Forbes Overbridge

Reinforced Earth® Arch & Wingwalls
TechSpan® & TerraPlus®

Location:
Forbes, NSW, Australia
Owner:
Rail Infrastructure Corporation
Consultants:
Cardno BMK (NSW) Pty Ltd
Contractor:
Rail Infrastructure Group
Construction:
January 2002

With many of Australia’s inter-urban rail links being a popular method of transport for passengers and goods alike, the Rail Infrastructure Corporation (RIC) undertook an upgrade of a number of existing wooden bridge structures in NSW. One such structure was located just outside the township of Forbes, southwest of Sydney.

The Forbes overbridge was an aging wooden structure, used extensively for goods transport. Due to the rail lines heavy trafficking, it was imperative that the upgrade, involving dismantling of the existing bridge and the erection of the new structure, take place within a single weekend to minimise disruption to the rail traffic.

The Reinforced Earth Company (RECO) was contracted to design, supply and supervise the erection of the Forbes Rail Overbridge in January 2002.

A 10 lineal metre precast tunnel incorporating approximately 70m² of TerraPlus® concrete retaining wing walls was designed to accommodate the current rail specification 300LA (AS 5100). Due to a low clearance to the rail loading, a 1m thick layer of 4% cement stabilised material was installed above the arch to guarantee uniform bearing.

The stringent time restraints required all the construction materials to be onsite prior to erection commencement. The arch/wall footings were poured and cured by rail hand-over at 6am Saturday morning and dismantling of the existing structure then began.

The rail lines were cut and the existing structure removed, seeing the erection of the tunnel beginning at 12pm Saturday afternoon. Completed by 4pm, the assembly of the wingwalls could begin.

The base row of panels had been located and propped accordingly, allowing for the commencement of backfilling. The panels and backfill were placed continuously throughout the night with the final compaction layer completed at 7am Monday morning.

The contractor then worked tirelessly to ensure the structure was completed by 12 noon Monday. The ballast was reset with the rail lines being re-attached and completed on time. The first train passed over the new structure at 6pm Monday evening.

On this particular project it was necessary to briefly close the railway line, however TechSpan®

arches can also be easily constructed over existing roadways and railways without the need to stop or divert the traffic.

Similarly, a great benefit of building a Reinforced Earth retaining wall along a road or railway is that it does not need scaffolding or any structural footing in front of the facing. As a result, the wall can be built from the rear without interruption to traffic.

All components were precision manufactured to ensure RECO’s TechSpan® tunnel and TerraPlus® walls worked seamlessly together. This high level of detail was critical to the projects success.

 

  • Complete replacement of the Railway Bridge with 10m of TechSpan® arch and 70m² TerraPlus® wingwalls in 60 hours.
  • Stringent time constraints requiring precision planning and execution of installation.
  • The ability of RECO to provide a total precast solution ensured the successful delivery of this project on time.

Project Specifications

System
TechSpan® & TerraPlus®
Structure
Tunnel & Wingwalls
Area
6.5m Span & 70m²
Height
3.975m arch & 3.78m walls
Length
10m tunnel & 35m walls
Design Load
100kPa(DL) 130kPa(DL+LL)
Design Life
100 years
Finish
Plain

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