Toowoomba Bypass – Constructing the Viaduct

Isaac Kirsch

Department of Transport and Main Roads

Abstract: The $1.6 billion Toowoomba Bypass, formerly referred to as the Toowoomba Second Range Crossing

(TSRC), is a 41 kilometre heavy vehicle route jointly funded by the Australian and Queensland

Governments under a Public Private Partnership with Nexus Infrastructure. The route is designed to

increase freight efficiency and improve driver safety and community amenity by removing a

significant number of heavy vehicles from Toowoomba’s CBD.

The completed Bypass connects the Warrego Highway at Helidon Spa in the east to the Gore

Highway at Athol in the west via Charlton. The TSRC creates a safer, faster and more efficient route

for connecting freight to major ports and markets.

Figure 1: Location of Toowoomba Second Range Crossing and the Viaduct.

The project features:

• four lanes (two each way) from Warrego Highway east interchange at Helidon Spa, to

Warrego Highway west interchange at Charlton

• two lanes (one each way) from Warrego Highway west at Charlton to Gore Highway at Athol

• grade-separated interchanges at Warrego Highway east, Warrego Highway west,

Toowoomba-Cecil Plains Road and Gore Highway

• grade-separated connections to Mort Street and Boundary Street in Toowoomba City

• a 30 metre deep cutting at the top of the Toowoomba Range, with the continuity of the New

England Highway by two arch bridges over the cutting and

• an 817m long viaduct connecting the Lockyer Valley and Mount Kynoch.

Of particular note, is the viaduct, which is a new engineering and construction process for the

Darling Downs and Lockyer Valley regions.

Construction of the viaduct commenced in September 2016 and was completed in December 2018.

It is comprised of:

• 26,000 cubic metres of concrete

• 5,000 tonnes of reinforcement

• 120 piles between 6m and 20m deep

• 21 piers (22 spans) ranging from 12m to 51m in height

• 242 pre-stressed concrete super-T girders (11 per span)

• super-T girders ranging in length from 30.366m to 37.804m and a mass of 71.3t to 88.5t

This paper explores the details behind the design and construction of the viaduct.

Keywords: Toowoomba Bypass, Toowoomba Second Range Crossing, viaduct, piers,

construction, methodology

The viaduct travels east to west, with Abutment A being in the east and Abutment B on the west.

Construction of the viaduct commenced in September 2016, with piling beginning at Abutment B,

and its construction was completed in December 2018.

Figure 2: Aerial photograph of the Viaduct. Abutment A (east) on the left, and Abutment B (west) on the right of the image.

The 817m structure comprises 22 spans, hence the term ‘viaduct’, ranging in length from 33m to

38m. The maximum grade motorists will experience travelling up or down the range is 6.5%, which

is a significant improvement on the current infrastructure which reaches a grade of 10%. The lower

gradient will assist heavy vehicles to maintain a higher travelling speed which will consequently

reduce travel time. The predicted time saving for heavy commercial vehicles across the whole

project is expected to be approximately 40 minutes, which includes bypassing 18 sets of traffic lights

through the heart of Toowoomba.

Figure 3: Long section of Abutment B (west)

There were several constraints associated with the construction of the western end of the viaduct,

including a high-pressure gas main and a rail line owned by Queensland Rail. To address these

challenges, vibration limits were implemented during construction in the vicinity of the high-

pressure gas main, which were closely monitored. In addition, a temporary bridge was constructed

over the gas main to allow access to the construction site and ensure that the proximity of the

construction traffic did not directly increase the forces applied to the gas main and potentially

causing damage. The rail line required Pier 21 to be constructed as a solid reinforced concrete blade

wall to withstand the potential impact of trains de-railing. This differs from the other viaduct piers

which are hollow. Furthermore, the construction program (particularly the launching of girders

overhead) was required to coincide with approved rail closure dates.

The foundations of the viaduct consist of piles with a pile cap. There are six 1500mm diameter piles

per footing except for the four shortest piers which have just four piles per footing. The piles range

from 6m to 20m long, based on the geological conditions of the site and mass of the structure the

footings were designed to support. Each pile cap contains approximately 70 tonnes of steel and 250

cubic metres of concrete.

The piers, which stand between 12m and 51m tall, are supported by piles. The piers are hollow with

300mm thick walls and constructed in approximately 4.5m lifts/sections, with a total of 126 lifts

required across the entire structure.

Figure 4: Pier construction.

Lifting formwork, steel and equipment around the site was undertaken by two tower cranes that

maintained a 60m swing radius to aid in the efficient movement of materials. These cranes were

located at four different locations as the works progressed. Additional mobile cranes were brought

on site, when required, dependent on the tasks required each day.

Constructed on top of the piers are headstocks. These had their own challenges given the

constricted work area, including limitations applied by the scaffolding design and restricted access to

the platforms. In addition, due to the isolated location, workplace health and safety risk mitigation

required regular rescue drill exercises to be conducted using stretchers to ensure the safety of

workers on-site should an emergency occur.

The girders, ranging in length from 30m to 38m with a mass between 71 tonnes and 89 tonnes, span

between the headstocks. The girders are 1.8m high and are designed with voids in them to help

reduce their mass. This however created some difficulties during construction. To maintain the void

design in the girders, fibre cement sheets were placed over each void prior to laying the steel for the

bridge deck. Occasionally the sheets would break, either during transportation/handling or from

reinforcing steel dropped on them as the bridge deck was being formed. This created two potential

risks, including:

1) workers falling into the void, sustaining serious injury, and/ or

2) concrete could burst through the sheet when being poured and filling the void.

To prevent possible injury to workers, stainless-steel mesh was placed over the entire bridge deck

which was designed to prevent penetration of the fibre cement sheets.

To manage the risk of concrete breaking through the sheet, the project team ensured good work

practice and care was taken when pouring the deck.

Figure 5: Girders being placed by the truss girder launching gantry. Note: Between the reinforcing bars (loops) are the voids which have

the cement fibre sheets already placed over them.

Transporting the excess dimensioned girders from the casting yards in Brisbane, up the 10% grade of

the existing range crossing, through Toowoomba City proved a challenging exercise in itself. The 242

girders required to construct the viaduct were only a portion of the total 500 super T's required for

construction of the entire Bypass project, all of which were transported via the existing range

crossing. The up lanes of the existing range crossing were temporarily closed to traffic from 12am to

4am to allow for the safe transportation of these oversize units.

Over 100 nights of temporary closures were required, with a maximum of four girders transported in

a single night. The temporary closures meant significant planning was required to implement

detours (for both light vehicles and other heavy vehicles), manage emergency services access, and

contingency planning for possible breakdowns partway up the range crossing, or for delays in

delivery which required girders to be laid down mid-journey until the following shift. The girders

were then stored at Abutment B until they were lifted into place by the truss girder launching

gantry.

Figure 6: Girders stored at Abutment B until transported to the viaduct by the launching gantry.

The use of a launching gantry solved several erection difficulties such as access to the bridge for

girder deliveries, crane positioning, and the shear height of the piers. During construction the

launching gantry proved to be an efficient means to manoeuvre and position girders and was an

engineering highlight of the overall process.

The launching gantry consisted of the main truss which operated as runways for the winch platforms

and enabled the self-launching operations. Erection supports bore the load of the gantry and the

girders, as well as providing anchor points for the gantry and allowing transverse movement during

girder installation. The master and slave winches, when coupled, performed the lifting and lowering

of the girders and when anchored to the erection support, allowed for the self-launching.

The process of girder installation:

• the gantry moved all the way forward on the bridge deck into its receiving position

• the girder was transported from Abutment B down to the gantry by two straddle carriers

• the gantry moved back above the girder, and the winches raised the girder into the body of

the gantry

• from here the girder was moved forward by the winches to a position in between the

forward two erection supports

• the gantry then moved forward until the fore lip was positioned on the first auxiliary

support. This was then repeated until the girder was in place above the required span

• the girder was then moved in a transverse direction (if required) and lowered into its final

position by the winches.

Figure 7: Aerial photograph of the launching gantry during girder installation.

This process was repeated for each girder, with the erection supports moving one pier further east

each time a span was completed.

While this process was efficient, particularly with the heights involved, it was a slow process. The

time taken to install each girder varied between two to five hours, with the edge girders taking

significantly longer to install due to the constraints in movement imposed by the launching gantry.

Between three and five girders could be installed each day. Safety risks were minimised by reducing

human and machine interaction using remote control operation of the straddle carriers and

launching gantry, which proved to be another benefit of the girder installation process.

Once each span of girders had been completed, finishing works were carried out including the

concrete deck pours, installation of edge barriers, construction of slip form median barrier,

installation of anti-throw screens, bituminous waterproofing and asphalting of the bridge deck, and

finally linemarking.

Figure 8: Completed viaduct looking west

The Toowoomba Bypass toll road, including the eastern section between Helidon Spa and Cranley

and the viaduct was opened to traffic on 8 September 2019.

Commencing from the 9 September 2019, there is a three-month toll-free period in place to allow

motorists the opportunity to use the road and experience the benefits.

Acknowledgements Department of Transport and Main Roads

Nexus Infrastructure

References Department of Transport and Main Roads, Toowoomba Second Range Crossing, 2019, accessed

January 2019, https://www.tmr.qld.gov.au/Projects/Name/T/Toowoomba-Second-Range-Crossing

Nexus Infrastructure, Toowoomba Second Range Crossing, 2019, accessed January 2019,

www.nexustsrc.com.au

This has been a condensed summary of the design and construction of the viaduct which aimed to

highlight some of the more critical and interesting elements of the viaduct. Please note that this

paper does not attempt to address the design, construction or management practices, nor risk

allocation and contract positions of the project and for the sake of brevity, focuses only on a high-

level review of key components and issues.

A PowerPoint presentation was delivered to accompany this paper, presented on 24 October 2019.

Project information can be found at the TMR website - https://www.tmr.qld.gov.au/TSRC