Surprisingly Useful AI Article Enhancements
A team of engineers at Monash University is challenging the way Australia designs and builds its underground pipeline networks, arguing that the soil packed around buried pipes should be treated as a frontline defence against corrosion rather than a passive structural filler.
The research, published in Geotechnical and Geological Engineering, explores how specially designed backfill materials could function as an active corrosion protection system for ductile iron pipelines buried across the country.
It is a problem with significant financial implications. Australia manages an estimated 260,000 kilometres of pipelines, roughly 80 per cent of which are buried underground and constructed from metallic materials that are vulnerable to corrosion over time. Corrosion-related failures are estimated to cost up to $1 billion annually through repairs, maintenance, water loss and infrastructure replacement.
The case for rethinking backfill
The review paper draws together research from two traditionally separate disciplines – geotechnical engineering and corrosion science – to examine how factors including moisture content, soil acidity, salt concentration, electrical resistivity and compaction collectively influence the rate at which buried ductile iron pipelines degrade.
At the heart of the argument is a straightforward observation: the soil surrounding a buried pipeline is not neutral. It actively shapes the electrochemical conditions that drive corrosion. Yet in practice, backfill materials have historically been selected for their mechanical properties – the ability to support and stabilise a pipe – with little regard for their electrochemical characteristics.
Lead Author and Monash PhD Candidate, Thisara Senarathna, explained that current industry approaches overlook a critical variable.
“Protective coatings and cathodic protection systems remain important, but their effectiveness is strongly influenced by the surrounding soil conditions,” Mr Senarathna outlined.
“Our work shows backfill should be treated as part of the corrosion protection strategy itself, not just material used to support the pipe.”
A billion-dollar corrosion problem
The scale of Australia’s buried pipeline infrastructure makes the issue difficult to ignore. Many of the country’s water distribution networks were installed during the early twentieth century, and corrosion-related failures have been increasing as these assets age.
According to data cited in the paper, Australia reports an average of 20 cast-iron water pipeline failures per 100 kilometres each year. Since 2006, the cost of replacing corroded pipelines has risen by 10 per cent annually.
Globally, the picture is similar. A significant body of research has identified external corrosion driven by oxygen reduction reactions at the metal-soil interface as the dominant degradation pathway for uncoated or coating-damaged ductile iron pipelines.
The conventional response has been to rely on protective coatings and cathodic protection systems. Coatings create a physical barrier between the pipe and the surrounding soil, while cathodic protection uses electrical current to suppress the electrochemical reactions that cause corrosion.
Both methods have proven effective, but neither is without limitations. Coatings can be damaged during installation, deteriorate over time or be compromised by reactive soil movements. Cathodic protection systems require ongoing monitoring and maintenance, and their performance depends on the conductivity of the surrounding soil.
The compaction paradox
One of the more striking findings outlined in the review relates to the relationship between standard geotechnical compaction practices and corrosion risk.
In civil engineering, backfill soil is typically compacted to achieve maximum dry density, which provides the structural support a pipeline needs. However, the Monash researchers highlight earlier work demonstrating that the moisture content corresponding to maximum compaction also coincides with the conditions under which corrosion rates peak.
Related: Best Business Laptops for work & school
Related: Best Gaming Laptops
Related: Best Portable Laptop
The review cites research showing that when soil is compacted to its optimum moisture content, both electrical conductivity and oxygen diffusion reach levels that create an ideal environment for electrochemical corrosion. In sand, peak corrosion activity occurs at a degree of saturation of approximately 0.5. In silt, it occurs at around 0.7. In clay, at approximately 0.8.
This creates what the researchers describe as an unintended consequence of standard geotechnical practice: optimising soil compaction for structural stability inadvertently provides ideal conditions for pipeline corrosion.
How soil properties drive corrosion
The review provides a detailed analysis of the individual soil parameters that influence corrosion rates.
Soil resistivity is a key indicator. Soils with resistivity values below 1,000 ohm centimetres are classified as highly corrosive, while those above 2,000 ohm centimetres are considered non-corrosive. Fine-grained materials like clay have the lowest resistivity due to ionic conductivity, while coarse materials like gravel and river sand offer higher resistivity and lower corrosion risk.
Moisture content plays a dual role. As soil moisture increases, electrical conductivity improves, which accelerates corrosion by enabling electrochemical reactions. But higher moisture levels also displace air within the soil, reducing the amount of oxygen that can reach the metal surface. This creates a tipping point – an optimum moisture level where corrosion is at its worst.
Soil pH, particle size distribution, stray electrical currents from nearby infrastructure and microbial activity in the soil all contribute as well. The review notes that sulphate-reducing bacteria, which thrive in saturated, low-oxygen conditions, can generate hydrogen sulphide that destabilises protective corrosion products on pipe surfaces.
Engineered backfill as a solution
The core proposition of the research is that backfill materials can be engineered to control the electrochemical environment surrounding a buried pipeline.
The ideal backfill, according to the review, would maintain a low degree of saturation under local climatic conditions, drain freely at pipe level, exhibit high electrical resistivity and provide sufficient stiffness for structural support.
These properties can be achieved by modifying the gradation of backfill materials and their water retention characteristics. The researchers describe a “capillary break” concept in which a coarse-grained backfill with low water retention is placed adjacent to finer-grained surrounding soil, creating a discontinuity in moisture movement that keeps the area around the pipe drier.
The review also explores the potential for recycled materials to serve as backfill. Crushed concrete, crumb rubber from end-of-life tyres and crushed glass have all shown promise in modifying the hydraulic and electrical properties of backfill soils. Their use would also support waste reduction and circular economy objectives.
However, the researchers caution that the relationship between recycled material composition and actual corrosion performance has not yet been quantitatively validated, representing a gap that future studies will need to address.
Australian industry survey reveals gaps
The paper includes results from an industry survey conducted by the Monash team in collaboration with the Water Services Association of Australia (WSAA), which represents utilities providing water and wastewater services to more than 24 million customers.
The survey collected 54 responses from professionals across all six Australian states and territories working in pipeline design, asset management and operations.
The results are revealing. Inadequate cathodic protection was the most commonly reported issue, identified by 65 per cent of respondents as a major concern. Nearly half of respondents highlighted problems related to moisture dynamics and extreme soil pH. Electrical interference was flagged by 35 per cent of organisations, while 24 per cent reported challenges with stray currents.
When it came to remedial measures, enhanced cathodic protection was the most widely employed solution at 65 per cent, followed by regular inspections and monitoring at 53 per cent. Engineered backfill materials were notably underutilised, with only 18 per cent of respondents indicating their use.
The survey also found no standardised maintenance timeline across the industry. Half of the surveyed professionals favoured performance-based maintenance, where intervention is triggered by observed issues rather than fixed schedules. A further 36 per cent recommended inspection intervals of four to five years, while 14 per cent suggested every 10 years.
A call for integrated design
Co-Author, Professor Jayantha Kodikara, Director of the ARC Smart Pavements Hub at Monash, argued the findings support a shift in how the industry approaches pipeline infrastructure.
“Corrosion is often treated as a separate issue from geotechnical engineering, but these systems are deeply interconnected,” Professor Kodikara noted.
“This research highlights the need for more integrated infrastructure design approaches that consider both structural performance and long-term corrosion resistance.”
The broader research project at Monash is investigating new resistive backfill materials, construction methods and modelling techniques aimed at minimising corrosion across entire pipeline networks. That includes examining interference effects between adjacent buried pipes in congested urban environments, where the proximity of multiple metallic structures can complicate corrosion dynamics.
Cost and sustainability implications
The researchers argue that the approach could offer a more practical and lower-cost pathway for improving infrastructure longevity compared to reactive maintenance and replacement strategies.
The review notes that shorter maintenance intervals translate directly to higher operational costs, including labour, materials and potential service disruptions. Pipelines buried in highly corrosive soils may require maintenance within less than four years, according to the survey respondents.
By contrast, engineered backfill that controls the electrochemical environment around a pipe from the point of installation could reduce the frequency of maintenance interventions over the asset’s lifetime. The approach is described as a passive, low-maintenance mitigation strategy that complements rather than replaces existing coating and cathodic protection systems.
There are sustainability dimensions as well. Replacing corroded pipelines carries a significant carbon footprint through material extraction, manufacturing and construction. Extending the service life of existing assets through better backfill design aligns with broader carbon-reduction goals in civil infrastructure.
The use of recycled construction and demolition waste as backfill material would also divert waste from landfill and reduce dependence on quarried aggregates.
Barriers to adoption
Despite the potential benefits, the survey results suggest that uptake of engineered backfill remains low. Key constraints identified by respondents include higher costs relative to conventional materials, a lack of standards and guidelines, and construction-related technical challenges such as stricter compaction control and material verification requirements.
The researchers recommend the development of unified performance-based standards for engineered backfill materials, the incorporation of lifecycle cost assessment frameworks into procurement processes and targeted professional training programs within the water utility sector.
The review paper represents a synthesis of existing knowledge from both geotechnical engineering and materials science, combined with practical insights from Australian industry professionals. The researchers position it as a foundation for moving from conceptual recommendations to field-level implementation.
The research was supported by the Australian Research Council Discovery Project and the Water Services Association of Australia. The study involved researchers from Monash University, James Cook University and the University of British Columbia.
Last Updated on May 18, 2026 by Nick Ross
