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GEOTECHNICAL ENGINEERING – SP5
Pavement Design (Marks: 14% of course total)
Due 5.00 pm, 31 October 2022
Part 1 – Calculating Design Traffic
A section of road pavement (somewhere) in Adelaide is to be designed. The design life is 27
years and expected traffic growth rate is 2.79% per year. Limited traffic survey data available
for that particular section of the road (see Table 1).
1A. Using the information in Table 1, calculate AADT and %HV.
Table 1: Site specific survey data
Road type 4 lane 2 way (2 lanes in each direction)
Speed limit 90 km/hour
Road gradient 2.9%
Lane surveyed All (both directions)
Survey duration 19 days
Total number of vehicles counted 21000 + sum of last digit of student ID × 100
Total number of heavy vehicles 7350 + sum of last digit of student ID
Since the survey data was very limited, a decision was made to use TLD (WIM survey data)
from a nearby road with similar traffic characteristics. These data (different for different group)
are presented in a separate spreadsheet file.
1B. From the TLD for your group, calculate NHVAG and ESA/HVAG.
1C. Using the calculated AADT, %HV, NHVAG and ESA/ HVAG, calculate the design traffic
(NDT and DESA) for the road to be designed.
Part 2 – Pavement Design Empirical method (CBR chart)
Assume the subgrade on the site is natural clay with CBR given by the following equation
Design subgrade CBR = 2.5 + sum of student ID last digits × 0.3 (1)
2A. Design a granular pavement (with thin bituminous seal) for the calculated design traffic
in 1C. Present a sketch with all layer and sublayer (lift) thicknesses and material
properties (CBR values) clearly labelled.
2B. Recalculate the thicknesses of pavement layers for a case where in-situ stabilization was
used and subgrade CBR was improved by 25% (multiplier of 1.25 with design CBR in
equation 1).
Note: Layer thicknesses are to be within practical limits for compaction and expressed to the
nearest +10 mm for the base and +20 mm for the subbase. More than one lift thicknesses
(named as upper and lower sub-base) should be used if the subbase thickness is to be greater
than 250 mm.
Part 3 – Pavement design using Mechanistic-Empirical method (CIRCLY)
Using the design traffic calculated in Part 1 and CBR values from equation (1), find 3
alternative workable pavement designs as below. Assume a project reliability of 97.5%.
3a. Granular pavement with thin spray seal
3b. Pavement with asphalt layers
3c. Pavement with a CTCR layer
Perform a cost analysis for each pavement design (use the supplied template for the calculation
and compare it with cost calculated by CIRCLY). Select the pavement configuration you would
prefer (for construction) giving reasons for your choice. Only the materials presented in table
2 to 5 below can be used in your design.
Table 2. Material properties and cost chart for Asphalt
Asphalt Application In service
voids
Laboratory
voids
Binder
volume
Ev (40ms
rise time,
250C)
Cost
AC10M Wearing
course 25-50 mm
5.7% 5% 11.5% 3350 MPa $210 / t*
AC14M Levelling and
intermediate
courses
35-75 mm
5.8% 5% 10.7% 3500 MPa $195 / t*
AC20M Base course(s) 50-
100 mm
5.5% 5% 10.5% 3750 MPa $165 / t*
*Density of asphalt material is 2.5t/m3
Table 3: Material properties of unbound granular materials and
Unbound granular materials Compaction level, RD (%)
[MDD = 2.1 t/m3
]
Ev or Mr (MPa) Cost
PM1/20 (base course) 98 400 – 550* $35 / t
PM2/20 (subbase) 96 250 – 300* $26 / t
PM3/20 (subbase/ working platform) 95 150 – 200* $21 / t
*For design pick any number within this range.
Table 4: Properties and cost for CTCR
Table 5: Cost for Spray seal surfacing
For the pavement with asphalt layer (design 3b) show the calculation (in a spreadsheet) for
CDF (only for layer with highest CDF). Use the calculated strain under SAST and SADT from
CIRCLY output file and other related values (ie, TLD, SF, RF values, constants and
exponents). You can use the supplied template. The template may have some equations
removed and you will have to key them in.
Part 4 – Pavement design using Mechanistic-Empirical method (CIRCLY)
4. Re-design the pavement with asphalt layer (3b) for the following cases and discuss your
observations in the report.
a. Subgrade design modulus is given by the formula: Mr = Ev = 17.6(CBR)
0.64
b. Subgrade layer is 2 m thick and rests on a rock layer

CTCR Application Flexural
strength
(MPa)
Ev or Mr
(MPa)
Cost
SPM2/20QGC4 (4% CTCR) Base course 1.10 3,300 $130 / m3
Spray seal Application Cost
Spray seal including priming Surfacing for granular pavements $18.50/ m2