Project Overview
As part of the Maribyrnong River Main Sewer Augmentation project, a deep sewer access shaft was constructed in the inner suburbs of Melbourne. The shaft was built using a large Glass Reinforced Plastic (GRP) vertical liner to provide corrosion resistance and durability in a harsh sewer environment.
Above the GRP shaft, a 34-tonne precast concrete lid was to be installed as part of the chamber’s structural capping. However, due to the delicate nature of the GRP structure, it was critical that no vertical load be transferred from the lid onto the shaft. Engineers developed a solution involving a poured reinforced concrete ring slab that would bear the load of the lid, while sealing and protecting the shaft from external contamination and internal gas leakage.
The Challenge
The project required a long-term sealing solution at the interface between the GRP shaft and the surrounding precast concrete pad and the concrete lid. The design brief called for a:
- Permanent gas-tight seal to prevent the escape of sewer gases.
- 100-year service life to align with project design life requirements.
- Non-load transferring seal over the GRP shaft.
- Durable bearing layer beneath the precast lid to evenly distribute its 34-tonne weight.
- Sealing solution capable of being re-compressed in the event that the lid is removed and replaced in future maintenance works
Solution: Reglin Rubber supplied a composite EPDM rubber seal system in two custom components
Working closely with the engineering team Reglin designed a composite seal which met the key demands of the application. The seal featured 2 different components:
- Outer Ring Seal – EPDM 65 Rubber Sheet (12mm thick)
- Positioned on top of the concrete ring slab.
- Functioned as a load-bearing strip to support the full weight of the precast lid.
- Provided an effective long-term gas and weather seal between the precast lid and concrete ring
Material: Premium EPDM 65 rubber sheet.
Properties: Excellent resistance to ozone, UV, and harsh environmental conditions.
Mechanical performance: Maintains compression set under load for resealing after lid removal.
- Inner Ring Seal – EPDM Sponge Rubber (50mm thick)
- Placed between the GRP shaft and the underside of the precast lid.
- Functioned as a compressible sealing buffer.
- Prevented any vertical load from transferring onto the GRP shaft.
Material: High-compression EPDM sponge rubber.
Properties: Soft, lightweight, high deflection under minimal load while maintaining a gas-tight seal.
Why EPDM?
EPDM rubber was selected by the project’s engineering team due to its proven performance in:
- Chemical resistance to hydrogen sulfide and other corrosive sewer gases.
- Outstanding UV and ozone resistance, critical for long-term outdoor exposure.
- Durability under continuous compression, essential for the design’s service life and resealing capacity.
Outcome
The dual-component EPDM seal system was successfully installed and met all the performance criteria. The combination of solid rubber and sponge materials provided:
- A reliable, long-term gas seal.
- Structural load isolation for the GRP shaft.
- Effective load transfer and leveling for the precast lid.
- Long-lasting weather and chemical protection.
This tailored rubber sealing solution ensured a high-performance interface between modern GRP shaft infrastructure and traditional heavy precast concrete elements in a demanding sewer construction environment.