Road over Rail solves the Oaklands Gridlock

MOTORISTS no longer battle boom gates at the Oaklands crossing in Oaklands Park. An underpass now puts the Seaford train line and a new Oaklands Railway Station beneath Diagonal and Morphett Roads.

Trains began servicing the new station on 6 May last and traffic above is moving more smoothly – almost 42,000 vehicles use Morphett Road south of the Oaklands crossing daily. The $174 million project, funded by the federal and SA governments and the City of Marion, is on target for final completion in July this year.

It has involved excavating 70,000 cubic metres of material, constructing a new road bridge, demolishing and rebuilding the station and laying 1.2 kilometres of new track.

A design and construct contract was awarded in January 2018 to the Public Transport Projects Alliance (PTPA), a joint venture of McConnell Dowell, Mott MacDonald and Arup Group.

It has been delivered by the alliance in partnership with the Department of Planning, Transport and Infrastructure (DPTI) and the City of Marion. Site mobilisation commenced in May 2018. The workforce peaked at around 300 during rail connection works from 100 to 120 typically on site each day.

Oaklands station was permanently closed on 13 April 2019 and demolished as works began to realign the tracks to the newly constructed underpass. The Seaford line was also temporarily closed between Brighton and Adelaide to allow the electric catenary for the lines to be shut off for the final works. Substitute buses bridged service gaps as needed between Adelaide and

Brighton while trains continued to operate between Brighton and Seaford railway stations.

The new grade-separated Oaklands station has ramps and stairs down to platform level and a public toilet at street level. A shared pedestrian/cyclist bridge over the rail line provides direct access to the eastern end of the new station platforms.

COMMUNITY ENGAGEMENT

A major planning study by DPTI in 2012 resulted in extensive public engagement from the time of the project’s announcement through the life of the works that followed. Community engagement in 2016 demonstrated a high level of community support and a clear desire to start the project as quickly as possible.

Over 300 people attended two dropin sessions in 2018 to view the project design and provide feedback. Stakeholder management sessions were backed by a 24/7 hotline and project email. Partnerships with local primary schools through STEM (Science, Technology, Engineering and Maths) programs supported study projects at various stages of project construction.

The new crossing and station are expected to catalyse development and renewal in the local area. Travel time via the crossing will be reduced; new pedestrian bridges, pathways and activated crossings will improve

cycling and walking access and safety; and commuters will gain an additional 50 parking spaces at the Oaklands station.

BENEFITS FOR LOCAL INDUSTRY

The SA Industry Participation Policy has provided multiple benefits for SA businesses, suppliers, subcontractors and workers. Major works included:

THE construction of new platforms and station canopies (precast elements fabricated and erected by Bianco, structural steel by Bowhill Engineering and erected by Crane Services, cladding including architectural timber soffit by SA Construct, in-situ concrete elements by Hully).

THE construction of 1.2 kilometres of new track with overhead and underground infrastructure to support the electric trains and signals (drainage and formation by CME Group, steel gantries fabricated and installed by ID Fab, signal and conduit installation by RIC).

THE construction of a bridge over the new alignment (piled foundation with insitu concrete headstocks and wing walls by Torrens Building & Civil, and precast concrete Tee-roff beams by Bianco, and installed by Crane Services); an upgrade of three existing pedestrian crossings to incorporate active-control warning equipment (civil construction by Outside Ideas).

THE relocation of a high-pressure transmission gas line, 900mm water main and SA Power Networks HV and LV services; the construction of new on-street and offstreet car parks (CME Group); demolition of the existing station (Crane Services and Old Red Brick); landscaping the surrounds of the station and access paths (Plot Works); construction of a new amenities building and a control equipment room (Schiavello).

FINDING THE SOLUTION

Construction of the new road bridge in two halves enabled traffic to be diverted from the first half of the bridge allowing the construction of piles, headstocks and finally installation of Tee-roff beams. Traffic was then switched onto the newly constructed half of the bridge so the process could be repeated on the other side.

Excavation of material for the new alignment was carried out either side of the bridge. A temporary retaining wall installed adjacent to the existing station allowed for the alignment and new station to be as close as possible to the existing one without disrupting train services.

As excavation progressed, the walls of the cutting were supported with soil nails and shotcrete. Upon completion of this support, precast architectural panels were installed into the cutting to form the entry ramps and stairs and provide a feature for the new station.

In order to complete the bridge, two major services required relocation as they crossed the middle of the new alignment. A highpressure transmission gas main was diverted from the bridge and sunk beneath the

future rail alignment while a 900mm water main was replaced to fit in under the bridge between the beams.

Once this was done, the remaining bridge beams could be placed and the final offline excavation (beneath the bridge) completed. The cutting station was constructed from precast L-walls for the platform and a structural steel canopy. This was clad with roofing and architectural timber soffit panels installed by SA Construct.

During this time, formation and drainage works were underway by CME Group in preparation for construction of the rail. Gantry columns and beams for the overhead electrical wires for the trains were fabricated and installed by ID Fab. Civil contractor Hully constructed the in-situ concrete elements of the station, including the platform and ramps, while Torrens Building & Civil provided the bridge abutments.

With pedestrian management a key concern, an at-grade pedestrian crossing was constructed across the new rail alignment. The bridge was constructed as a structural steel frame by Bowhill Engineering, and a cast in-situ concrete deck by Torrens Building & Civil, and then lifted into place as a complete unit by Crane Services.

MILESTONES

A key milestone was achieved in September 2018 with the delivery, lifting and installation of nine Tee-roff beams to support the western half of the road bridge. The deck was surfaced and traffic redirected onto the newly installed bridge in early October. Another nine beams were installed on the eastern side. After the eastern deck pour in

mid-December 2018, the project was able to excavate fully under the new road bridge.

Another notable event was the arrival at site in October of a shared pedestrian/cyclist bridge. Constructed off-site by SA family business Bowhill Engineering, the structure is 3.8 metres wide and 17.4 metres long with a 3-metre-wide Aggregate check. Weighing 65 tonnes, it was craned into position, sitting 5.4 metres above the rail line to provide access across the new underpass at the eastern end of the station.

The lowered rail corridor was excavated in levels. Soil nails are drilled two metres deep into the earth walls and set in place with concrete. Steel reinforcement was then attached to the walls and shotcrete sprayed over the nails and steel. These works provide support to the walls and the crews could then proceed with excavating down to the next level, to repeat the process.

Material was segregated into categories of contaminated and clean fill and then transported from site to Adelaide Resource Recovery, Southern Resource and a private development site.

In August 2018, the piling rig was removed from the project site after the team installed 141 piles four weeks ahead of schedule. The project used a continuous flight auger (CFA) piling method. CFA piling involves drilling into the ground, injecting concrete and inserting a steel reinforcing cage.

CHALLENGES

The project posed challenges such as: service relocation of some very high risk/ high value assets; a tight urban site with restricted access in and out of a live rail

corridor; multiple trades working in a restricted area; minimising impacts to residents, pedestrians and commuters.

The services requiring relocation included two APA gas pipelines (a transmission gas main and a high-pressure gas main), two SA Power Networks assets (both 11KV mains), two SA Water assets (a water main and sewer main), and Telstra and NBN communications.

Working next to a live corridor is considered very high risk and the project team managed to keep the old station operational throughout most of the project. Another major risk met by the team was the meticulous planning and coordination of some 300 trades working within the construction zones requiring a high level of communication at all times.

Additionally, the community and stakeholder management team had to embed themselves in the community to minimise the impacts to residents. They provided flyers, door-knock updates and tours, sent text messages, made phone calls and ‘health checks’ on residents, and worked to maintain business access.

INNOVATIONS

The 3D modelling of existing and future structures for the station made it possible to construct and commission the new Oaklands station with minimal impact to rail operations at the existing station. Constructing the road bridge in two halves while maintaining traffic capacity on the road enabled retention of a pre-European remnant river red gum, now a significant feature in the upper plaza level of the station.

The rail alignment was designed to be as shallow as possible to avoid operating beneath the water table – all drainage is above the water table and, as such, reduces the maintenance and operating costs of the dewatering scheme.

The adoption of a precast sump unit for drainage of the lowered railway cutting overcame having to construct a major drainage structure three metres below the water table in what was a confined and congested site.

An Aquifer Storage and Recovery (ASR) reuse scheme allowed the water cart to fill up from the Oaklands Wetlands rather than use potable mains water. This brought the cost per kilolitre down from $3.58 per kilolitre to $2.87 per kilolitre

Written by John SatterleyImages courtesy DPTI..