Flexible Pavement Thickness Design (Aastho method)
Transcript of Flexible Pavement Thickness Design (Aastho method)
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8/13/2019 Flexible Pavement Thickness Design (Aastho method)
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FLEXIBLE PAVEMENT THICKNESS DESIGN
AASHTO METHOD
Example
Determine the thickness of the surface, base and subbase layers using the following
design parameters:
Equivalent Single Axle Load (ESAL) = 2 106
Initial Present Serviceability Index, PSIi= 4.5
Terminal Present Serviceability Index, PSIt= 2.5
Resilient modulus of asphalt concrete, MR1= 450,000 psi
CBR of crushed stone base = 100%
CBR of gravel subbase = 22%
CBR of subgrade = 6%
Exposure to moisture = 30% of the timeQuality of drainage: Surface layer Good
Base layer Fair
Subbase layer Fairly poor
Reliability, R = 99%
Standard deviation, So= 0.35
Solution
(1) Design Serviceability Loss, PSI
PSI = PSIt PSIi = 4.5 2.5 = 2.0
(2) Resilient Modulus
Subgrade : MR4= 6,800 psi (Figure 16-4 Appendix A-4, with CBR = 6%)
Subbase : MR3= 13,300 psi (Figure 16-16, Appendix A-10, with CBR = 22%)
Base : MR2= 30,000 psi (Figure 16-15, Appendix A-9, with CBR = 100%)
(3) Structural Number
(Use nomograph in Figure 16-11, Appendix A-5)
Surface : SN1= 3.2 (with R = 99%, S = 0.35, ESAL = 2 106, and
MR2= 30 103)
Base : SN2= 4.2 (with R = 99%, S = 0.35, ESAL = 2 106, and
MR3= 13 103)
Subbase : SN3= 5.2 (with R = 99%, S = 0.35, ESAL = 2 106, and
MR4= 6.8 103)
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(4) Structural Coefficient
Surface : a1= 0.44 (Figure 16-13, Appendix A-7 with MR1= 450,000 psi)
Base : a2= 0.14 (Figure 16-15, Appendix A-9, with CBR = 100%)
Subbase : a3= 0.098 (Figure 16-16, Appendix A-10, with CBR = 22%)
(5) Drainage Coefficient
(Use Table 16-5, Appendix A-11)
Surface : m1= 1.00 (with moisture exposure > 25% and drainage
quality = good)
Base : m2= 0.80 (with moisture exposure > 25% and drainage
quality = fair)
Subbase : m3= 0.70 (with moisture exposure > 25% and drainage
quality = fairly poor)
(6) SURFACE THICKNESS
27.7)00.1(44.0
2.3
ma
SND
11
11 === in 7.5 in
SN1* = a1D1m1 = 0.44 (7.5) (1.00) = 3.3
SN1* SN1 OK!
(7) BASE THICKNESS
=
=
=)80.0(14.0
3.32.4
ma
*SNSND
22
122 8.04 in 8.5 in
SN2* = a2D2m2 = 0.14 (8.5) (0.80) = 0.95
SN1* + SN2* = 3.3 + 0.95 = 4.25
SN1* + SN2* SN2 OK!
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(8) SUBBASE THICKNESS
=
=
=)70.0(098.0
3.395.02.5
ma
*SN*SNSND
33
1233 13.85 in 14 in
SN3* = a3D3m3 = 0.098 (14) (0.70) = 0.96
SN1* + SN2* + SN3* = 3.3 + 0.95 + 0.96 = 5.21
SN1* + SN2* + SN3* SN3 OK!
(9) PAVEMENT LAYER PROFILE
Surface a1= 0.44 , m1= 1.00 7.5 in
MR1= 450,000 psi
Base a2= 0.14 , m2= 0.80 8.5 in
MR2= 30,000 psi
Subbase a3= 0.098 , m3= 0.70 14 inMR3= 13,300 psi
Subgrade MR4= 6,800 psi
(1 inch = 25.4 mm , 1 psi = 6894.76 Pa)
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