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Mernda Rail / John Holland (Overpipe)

Project: Mernda Rail Extension project

Location: South Morang and Mernda

Contractor: John Holland, KBR and Metro Trains Melbourne (MTM)

Product: Overpipe

Project Overview

The Mernda Rail Extension project was undertaken by John Holland, KBR, and Metro Trains Melbourne (MTM) on behalf of the Victorian Government and the Level Crossing Removal Authority. The project included eight kilometres of new dual rail line between South Morang Station and Mernda, with five grade separations that guaranteed no level crossings and three new train stations.

Key Challenges          

The issue encountered during construction was the vulnerability of critical buried power and communications infrastructure trackside, which could possibly be damaged by third-party excavation. Construction constraints meant normal depth of cover for this infrastructure could not be achieved. The engineers at John Holland approached Tapex for a potential solution that would avoid the need to have concrete encase or lay concrete slabs over buried conduits (increasing costs and making maintenance access difficult). A further issue created during construction was the requirement to cross and protect existing buried infrastructure.

The Solution

The solution was the use of Overpipe protection plates.

Overpipe was developed for the gas sector, to protect high-pressure gas pipelines from 3rd party damage by excavators or augers. Prefabricated concrete slabs had proven to be cumbersome to handle, expensive to install, of variable quality, and not always effective as a penetration barrier. Overpipe is made from virgin HDPE polymer, is easy to handle, and can be installed manually. Being shipped on pallets, the slabs are cost-effective to transport and are very effective as a penetration barrier and warning device. The 15mm thick Overpipe plates will stop penetration by 36-tonne excavators as well as power pole borers.

SnakePit tracer wire test station is buried just below the cast iron lid (yellow for gas on this sample). The plastic shaft extends up to 600mm below the surface.

Overpipe has replaced the use of concrete slabbing in Europe for pipeline protection and has now been adopted by all major gas utilities in Australia, including APA and Jemena. Once buried, the Overpipe plates will remain effective for centuries. They are also easily removed for maintenance access to buried utilities.

The Outcome

For the Mernda project, the 1500mm x 1800mm size Overpipe plates were used. The plates were customised for Metro trains, and manufactured in white with the embossed legend “WARNING COMMUNICATIONS CABLE BELOW” to comply with the project’s colour and warning requirements.

The project required a total use of 3 kilometres of product.


A cost-effective and practical solution, Overpipe can be made in any colour or with any custom warning message. The plates are 1800mm or 1500mm in length and are designed to overlap 100mm to ensure no penetration is possible where the plates meet. Overpipe plates come in different widths, to suit different trench sizes. They can also be cut down on-site, with a power saw.

Tapex is the exclusive distributor of Overpipe in Australia and New Zealand.