Hidden beneath a Newport street, ground movement was quietly destabilising both a home and a council laneway. What looked like a surface issue quickly revealed deeper subsurface failure driven by legacy fill, ageing services and water ingress.
In established urban areas, some of the most significant infrastructure risks are hidden below ground, where ageing assets and legacy construction practices can quietly undermine stability.
Dr Philip Irwin, Business Development Manager at Rectify Group, a leading provider of chemical underpinning, ground engineering and asset remediation solutions, said that ground instability is becoming more common in older suburbs, driven by ageing infrastructure, historical fill materials and environmental factors.
Rectify Group specialises in engineered ground improvement solutions for complex sites, partnering with councils to deliver safe, efficient, and long-term outcomes.
“Many assets were built on poorly compacted fill or legacy materials that do not meet modern standards,” Irwin said.
“Over time, factors such as stormwater mismanagement, leaking services, and environmental cycles contribute to the gradual loss of soil strength.”
Such was the case in Newport, where ground movement was affecting both a residential dwelling and the adjoining rear laneway. Rectify Group was engaged by Hobsons Bay City Council to investigate and remediate the issue, delivering a targeted, non-invasive stabilisation solution that protected both private property and public assets.
Irwin said the Newport site reflected a broader pattern seen across established suburbs.
“At Newport, long-term stormwater issues combined with historical sinkhole infill, using uncompacted crushed rock, led to progressive subsidence and void formation beneath both the property and adjacent laneway,” he said.
“These types of legacy conditions are common across older suburbs and often remain hidden until failure occurs.”
The site had experienced progressive subsidence associated with a previously identified sinkhole beneath the rear yard and laneway corridor.
While the backfill addressed the immediate risk, investigations later confirmed that underlying conditions, combined with ongoing moisture ingress, had resulted in voiding and loosening of surrounding soils beyond the limits of the emergency works.
Over time, poor stormwater control within the laneway allowed water to migrate into the subsurface, washing away fine materials and increasing the potential for further ground collapse.
Additional contributing factors included the presence of nearby mature trees, which influenced soil moisture conditions and exacerbated ground movement through seasonal shrink-swell cycles.
“Laneways are especially vulnerable because they often act as service corridors and drainage pathways, concentrating multiple risk factors,” Irwin said.
“They commonly contain ageing stormwater infrastructure that allows water ingress, as well as service trenches and conduits that create zones of disturbed and loosely compacted soil. Limited maintenance access also means issues can go undetected for extended periods.”
Together, these factors led to a loss of bearing capacity beneath the dwelling’s raft slab and increasing instability within both the rear yard and council laneway.
The impacts were significant. Investigations identified voiding to depths of approximately two metres, with differential settlement across the dwelling of around 128 millimetres, posing an ongoing risk to the structure and adjacent public infrastructure if left untreated.
Investigating without disruption
Given the proximity of the dwelling, the presence of live sewer and stormwater services, and the restricted access conditions within the laneway, a traditional excavation-based remediation approach was neither practical nor desirable.
Rectify Group instead undertook a detailed, low-impact investigation program to understand subsurface conditions without disrupting the site.
“Rectify Group utilises a combination of non-invasive and minimally invasive investigation techniques to accurately assess subsurface conditions while avoiding disruption to the asset or surrounding environment,” Irwin said.
He said the approach combined Dynamic Cone Penetrometer (DCP) testing to assess soil strength, targeted drilling and sampling to identify voids and material variability, subsurface mapping technologies, and internal level surveys to quantify structural movement.
“At Newport, multiple test locations and DCP assessments confirmed voiding and strength loss to depths of approximately two metres, enabling a targeted remediation design without excavation,” Irwin said.
Understanding the full extent of the subsurface conditions, not just the area directly addressed by the initial backfill, was critical in developing a remediation strategy capable of preventing future soil mobilisation and ongoing ground collapse.
With excavation ruled out, Rectify Group designed a resin-based ground improvement solution tailored to the site’s constraints.
Irwin said resin injection was selected for its ability to address complex ground conditions without disturbing surrounding infrastructure.
“Resin injection offered a non-invasive, highly adaptable solution suited to the site constraints, particularly given the presence of active services and variable, non-cohesive fill materials,” he said.
“The resin was able to penetrate and bind the loose crushed rock, fill void pathways, and densify surrounding soils, restoring bearing capacity while maintaining service integrity and minimising disruption.”
The treatment involved a carefully sequenced, multi-depth injection program. Targeted injections at depths of approximately 1.3-1.5 metres improved support adjacent to footing level while safeguarding nearby sewer infrastructure, while deeper injections to around two metres addressed weaker zones and voided soils beneath and around the backfilled area.
Crucially, the resin permeated and bound the crushed rock material, transforming the loose emergency backfill into a consolidated, stable mass. This approach prevented future soil mobilisation, limited the risk of additional collapse, and restored ground integrity without inducing damaging movement to the structure above.
Strong outcomes for Council and community
The remediation works successfully stabilised subsurface conditions beneath both the residential dwelling and the adjoining laneway. Voids were eliminated within the treated zones, bearing capacity was restored, and post-treatment testing confirmed improved ground strength and uniformity.
Irwin said the approach offered clear advantages for councils managing ageing infrastructure in constrained urban environments.
“For councils, this method delivers minimal disruption to residents and traffic, rapid delivery, and cost efficiency by avoiding full reconstruction,” he said.
“It also allows problems to be treated at their source rather than just addressing surface symptoms, reducing risks to adjacent infrastructure and services.”
For Hobsons Bay City Council, the outcome reduced the likelihood of future subsidence impacting public infrastructure and neighbouring assets, delivering a durable, long-term solution without the disruption typically associated with excavation-based repairs.
For the homeowner, the works restored confidence in the performance and safety of the dwelling.
Importantly, the remediation addressed not only the visible symptoms of ground movement, but the broader subsurface conditions contributing to instability.
Irwin said this project highlights the importance of follow-up investigation and consolidation after emergency ground repairs, as untreated voids and surrounding weak soils can continue to undermine infrastructure if not properly addressed.
“Ground instability is rarely a surface issue. It is typically driven by water ingress, poor compaction, and the loss of material through voiding or washout,” he said.
“Undertaking early investigation and avoiding reliance on surface repairs alone can prevent escalation into major failures, reduce long-term maintenance costs, and extend the service life of infrastructure.”
Non-invasive ground improvement methods such as resin injection allow councils to strengthen both emergency backfill and adjacent ground quickly, safely, and cost-effectively, extending asset life while minimising disruption to residents and service networks.
To learn more, visit rectify.com.au
