Consistently pushing the boundaries of trenchless innovation, Edge Underground recently completed a complex microtunnelling project in Sydney that required lateral thinking and customised solutions.
This time, rather than installing sewer or water pipes, Edge Underground installed a canopy tube style structure in order to facilitate the excavation for the future GreenWay tunnel under a rail bridge.
A project that has been in the works for some time, the proposed GreenWay will be an environmental and active travel corridor, linking two of Sydney’s most important waterways. Following the route of the Inner West Light Rail, the GreenWay integrates bike paths, historical sites, public art, community spaces, and natural bushland.
A recent stage of the project required a tunnel to be built under Longport Street – a task that required expertise, adaptability, and innovation.
Edge Underground’s role in the project involved supplying and installing 19 canopy tubes – each 21m long, 508mm OD, 9.5mm thick, mild steel casings – to reinforce the ground and ensure structural integrity for the upcoming commuter tunnel. These canopy tubes were installed and then filled with grout, each forming a solid bar through the ground. Unlike conventional pipeline installations, no infrastructure passes through these pipes; instead, they serve as reinforcement for the tunnel before it is excavated.
This method was chosen to create a structurally stable tunnel beneath Longport Street to allow the bike path to pass through. The existing, longstanding brick built-up embankment and bridge (road over rail) required careful handling to prevent any movement during construction.
Ensuring the integrity of this structure, coupled with a very busy road overhead, added an extra layer of complexity to the project. The authorities have very strict monitoring conditions set for the project as there as several unknowns within the bridge, and settlement was not an option. Additionally, Edge Underground faced several key challenges:
Limited access: Work effectively had to be completed from one end of the project site, with limited access for a reception shaft.
Diverse ground conditions: Drilling through a brick masonry embankment and other unknown fill materials, combined with parts of soft ground, voids and old rail backfill. Large man-made dry wall structures were encountered within the embankment, which also caused issue with the grouting process.
Platform limitations: An adjustable platform was required to manage the installation process efficiently.
No disruption to road infrastructure above or rail infrastructure running alongside the project: Minimising ground movement and maintaining stability throughout construction.
Pioneering microtunnelling approach
As the specialist microtunnelling contractor, Edge Underground deployed an enhanced AXIS machine upgraded with AdaptX technology to execute the works with precision.
The project followed a four-step sequence:
Core drilling through the masonry wall at both ends of each canopy tube.
Microtunnelling the 508mm OD steel casings to exact line and level, forming a structurally sound arch.
Installation and grouting of canopy tubes to secure their positions.
Removal of the microtunnelling platform and conventional excavation of the internal arch to complete the cycleway.
Achieving the project’s goal required both lateral thinking and innovative solutions. Stuart Harrison, Founder of Edge Underground and CEO of OptionX Group, shared some of the key challenges encountered on-site.
“Drilling through up to 1.2m of brick revealed a mix of foreign objects embedded within the masonry – effectively unpredictable fill material – which has the potential to make the process incredibly challenging. On top of that, the surrounding soil conditions were highly variable, shifting from compacted material to lose, soft zones,” he said.
“To maintain accuracy under these conditions, we needed the ability to retract and make real-time adjustments to our casing advancement system and drilling parameters. This ensured we stayed on-line and level while minimising excessive wear on the tooling.”
This custom-engineered casing advancement system was developed in-house by OptionX Group and manufactured at OptionX Bournedrill, reinforcing Edge Underground’s ability to design, refine, and execute custom solutions for challenging projects.
“For a job like this, minimising the number of casings and welds was crucial to maximising structural integrity,” Harrison said.
“We made sure our platform, designed and manufactured by OptionX Bournedrill, could accept the 6m casing.” With the canopy tube arch successfully completed, Edge Underground has stepped away, paving the way for the next phase – the larger tunnelling works – to commence beneath the road.
Delivering efficiency without disruption
Despite the complexities of limited access and varying ground conditions, Edge Underground successfully delivered a safe, precise, and efficient microtunnelling solution with zero impact on road infrastructure above, and no disruption to the major rail service nearby.
The project validated the effectiveness of AdaptX technology and further cemented Edge Underground’s reputation as a leader in solving complex trenchless challenges through engineering excellence and machine adaptability.
Leading innovation
in trenchless technology
Edge Underground’s ability to adapt and innovate sets it apart in the trenchless industry. As part of OptionX Group, it has the expertise, technology, and engineering capability to tackle projects previously considered impossible.
While many contractors turn to OptionX Group businesses for customised solutions, Edge Underground has the advantage of full-time access to this expertise – allowing for seamless innovation and execution on every project.
For more information, visit edgeunderground.com.au
This article was featured in the February edition of Trenchless Australasia.
Subscribe to Trenchless Australasia for the latest project and industry news