Bridge No. 1856 spans Pinjarra Williams Road near Boddington in Western Australia’s southwest as part of the South32 Quindanning Mine Enabling Infrastructure project. Supporting a key transport route for the mining operation, the structure is one of the largest precast concrete arch bridges constructed in the Southern Hemisphere.
The bridge has an internal span of 21 metres and a total tunnel length of approximately 36.8 metres. It was designed to support significant fill above the structure and accommodate heavy mining vehicles exceeding 350 tonnes. The bridge is complemented by Geoquest designed and supplied Reinforced Earth walls with precast concrete facing panels at either end.
Infrastructure of this scale demands structural systems capable of managing extreme loads while maintaining reliability over decades of continuous operation.
Designing infrastructure for extreme loading
Mining transport infrastructure is subject to extreme loading conditions, including heavy live loads, deep fill and continuous vehicle traffic. For Bridge No. 1856, the design required a structure capable of supporting both significant permanent loading and repetitive heavy haul vehicles.
A minimum of two metres of cover was provided above the arch, creating substantial vertical loading. At the same time, the structure needed to deliver long term durability while allowing construction to proceed efficiently within an active mining environment.
These conditions required a structural solution capable of providing high load capacity while supporting efficient construction and minimal disruption to the surrounding transport corridor.
Harnessing arch geometry for structural efficiency
The arch units were designed and manufactured by National Precast member and Master Precaster Geoquest Australia using its patented TechSpan precast concrete arch system.
The arch form transfers loads primarily through compression rather than bending, allowing the structure to perform efficiently under heavy fill conditions.
The arch profile follows the geometry of the funicular curve, aligning the structure with the natural load path created by soil pressure and live loading. By directing forces along the curve of the arch, tensile stresses in the concrete are reduced and structural efficiency is improved.
Engineered backfill surrounding the structure forms an important component of the system behaviour. Soil structure interaction distributes loads across the arch and contributes to the long term stability of the bridge.
TechSpan arch systems are designed to accommodate high fills, heavy live loads and the alternating stresses experienced during both installation and long term operation.
Delivering the structure on site
The bridge was installed by contractor Georgiou using a modular precast construction approach that significantly reduced on site construction time.
A total of 48 precast segments were manufactured under controlled factory conditions before being transported to site. The segments were then lifted into position using cranes and installed in a carefully sequenced construction process.
Installation of the arch structure was completed in just two days. The modular precast approach allowed the bridge to be assembled quickly while maintaining construction safety and minimising disruption to the surrounding road network.
Factory production ensured consistent dimensional accuracy and quality control while reducing site based construction work.
“Delivering a structure of this scale in such a short timeframe reflects the capability and reliability of precast solutions,” said Rhys Senior, WA Regional Manager at Geoquest. “It also highlights how innovation and teamwork can redefine what’s possible in mining infrastructure.”
Engineering verification under changing site conditions
During construction, site access constraints meant that different backfill materials had to be sourced for each side of the arch. This created an unbalanced soil density condition across the structure.
Because the precast units had already been manufactured, the project team undertook additional engineering analysis to confirm that the structure could safely accommodate the revised loading environment.
A finite element method model was developed to evaluate alternative backfill materials sourced from nearby borrow pits. Two options were analysed, one heavier than the original design assumption and one lighter.
The heavier option would have required a cement stabilised zone and increased construction cost. The lighter material was ultimately selected as it maintained acceptable structural performance without requiring modification to the precast elements.
The analysis confirmed that the original arch units could remain in place while safely accommodating the revised ground conditions.
By Cadell Taye, CEO National Precast Association
Delivering durable mining infrastructure
TechSpan precast concrete arch systems are designed for long service life infrastructure applications. Depending on project specific exposure conditions and design requirements, installations typically target durability outcomes of up to 100 years.
For the Quindanning Mine project, the combination of arch geometry, engineering analysis and prefabricated construction enabled the rapid delivery of a bridge capable of supporting one of the most demanding transport environments in mining infrastructure.
More broadly, the project demonstrates how precast arch systems can deliver efficient and durable solutions for mining transport infrastructure, particularly where high loads, challenging ground conditions and tight construction programs must be carefully balanced.
Technical summary
Project: South32 Quindanning Mine Enabling Infrastructure
Structure: Bridge No. 1856 over Pinjarra Williams Road
Internal span: 21 m
Total length: 36.8 m
System: Precast concrete arch
Minimum cover: 2 m
Loading: Heavy mining vehicles exceeding 350 tonnes
Units installed: 48 (24 male / 24 female)
Principal contractor: Georgiou
Installation duration: 2 days