You will need to provide six pavement design options for the bypass, including four options of an unbound pavement with thin bituminous surfacing and two options of an asphalt pavement. The pavement structure is to be constructed for a design life of 25 years. Current AADT (in 2021) is 4500. The bypass is scheduled to open in 2022. Project reliability is 95%. The traffic load distribution (TLD) is provided in the Pavement Design Data Excel file on LMS. The following parameters must be used:
• Heavy vehicles = 8%, annual vehicle growth rate = 6%, and Subgrade CBR = 6 (elastic modulus E = 60 MPa and Poisson’sratio ν = 0.45).
Three materials are available for flexible pavement construction:
• Good quality crushed rock with CBR = 81 (elastic modulus E = 810 MPa and Poisson’s ratio ν = 0.35)
• Marginal gravel material with CBR = 40 (elastic modulus E = 400 MPa and Poisson’s ratio ν = 0.35)
• Hot mix asphalt with 10% bitumen (by volume), elastic modulus E = 2200 MPa and Poisson’s ratio ν = 0.4
The following questions must be addressed:
a) Compute the design traffic (NDT) for pavement design.
b) Compute the design number of ESAs (DESA) applicable to a flexible pavement.
c) Work out design solutions for the unbound pavement with thin bituminous surfacing:
• Two structures: one containing only crushed rock base and the other containing a crushed rock base and a marginal gravel sub-base.
• Two conditions of the subgrade materials: subgrade material in its natural state and subgrade material stabilised with 6% lime.
• There will be four unbound pavement design options altogether (crushed rock + subgrade; crushed rock + marginal gravel + subgrade; crushed rock + subgrade with 6% lime; and crushed rock + marginal gravel + subgrade with 6% lime)