Suburban Rail Loop
Soft-Eye GFRP Rebar for Diaphragm Walls, Melbourne
Stations: Alex Fraser, Monash, Clayton & SSY
Project Overview
The Suburban Rail Loop (SRL) East is one of Victoria’s largest infrastructure projects, delivering a new 26 km underground orbital rail line connecting Cheltenham to Box Hill. The project includes six new underground stations and will transform travel across Melbourne’s south-east, with trains expected to begin operating in 2035.
As part of the station box construction, diaphragm walls (D-walls) are being installed at key sites including Alex Fraser, Monash, Clayton and SSY. These reinforced concrete walls form the permanent perimeter of the deep station excavations and must allow safe, efficient Tunnel Boring Machine (TBM) breakthrough.
The Challenge: Enabling Safe TBM Breakthrough Through Diaphragm Walls In underground rail construction, Tunnel Boring Machines must pass through the diaphragm walls of station boxes and shafts. Traditional steel reinforcement in these zones creates major problems:
- Steel is extremely difficult for TBM cutters to penetrate and risks severe damage to the machine
- Manual removal of steel is slow, costly and high-risk for workers
- Any delay in breakthrough impacts the overall tunnelling programme
A reliable “soft-eye” solution was required — a dedicated cuttable zone within the D-wall that maintains full structural capacity during excavation yet can be cleanly cut by the TBM when it arrives.
The Solution: High-Performance GFRP Rebar for Soft-Eye Applications We supplied BlackBar™ GFRP rebar (glass fibre reinforced polymer / FRP composite rebar) specifically for the soft-eye zones in the diaphragm walls at Alex Fraser, Monash, Clayton and SSY stations.
GFRP rebar is the proven material for soft-eye applications because it is:
- Fully cuttable by TBM disc cutters without damaging the machine
- High-tensile strength, providing the required structural performance of the D-wall until breakthrough
- Corrosion-resistant and non-conductive
- Lightweight, improving cage fabrication and installation safety
- Compliant with Australian Standard AS 5204
By replacing steel with GFRP rebar only in the designated soft-eye panels, the D-walls retain full strength and stability throughout construction while allowing rapid, safe TBM entry and exit.
Project Outcomes and Benefits The use of GFRP rebar soft-eyes delivers clear advantages for the Suburban Rail Loop:
- Faster and safer TBM breakthroughs with no need for manual steel removal
- Reduced risk of damage to expensive Tunnel Boring Machines
- Improved programme certainty for station box and tunnelling works
- Long-term durability of the permanent D-wall structure
- Alignment with modern best practice for major metro and rail projects worldwide
This solution supports the efficient delivery of critical underground stations that will serve Melbourne for generations.
Why Choose GFRP Rebar for Soft-Eye and Diaphragm Wall Applications? GFRP rebar is the industry-standard solution for soft-eye zones in diaphragm walls, secant piles and TBM launch/retrieval shafts. It combines structural performance with cuttability, making it ideal for complex underground rail, metro and tunnelling projects across Australia.
Contact us today to discuss GFRP rebar solutions for soft-eye, D-wall and tunnelling applications on your next major infrastructure project.
