOGRAPH
CE
E 3
20W
inte
r 20
06
Section - 4
How to Design
CE
E 3
20W
inte
r 20
06
How to Design
Step 1.Fix the design life of the pavement.
Step 2.Work out MR value of the subgrade
MR = 1500 CBR for CBR <10% OR
MR = 2555 (CBR)0.63 for CBR > 10OR
Work out MR in the laboratory.
Step 3.Conduct 7-days traffic count.
Step 4.Classify the traffic and consider the commercial vehicles i.e. Bus, Tractor , Trolley, 2-Axle, 3-Axle, 4-Axle, 5-Axle and 6-Axle Trucks.
Step 5.Take Growth rate from the table on the next slide.
CE
E 3
20W
inte
r 20
06
S. No Vehicle Class Growth Rate
1 Bus 8.4%
2 Tractor Trolley 7.9%
3 Mini Truck 7.9%
4 2-Axle 7.0%
5 3-Axle (Single) 7.0%
6 3-Axle (Tandem) 7.0%
7 4-Axle 7.0%
8 5-Axle 7.0%
9 6-Axle 7.0%
Growth Rate
CE
E 3
20W
inte
r 20
06
S. No Vehicle Class Equivalency Factor (Empty)
Equivalency Factor (Loaded)
1 Bus 0 0.939
2 Tractor Trolley 0.1 1.19
3 Mini Truck 0.0172 2.596
4 2-Axle 0.043 6.49
5 3-Axle (Single) 0.072 16.62
6 3-Axle (Tandem) 0.072 18.48
7 4-Axle 0.206 19.00
8 5-Axle 0.084 19.59
9 6-Axle 0.165 27.96
CONVERT THE TRAFFIC TO EQUIVALENT STANDARD AXLE LOAD.
ESAL = TRAFFIC X EQUILLANCY FACTOR , EQUIVALENCY FACTOR FOR VARIOUS CLASSES OF VEHICLES ARE GIVEN
IN THE FOLLOWING TABLE.
CE
E 3
20W
inte
r 20
06
Vehicle Type ADTAnnual Traffic
Growth Rate %
Growth Factor
Total Traffic for 10 Years
ESA Factor
CESAL for 10 Years
80% 20%
Loaded Empty
Buses 20 7300 6 13.18
96,214 0.939 0
72,276
Tractor Trolly 139 50735 6 13.18
668,687 1.19 0.1
649,964
Trucks2XL 500 182500 6 13.18
2,405,350 6.49 0.043
12,509,263
Trucks 3XL 250 91250 6 13.18 1202675 18.48 0.072
17,797,666
Calculation of CESAL
CE
E 3
20W
inte
r 20
06
Cumulate the future traffic throughout the design life with the help of the selected growth rate. Following is the simple relation to project the traffic to any selected year.
Pn = (1 + r)n – 1 WherePn = Projected traffic for nth year r = Growth rate n = year of consideration
Add all the yearly traffic from base year to the last year of the design life.
CE
E 3
20W
inte
r 20
06
Step 6.Fix the parameter like R, ZR, So, ∆ PSI etc.The generally taken value of the above
parameters is listed below:∆ PSI = 1.7R = 90%So = 0.45ZR = -1.282
Step 7.Put these values in equation 1 and use trial & error method or Nomograph to work out the SN
SN = a1D1+a2D2m2+a3D3m3 Step 8.
Take the value of m2 and m3 from the table on the next slide.
CE
E 3
20W
inte
r 20
06
QUALITY OF DRAINAGE
Quality of Drainage Water Removed within
Excellent 2 hours
Good 1 day
Fair 1 week
Poor 1 month
Very Poor water will not drain
TABLE FOR QULALITY OF DRAINAGE
CE
E 3
20W
inte
r 20
06
Quality of Drainage
Percent of Time Pavement Structure is exposed to Moisture Levels Approaching Saturation
Less Than Greater Than
1% 1 - 5% 2 - 25% 25%
Excellent1.40 - 1.35 1.35 - 1.30 1.30 - 1.20 1.20
Good1.35 - 1.25 1.25 - 1.15 1.15 - 1.00 1.00
Fair1.25 - 1.15 1.15 - 1.05 1.00 - 0.80 0.85
Poor1.15 - 1.05 1.05 - 0.80 0.80 - 0.60 0.60
Very Poor1.05 - 0.95 0.95 - 0.75 0.75 - 0.40 0.40
CE
E 3
20W
inte
r 20
06
Put the above values in equation at step No. 07, to find out the various combination of thicknesses, keeping in view the minimum thicknesses requirements as mentioned below:
– Minimum Asphalt wearing course thickness = 5 Cm
– Minimum asphaltic base course thickness = 7.5 Cm
– Minimum unbound base course thickness = 15 Cm
– Minimum unbound sub base thickness = 15 Cm
Select the most appropriate and economical combination of thicknesses.
CE
E 3
20W
inte
r 20
06
Section - 5
Practical Example
CE
E 3
20W
inte
r 20
06
Practical Example• Let us work out the thicknesses of
various layers for the Pavement of Topi Bypass Road.
1.The ADT is given as follow.Vehicle Type ADT
COASTER/ FLYING COACH 250
BUSSES 25
Tractor Trolley 36
Trucks2XL 110
Trucks 3XL 2
Trucks 4XL 5
CE
E 3
20W
inte
r 20
06
THE CESAL IS WORKED OUT AS FOLLOW:-
Vehicle Type ADTAnnua
l Traffic
Growth
Rate %
Growth Factor
Total Traffic for 10 Years
ESA Factor
ESAL for 10 Years
80% 20%
Loaded Empty
COASTER/FLYING COACH 250 91250 8.4 14.78
1,348,67
5 0.939 0
1,013,125
BUSSES 25 9125 8.4 14.78
134,868 0.939 0
101,312
Tractor Trolly 36 13140 7.9 14.423
189,518 1.19 0.1
184,212
Trucks2XL 110 40150 7 13.82
554,873 6.49 0.043
2,885,673
Trucks 3XL 2 730 7 13.82 10088.6 18.48 0.072
149,295
Trucks 4XL 5 1825 7 13.82 25221.5 19 0.385
385,309
Total 4,718,925ESAL by taking 100 % of directional factor 4718925.35 = 4.719millionESAL by taking 80 % lane factor 3775140.28 = 3.775million
CESAL =3.775 million
CE
E 3
20W
inte
r 20
06
• California Bearing Ratio (CBR)= 30 % at 95% MDD
• MR= 2555 (CBR)0.63 for CBR > 10 Putting the value CBR , MR= 18000 Psi
• Keeping the value of various parameters as follow.
R= 90%So=0.45∆Psi=1.7Using Nomograph to work out the SN
CE
E 3
20W
inte
r 20
06 Required SN = 3.3554
CE
E 3
20W
inte
r 20
06
• Using the following the equation• SN = a1D1+a2D2m2+a3D3m3
• Given Data:•a1=0.44, •a2=0.14 , •a3=0.11 and •m2,m3=1•from Nomograph SN= 3.35
• Putting these values and assuming d1=2 inch, d2=10 inch and d3=10 inch
3.35=0.44*2+0.14*10+0.11*103.35≈3.38
Hence the Design thickness areACWC= 5cmWBM=25cm Granular sub base=25cm
CE
E 3
20W
inte
r 20
06
Thank You
top related