Project Spotlights

7 Feb. 2006

Fibermesh® in Underground Railway Tunnel

Concrete Solutions

Project: Sydney, Australia Railway Tunnel
Application type: Shotcrete
Fiber type: Fibermesh® 150
Tunnel engineers: Parsons Brinckerhoff
Contractor:Thiess/Hochtief JV (THJV)

With a total project value of $880 million, Sydney’s new Epping to Chatswood Rail line is not only one of the largest publicly funded public transport projects ever to be undertaken in Australia, it is also one of the country’s biggest-ever underground transport infrastructure developments. Stretching nearly eight miles between the major business center of Chatswood (north of Sydney) to the suburb of Epping, the new underground rail link looks set to revolutionize transport and at the same time set new standards for underground construction – in terms of design, construction methodology and safety.

Fire Safety a Key Concern

This focus on design safety extends beyond the standard operating structural requirements, and also incorporates a number of innovative safety features that are designed to save lives and protect the structural integrity of the project’s underground stations in the event of a fire. One of the key fire safety features is the shotcrete which has been designed to overcome the problems of explosive spalling of the concrete in the event of a fire by the inclusion of high performance polypropylene fiber. Bob Gee, Principal Tunnel Engineer with Parsons Brinckerhoff, the firm responsible for the tunnel design, says, “When it comes to underground construction, explosive spalling of concrete caused by fire can have a devastating impact on structural integrity. When the fire causes a rapid rise in the temperature of the concrete, the moisture in the concrete pores turns to vapor. If it is unable to escape from the concrete mass, the vapor causes an increase in pore pressure, and when this pressure exceeds the concrete’s tensile strength, explosive spalling results.As the concrete deteriorates, it exposes the underlying steel, thus resulting in a rapid loss of strength and load capacity.”

Using Fibermesh® 150

In order to protect the outer layer of shotcrete in the stations huge caverns from explosive spalling in the event of a fire, the design engineers incorporated a shotcrete mix containing Fibermesh® 150 high performance polypropylene fibers manufactured by Propex Concrete Systems and distributed by Tapex Concrete Fibres. Fibermesh 150 fibers not only deliver a range of improvements in the performance and quality of concrete and shotcrete, they have also proven to be extremely successful in preventing explosive spalling in concrete when it is exposed to fire.

Tests Confirm Fibermesh 150 a Wise Choice

The project’s construction contractors,Thiess/Hochtief JV (THJV), in conjunction with the CSIRO’s North Ryde Fire Engineering Section in Sydney, conducted a test of their own into the effectiveness of Fibermesh 150 fibers in preventing explosive spalling. “The results of the Sydney test clearly demonstrated that shotcrete containing synthetic microfibers would be able to provide us with the required 4-hour fire protection and, as such, would be capable of protecting the underlying rock anchor heads in the event of a fire. Following the success of the test, the decision to incorporate Fibermesh 150 polypropylene fibres into the outer shotcrete layer above the springline in the three new stations, as well as throughout the new underground station facilities at Epping station was confirmed,” Gee concluded.

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