Example 7.8

Design a new flexible pavement for a two lane undivided carriageway using the following data:

Design CBR value of sub-grade = 5.0 %

Initial traffic on completion of construction = 300 cv per day

Average growth rate = 6.0 per year

Design life = 10 years

VDF value = 2.5

Solution

Given data:

r = 5.0 % = 0.05 per year, N = 300 cv per day, F = 2.5, n = 10 years

Lane distribution factor as per IRC recommendation for 2 lane undivided road, D = 0.75.

Vide Wq. 7.15,

$CSA = \frac{365 {NFD[1 + r]^n – 1}}{r}$

Substituting, CSA = 2.7 msa, say 3.0 msa

Using CBR design chart (Fig. 7.14), for CBR = 5% and CSA = 3,

Total design thickness = 530 mm

Composition of pavement components (as per IRC Guidelines):

GSB = 230 mm

GB = 250 mm

BM = 50 mm

PC = 20 mm

Total = 530 mm

Example 7.9

The initial traffic after completion of construction of a four lane divided highway is estimated to be 3500 cv per day. Design the flexible pavement for a life of 15 years using the data given below:

Design CBR value = 8 %, growth rate of cv = 6.5 % p a, Average VDF value of cv = 4.0.

Solution

Given data:

CBR value = 8 %, N = 3500, r = 6.5 % = 0.065, VDF = 4.0, n = 15 years.

Lane distribution factor for 4-lane divided highway as per IRC recommendation, D = 0.75. Vide Wq. 7.15,

$CSA = \frac{365 {NFD[1 + r]^n – 1}}{r}$

Substituting, the values as above = 100.39 msa

Using CBR design chart vide Fig. 7.15, for CBR = 8% and CSA value of 100 msa, total thickness of flexible pavement = 640 mm.

Adopt composition of pavement component’s (as per IRC Guidelines):

GSB = 200 mm

GB = 250 mm

BM = 140 mm

PC = 50 mm

Total = 640 mm