Overlay can be of many types:
Characteristic Deflection :
(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:
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=550log10(Dc/Da)
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
