1. Analyse Solve Construct
Recycle Manufacture Blend
“A temporary alignment plus a
staged paving sequence allowed
for 95% of surfacing to completed
in one sequence, minimizing joins.
Tandem paving eliminated any
longitudinal joins.”
The Tatuanui junction has heavy traffic loadings with B
Train trucks travelling day and night en-route between
Auckland and Rotorua/Taupo. The existing intersection
was a staggered “T” which often caused significant
queuing, poor driving decisions and resulted in a high
accident rate. The eastbound and westbound traffic often
delayed northbound and southbound traffic causing
frustration and erratic movements. The construction of a
new roundabout has improved both traffic flow and safety
to this section of the state highway network.
Client New Zealand Transport Agency
Consultant AECOM
Principal Contractor J Swap Contractors Limited
State Highway 26/27 Tatuanui
Roundabout and Passing Lane
– constructing an intersection that will withstand
high volume, heavy and oversized traffic loads
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2. The project team developed a sequencing
plan; the resulting staging of works critical
in maintaining the flow of traffic on the
state highway, and reducing the project’s
impact on the railway line.
An innovative methodology was developed to address the
high stress and loadings on the pavement and proportion
of heavy commercial vehicles through the intersection.
A ‘Hi-Lab” pavement base was constructed comprising
a cement stabilized basecpurse designed for the project.
To further strengthen the pavement a durable multi-layer
AC14 NAS (with a HPSV) surface course was constructed.
This was developed as an alternative to using Stone Mastic
Asphalt (SMA) which had demonstrated limited surface life
on other similarly trafficked roundabouts.
The AC 14 design was devised with a 14mm stone, Grade
3/5 chip and PAP. It is a denser graded mix, impervious
compared to SMA, and has greater strength and service life
in situations such as this. The denser mix design has the
advantage of being less prone to oxidation of bitumen, and
exhibiting stronger resistance to shear stresses under heavy
traffic. This is expected to translate to a design life of 20 –
25 years as opposed to 8 – 10 years with SMA.
Asphaltic paving was completed in two lifts, to achieve
structural strength and improved surface ride quality –
one 40mm layer of AC 14 NAS followed by a second
35mm AC20 NAS was used beside the railway lines to
accommodate loadings and vibrations from rail operations.
The paving sequence developed ensured there were minimal
surface joints. This was very important due to the heavy and
light turning nature of traffic loading on the roundabout.
Traffic volumes 10,000 vehicles per day
Asphalt cartage time to site 75 minutes
Asphalt lay rate 30 tonnes per hour
Mix Design
40mm layer of AC14 NAS
35mm layer of AC 14 NAS
There were multiple constraints with the project sequencing.
Advanced planning was required for asphalt manufacture
and transportation; a 75 minute cartage time to the site
had to be factored in. Blacktop Construction drew up a
detailed batching and cartage schedule to establish a set
and predictable delivery of product to the site. This allowed
consistent operation of paving and compaction plant on site,
improving ride and joint quality throughout.
The resultant finished ride was exceptional, and with the
project constructed within an accelerated timeframe, this
earned the project an overall PACE scores of 84/100.
Railw
ay
Lines
A
D
E
F
CB
A
BLACKTOPGROUPBLACKTOPGROUP
“A ‘customer first’ approach
was adopted to ensure traffic
on this critical route flowed and
experienced minimal delays.”
A Day 1 AC 14NAS/40mm
B Day 1a
AC 20NAS
variable thickness
C Day 2a
AC 20NAS
variable thickness
D
Day2 AC 14NAS/40mm
Day 3 AC 14NAS/35mm
E
Day 1 AC 14NAS/40mm
Day 3 AC 14NAS/35mm
F
Day 4 AC 14NAS/40mm
Day 4a AC 14NAS/50mm
NOTE
1 Day 1 = Paved 1st layer (40mm AC 14NAS)
1a Day 1 = Paved AC 20NAS (Variable Depth)
2a Day 2 = Paved AC 20NAS (Variable Depth)
2 Day 2 = Paved 1st layer (40mm AC 14NAS)
3 Day 3 = Paved final layer (35mm AC 14NAS)
4 Day 4 = Paved 1st layer (40mm AC 14NAS)
4a Day 4 = Final layer at last stage