Forrestfield-Airport Link – Environmental Outcomes

Now known as the Airport Line, the METRONET Forrestfield-Airport Link included two 8km tunnels, three new stations and a total 16km of rail infrastructure.

From 2016, the Public Transport Authority and Webuild-NRW JV worked collaboratively to achieve a minimum Infrastructure Sustainability (IS) Excellent Design Rating and Leading As-Built Rating. The project was the first rail project in Western Australia to achieve an IS rating.

The commitment to a sustainable project started at the very beginning – with the decision to move the 8km rail line underground.

Impacts to the environment (flora and fauna) were reduced by the decision for tunnelling in general, rather than building surface infrastructure. This was especially important as the infrastructure was built in densely populated urban areas, and near and on the Perth Airport estate. Perth Airport is the major gateway to WA due to the State’s large distance from other capital cities, not just for travellers, but also for freight, and impacts to air traffic would have had a major flow-on effect on the economy.

Environmental and heritage considerations were a key priority and detailed planning occurred to ensure areas of significant environmental value were identified, managed and reported on early. Environmental Management Plans with appropriate measures and controls were implemented and continuously monitored during construction.

Minimising water consumption

Perth has a drying climate and water is a scarce resource. Minimising the need for water and implementing water recycling initiatives were a key focus in the design, construction and operation of the project.

Water-saving initiatives included recycling water during the tunnelling process, with a water treatment plant at the High Wycombe construction site.

Recycling water during the tunnelling process achieved the biggest reduction in water usage. A filter press and centrifuge were used to separate water from excavated material - water was then recirculated to the tunnel boring machines (TBMs).
During operations, smart monitoring is installed to detect water leaks and reduce the water consumption.

Tunnel segment production

A purpose-built pre-cast concrete segment facility was constructed in close proximity of the tunnelling, enabling streamlined manufacturing and reduction in haulage. Over two years, 9098 rings (54,588 segments) were made at the factory.

The concrete solution used for the manufacture of the segments was based on a hybrid system using steel fibre-reinforced concrete and light steel reinforcement rebar cages. Polypropylene fibres were incorporated within the concrete mix to comply with the fire resistance requirements.

In consultation with the supplier, a low-carbon concrete blend containing 65% Supplementary Cementing Materials (SCM) was successfully developed

In addition to meeting environmental requirements, strict quality and durability specifications needed to be met with more than 40 concrete trials conducted in the product’s development, winning the final mix the 2019 Concrete Institute of Australia (WA) Award for Excellence in the Technology and Innovation Category.

Solar panels

Forrestfield-Airport Link has the largest solar panel system installed by a WA State Government department/corporation, with the plan to see this become the norm within the Public Transport Authority (PTA).

Water saving initiatives

The expected amount of water used during construction was reduced by 30 per cent (2740 megalitres) through the recycling of water used by the TBMs and other plant. Water pipes were connected from the water treatment facility in High Wycombe, to the TBMs as they tunnelled 8km to Bayswater.

An innovative water reclamation, treatment and recycling system was implemented during tunnel construction. The system consisted of several interconnected components on all the major flows associated with the system, and modelling was undertaken to determine the volume of water that was recycled and reused.

Tunnel segments
Use of traditional concrete (~10% SCM) would have required 550kg/m3 of cement. For the Forrestfield-Airport Link, the final concrete blend for the tunnel segments composed of only 230kg/m3 of cement – this resulted in a total saving of 21,848 tonnes of CO2 emissions.

The purpose-built facility enabled the project to have greater control over the production quality and quantity, resulting in less waste. The facility was purposely located in close proximity to the tunnelling activities, keeping heavy haulage distances at a minimum.

Post-product development, the project successfully obtained Greentag certification, an EPD and an environmental innovation award from Cement Concrete and Aggregates Australia (CCAA), the peak body for heavy construction materials industry in Australia.

The high-SCM concrete blend was able to meet the projects 120-year design life requirements. This translates to lower maintenance requirements during the asset’s life.

Key sustainability initiatives were also achieved in the manufacturing of tunnel segments:
• 46 per cent of the cementitious material was recycled by-products composed of silica fume and blast furnace Slag. These two constituents, along with General Portland (GP) Cement, created a triple blend cement, significantly reducing the amount of higher energy intensity cementitious material required.
• To achieve the required 60MPa compressive strength, only 230kg/m3 of GP cement was used compared to 550kg/m3 used as the benchmark for similar strength concrete.
• The steel fibres incorporated into segments came from 20 percent recycled material. Of the 3200t of steel fibres used for the segments, 640t came from recycled origins.
• The concrete waste material from the wet and dry concrete bins was converted into either 19mm concrete road-base or 20mm drainage rock.
• An onsite Waste Water Treatment Plant, treating stormwater and used potable water from the batch plant. The system was designed to treat 62.5kL of stormwater with a catchment area of 665sqm and 10kL in the upstream wedge-pits. There were two tanks to treat the contaminated water to appropriate levels – the water was then reused for batch plant washdowns, and segment mould cleaning.

The efficiencies and sustainability initiatives have been shared through industry papers, conferences, social media channels, including the Transport Minister’s social media, as well as industry magazines.

Further knowledge sharing events were also held between Webuild-NRW and individuals working in the sustainability space on other PTA and Main Roads infrastructure projects.

Solar panels

The 278kW solar array installed at High Wycombe reduces the station’s consumption of grid electricity and is associated with a saving of 35,904 tCO2 over the lifetime of the project. This will reduce the energy consumption of the asset by about 4.33%.

The installation of the solar panels and saving have been shared as a benchmark to use in future decision making on all major rail projects. It has also been shared at industry conferences, and via social media.
The solar energy has a lower carbon footprint than that produced by fossil fuels for the Perth grid. The main environmental benefits include:
• Reduction in greenhouse gases and other air pollution traditionally produced for electrical production
• Reduction in the use of finite resources (coal and water) in preference of the renewable source from the sun.

PTA has shared the lessons learnt and successes from the installation as a benchmark to use in future decision making on all major rail projects.

The successful approach to solar power has been repeated at the first new train station built since the Airport Line opening, Lakelands Station. A large array of solar panels was installed on the station’s bus interchange canopies, as was the case at High Wycombe Station.

The sustainability initiatives provided whole-of-state benefits, translated down to the individual with tax payer money saved on maintenance (120-year life span of infrastructure). The reduction of emissions and use of resources contributes to a better and more sustainable environment for generations to come.

The development of the high SCM concrete blend for the tunnel segments, and subsequent product promotion and market recognition was a step toward changing business-as-usual in the construction industry. This case is a clear example that sustainable practices do not have to come at the expense of durability, quality or profit.

Throughout the planning, design and construction stages of the Forrestfield-Airport Link project, our sustainability vision was for an innovative and sustainable project, providing a solution for enhancing the connectivity, liveability and prosperity of Perth and its eastern suburbs including the airport.
A lasting legacy has been achieved through the infrastructure’s a 120-year design life, as well as the upskilling of employees and businesses, economic support to WA and Australian businesses and local stories and history captured in the Public Art.
UN SDG contributions include:

Goal 8 – Decent work and economic growth
During design and construction, the project supported economic growth in delivering large-scale public transport infrastructure and the longest tunnel in WA. We supported a diverse workforce and implemented opportunities to up-skill people of all ages within the tunnelling and construction industry.

Goal 9: Industry, Innovation, and Infrastructure
As well as providing new public transport opportunities to the eastern suburbs and Perth Airport, the project built resilient infrastructure (120-year design life), delivered innovative initiatives, and continued to support the local economy and workforces during the COVID pandemic.

Goal 11: Sustainable Cities and Communities
The social and economic benefits of the Airport Line cannot be understated, particularly in boosting employment, residential and economic growth, especially around the stations.
In addition, during construction Webuild-NRW boosted the local economy by awarding more than 90% of the total $1.1billion of contracts to Australian companies; 65% of these were from Western Australia.
Further, the Airport Line has increased public transport options for the 60,000-strong and notoriously underserviced catchment area of the eastern suburbs and foothills, significantly reduced travel times from the eastern suburbs to Perth’s CBD by public transport, reduced car dependency for both nearby residents and those travelling to the airport.
It has also created additional capacity on Transperth’s existing Midland and Fremantle lines to meet growing passenger needs, relieved pressure on Perth roads, supported domestic and international tourism with improved access between the city and Perth Airport.

The project has also made the way for new opportunities for development in the area, with support of the local government. Opportunities being reviewed for development near the station includes an aquatic centre and civic place for local residents.

Goal 12: Responsible consumption and production
The water saving initiatives during construction, and solar panel use during operations, both support the goal of responsible consumption and production to achieve the sustainable management and efficient use of natural resources.

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