Assignment Task
In this project, your company has been contracted by the Department of Transport and Planning to design a two-lane two-way bypass for a rural town. Your task in this project is to cover road pavement design for the bypass. The pavement design must comply with the Austroads Guide to Pavement Technology.
You will need to provide six pavement design options for the bypass, including four options of unbound pavement with thin bituminous surfacing and two options of asphalt pavement.
The pavement structure is to be constructed for a design life of 20 years. The current AADT (in 2024) is 5750. The bypass is scheduled to open in 2025. Project reliability is 95%. The traffic load distribution (TLD) is provided in the Pavement Design Data Excel file on LMS. Depending on your student ID, the following parameters must be used:
Three materials are available for flexible pavement construction:
- Good quality crushed rock with CBR = 80 (elastic modulus E = 800 MPa and Poisson’s ratio = 0.35)
- Marginal gravel material with CBR = 29 (elastic modulus E = 290 MPa and Poisson’s ratio = 0.35)
- Hot mix asphalt with 10.5% bitumen (by volume), elastic modulus E = 2400 MPa and Poisson’s ratio = 0.4
Note that the above subgrade CBR is the value in its natural state. There is an available option for subgrade CBR improvement. When the subgrade material stabilised with 6% lime, the design CBR was found to increase by 3 (elastic modulus E increases by 30 MPa and Poisson’s ratio remains constant).
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)
d) Work out optimum design solutions for the asphalt pavement, containing asphalt base and a marginal gravel sub-base, for the two conditions of the subgrade materials (subgrade material in its natural state and subgrade material stabilised with 6% lime). The thickness of each pavement layer must be at least 100mm
e) For six pavement designs obtained from (c) and (d), calculate total cost per m2 of pavement and plot a graph comparing the cost of these designs. Pavement costs apply to the materials and construction are included in the Pavement Design Data Excel file. f) Based on the cost calculation in (e), find the most economical design and draw a sketch that gives full details of the design dimensions and parameters.
