Page 21 - UNIT 5- FLEXIBLE PAVEMENT DESIGN

Civil Engineering Department | DCC3113 : Highway & Traffic Engineering

Sub-grade condition

• In case of varying CBR for 1m depth of sub-grade, mean CBR is determined as follows:

CBR = [(h CBR 1/3 + h CBR 1/3 + … + h CBR 1/3 ) / (1000)]
3
2
2
1
m
n
n
1

Where:
CBR = mean CBR for that location
m
CBR1, CBR2, … CBR = CBR of soil strata
n
h , h , … h = thickness of soil strata (mm)
n
2
1
h + h + … + h = 1000 mm
n
1
2

• A minimum CBR of 5% is recommended for pavements that have to support traffic
volumes corresponding to Traffic Classes T2 through T5.
• For road pavements that designed for large volumes traffic (Traffic Classes T4 and T5), a
minimum sub-grade strength corresponding to CBR of 12% is recommended. For
pavements design purposes, the use of average CBR or sub-grade modulus test results is
not recommended.

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Prepared by : SITI ZURAIFA BINTI MD SAH, zuraifa@pmu.edu.my