In this project, your company has been contracted by VicRoads 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 Austroads Guide to Pavement Technology 2017.
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 2019) is
4200. The bypass is scheduled to open in 2020. 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:
• Heavy vehicles = 10%, annual vehicle growth rate = 3%, and Subgrade CBR = 5 (elastic modulus E = 50 MPa and Poisson’s ratio = 0.45).
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 = 35 (elastic modulus E = 350 MPa and Poisson’s ratio = 0.35)
• Hot mix asphalt with 15% bitumen (by volume), elastic modulus E = 2700 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. Note: the unbound pavement designs must be carried out using the empirical design approach.
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 between 100mm and 300mm. There will be two asphalt pavement design options altogether. Note: the asphalt pavement designs must be carried out using the mechanistic design approach (i.e. CIRCLY).
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 economic design and draw a sketch giving full details of the design dimensions and parameters.
g) Discuss the environmental impacts of the unbound and asphalt pavements in general and recommend methods to reduce these environmental impacts, with relevant supporting references.
Prepare a report of your preliminary designs and recommendation, which should be structured as shown in Table 1.