Saturday, August 10, 2013

Highway Maintenance -Overlay Design

Overlay can be of many types:
(1) flexible overlay over a exiting flexible pavement
(2) flexible overlay over a rigid pavement.
(3) Rigid overlay  over a flexible pavement.
(4) Rigid overlay over a rigid pavement.

(1) Flexible overlay over flexible pavement by convention method of design:

h0 = hd - he
ho= thickness of the flexible overlay over flexible pavement .
hd= Design thickness of the flexible pavement
he= thickness of the existing pavement.

Analysis of Data:

Standard deviation of deflection:

Characteristic Deflection :

Overlay Thickness Design: 

ho= R/0.343 log10(Dc/Da)    ....Ruiz's equation.
ho= Thickness of bituminous overlay in cm.
R= Deflection reduction factor depending on the overlay material

As per IRC: 

ho= Thickness of granular or WBM overlay in mm.
D = D(mean) +6, after applying the correction for the pavement temperature and sub grade moisture.
Da= 1.00, 1.25 & 1.50mm if the projected design traffic A is 1500 to 4500, 450 to 1500 & 150 to 450 respectively.

Rigid Overlay over Rigid Pavement:

Flexible overlay over Rigid Pavement:

hf =2.5(Fhd - he)
where, hf= Flexible overlay thickness
            he= Existing rigid pavement thickness
            hd= Design thickness of rigid pavement
     f= Factor which depend upon modulus of existing pavement.
hb= 1.66(Fhd - he)
where, hb= thickness of the bituminous overlay

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