Question

It is proposed to widen an existing 2-lane nh section into 4-lane divided road. Design the pavement; 4-lane divided carriageway (2 lane in each direction); initial traffic in each directions in the year of completion of construction = 5600 commercial vehicles/day; design life = 10 years; design cbr value of sub-grade = 5%; vdf = 4.5; assume traffic growth rate = 8% (from records).​

Answer 1

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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=365NFD[1+r]n–1r

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

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