GRP pipeline dives deep to decant smarter not harder powering tailings drainage with strength smarts and sensor-backed confidence

When mining operators are faced with the challenge of dewatering a live tailings storage facility (TSF) under 30 metres of cover, conventional engineering approaches often buckle under pressure - literally and figuratively. But a recent project led by Leis Day, principal engineer at Red Earth Engineering - A Geosyntec Company, has demonstrated how a performance-based design underpinned by finite element analysis (FEA) and smart instrumentation can deliver a safe, cost-effective solution using glass-reinforced plastic (GRP) pipelines.

Presented at the Life of Mine - Mine Waste and Tailings 2025 conference in Brisbane, Leis shared a detailed case study on the implementation of a gravity decant system retrofitted into an operational TSF. The paper was co-authored by Chao Han, Wade Ludlow, and Oliver Dudley, also of Red Earth Engineering, and highlights both the engineering rigour and the innovation underpinning the project.

A challenge buried 30 metres deep

The TSF in question was not a greenfield site - it was an operational facility with up to 10 metres of deposited tailings already in place. With additional dewatering capacity needed to support effective mud farming, particularly during the wet season, the operator needed a system capable of handling up to 30,000 cubic metres of water per hour.

Critically, alignments for the decant system were heavily constrained. “We were essentially retrofitting the system into an active facility, so the pipeline alignments had to hug the original starter embankment,” said Leis during his presentation.

That choice, while practical, introduced significant overburden. In some locations, the pipeline would be buried beneath 30 metres of tailings and embankment fill - far exceeding the 10-metre burial depth threshold where AS2566.1 becomes increasingly conservative and less applicable.

Designing outside the standard

Recognising the limitations of a purely code-based approach, Leis and the team adopted a hybrid design strategy. The backbone of the pipeline was GRP, chosen through a rigorous two-stage material selection process.

“GRP gave us the best performance in terms of long-term durability, corrosion resistance, and importantly, cost,” said Leis.

“Compared to reinforced concrete, the GRP procurement cost was about a quarter, largely due to logistics and the ability to nest pipes and deliver them in larger segments.”

With the material selected, the focus turned to structural validation. The team conducted both 2D and 3D FEA to simulate pipe–soil interaction under site-specific ground conditions and load scenarios. The 2D model checked pipe performance against backfill and native soil stiffnesses, while the 3D model focused on axial loads, deflection, and differential settlement across jointed segments.

“Our goal was to determine whether the pipe could handle combined actions - bending, rotation, and elongation - without risking joint pull-apart or excessive strain,” Leis explained.

From modelling to monitoring

The results showed that the GRP pipeline performed well within design limits, even under conservative assumptions. The design factored in joint movement mechanisms, including:

• Pipe elongation up to 10 mm per 12 m segment
• Joint rotation due to differential settlement, capped at 0.35 degrees
• Combined joint movement well within the 36 mm tolerance specified by the manufacturer

But design assurance didn’t end at the model.

In a move that elevates this case study from good practice to leading practice, the team implemented a Distributed Fibre Optic Sensing (DFOS) network along the entire length of the pipeline. This system enables continuous, real-time monitoring of:

• Temperature (to detect seepage or anomalies)
• Strain (to monitor pipe and embankment deformation)
• Acoustic signals (to assess liquefaction risks and internal erosion)

“The DFOS system gives us a continuous feedback loop. It’s not just a snapshot - it’s a live health check on the system's performance,” said Leis.

Conventional instruments such as piezometers and thermistors were also installed to validate and cross-check the DFOS data.

Engineering for buildability

While the analysis and design were advanced, practicality on site was never overlooked. GRP’s lightweight nature - while advantageous for logistics - introduced unique challenges in flotation control and joint pressure testing during construction.

“We knew GRP could float during installation, so anti-flotation design was critical. We also had to plan out the sequence of pressure testing carefully because internal joints can be tricky,” said Leis.

The construction methodology was tailored in consultation with site personnel to ensure safe and efficient trenching, bedding, and backfilling procedures, especially in areas with steep cover or constrained access.

Addressing risk, retaining flexibility

One of the most contentious decisions in TSF design today is whether to introduce pipeline penetrations through the perimeter embankment - especially in retrofit scenarios.

Leis acknowledged this concern directly: “We were asked why we’d opt for a gravity system with an embankment penetration given the known risks of collapse. The answer is capacity. We couldn’t afford a three-month drawdown post-wet season, and the gravity system gives us the volume throughput we need.”

To mitigate risk, the design included double sand and gravel filters, each seven metres square, enveloping the pipeline at the embankment interface to prevent piping and erosion.

“We're not blind to the risks,” Leis emphasised. “We engineered around them.”

Lessons for the broader industry

While this case study focuses on a single site, its lessons are widely applicable. In particular, it demonstrates that:

• GRP is a viable and potentially superior material for deep-buried TSF infrastructure
• A performance-based design, anchored in FEA, provides better certainty and efficiency than conservative standard-based methods alone
• Integrated instrumentation systems like DFOS can transform pipeline monitoring and maintenance strategies
• Early contractor involvement improves buildability and lowers lifecycle risk

As mining operations contend with increasingly complex TSF conditions and regulatory scrutiny, examples like this raise the bar for what’s possible when design is driven by both engineering rigour and site practicality.

Acknowledging the team

Leis credited the broader project team for the successful delivery, including co-authors Chao Han, Wade Ludlow, and Oliver Dudley. “This was a true collaboration between disciplines - geotechnical, structural, hydraulic and construction teams all had to align to make it work.”

Looking forward

With the pipeline now fully implemented and operational, the project stands as a benchmark for future GRP installations in tailings infrastructure. “We hope it provides a reference point for others facing similar challenges,” Leis concluded. “We didn’t follow the path of least resistance - we engineered a system that works for the long haul.”