2. (3 points) Determine the overlay thickness for a flexible pavement whose asph

Question

2. (3 points) Determine the overlay thickness for a flexible pavement whose asphalt concrete (AC) layer has a severe degree of alligator cracking (around 35% of the surface), and there is evidence degradation of the granular base and the subbase. The original asphalt layer had a thickness of 4", the base had a thickness of 6", and the subbase had a thickness of 8" Assume that the overlay material will have a structural coefficient of 0.45, and that the structural number required to meet future demands is 4

Explanation / Answer

Given

Alligator Cracking 35% of the surface

Asphalt Layer 4 inch thick 100mm

Base 6 inch 150mm

Sub-base 8 inch 200mm

Structural Coefficient 0.45

Future Demand 4

To find

Overlay Thickness of Flexible Pavement

Solution

Overlay thickness will be,

For Effective thickness for old pavement conversion factor for Asphalt showing 35% is 0.6, for base c.f is 0.5 and bub base c.f is 0.1 C.F here are taken from IS Code so

HOld = 100 x 0.6 + 150 x 0.5 + 200 x 0.1 = 215mm

HNew = 4 x 100 x 0.6 + (150 x 0.45 + 200 x 0.45) = 397.5mm C.F from Given

HOverlay = 397.5 – 215 = 182.5mm

Important to meet future demands thickness for flexible pavements is more so please keep this as a note. Its more than required but to meet expectations design is made as per it also its not economical.

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