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Member Success Story: Bekaert's Involvement in the M4-M5 Link Tunnels Project, Sydney

Bekaert, a global leader in steel wire transformation and coating technologies, aspires to be the leading partner in shaping a safer, smarter, and sustainable future. Renowned for its expertise in material science, Bekaert provides innovative steel wire solutions for the construction industry, ensuring structures meet the highest standards in speed, cost-effectiveness, safety, and durability. 

Benoit De Rivaz, the Global Business Development Technical Manager for Bekaert Underground Solutions, is at the helm of this success. With a decade dedicated to Dramix in tunneling applications and a rich background in international tunneling projects, Benoit shares more on Bekaert's involvement in the M4-M5 Link Tunnels Project.


Introducing the M4-M5 Link Tunnels Project

Bekaert played a crucial role in the success of the M4-M5 Link Tunnels project in Sydney, Australia. The 7.5km-long tunnels connect the new M4 Tunnels with the M8 Tunnels, forming the 33km-long WestConnex Motorway. 

The project involved innovative solutions to address challenges faced by past applications.

The Challenge

The M4-M5 Link Tunnels project in Sydney faced substantial challenges in Permanent Sprayed Concrete Lining (PSCL) applications, requiring a departure from adhesion reliance for long-term performance. 

All thin linings must perform under fire exposures of four hours ISO and two hours HC both during fire incident and post-fire with a residual load capacity. These new requirements drove a minimum thickness of sprayed concrete to be 130mm or greater, even in relatively competent rock.

Pioneering these changes, the project team innovatively redesigned the mix, prioritizing high structural performance, notably in flexural capacity. A key transformation included introducing groundbreaking high-strength steel (1850MPa) double end-hook fibers, a first in Australian sprayed concrete.

Challenges included validating design improvements through large-scale testing in a field confirmation phase. High-performance shotcrete facilitated specialized design methods, crucial for proving the capacity of thin linings.

Validation tests followed EN 14651, confirming the performance class mini per MC 2010. The final mix achieved targeted structural performance with a strength of 40 MPa and residual flexural strength values (fr1 > 3.5 MPa and fr4 > 3MPa), overcoming industry challenges.

Numerical demonstrations showcased compressive membrane action significantly enhancing flexural performance, setting a precedent for future advancements in sprayed concrete technology.



How Dramix® 4D65/35BG Steel Fibres Were Used

Recognizing past challenges with concrete reinforcement, the M4-M5 Link Tunnels project took a decisive turn at its onset, opting for a transformative solution – Dramix 4D65/35BG steel fibres. This high-performance end-hooked steel fiber addressed historical non-conformance issues and design checks, offering a promising alternative to traditional methods.

Introducing Dramix 4D65/35BG brought a compelling value proposition, delivering equivalent technical performance to conventional reinforcement but significantly reducing steel usage by up to 60%. This strategic reduction enhanced the project's efficiency and markedly reduced its carbon footprint, aligning with sustainability objectives for underground construction.

Dramix SFRC's outstanding performance, particularly in hardening post-crack behavior validated through a three-point bending test, ensured effective crack control during Serviceability Limit State (SLS) conditions and enhanced structural ductility under Ultimate Limit State (ULS) conditions. 
Designed for permanent sprayed concrete applications, Dramix 4D65/35BG demonstrated optimal crack control capabilities thanks to its innovative glue technology that addressed fiber balling during mixing and ensured a homogeneous distribution of fibers throughout the concrete mix. 

With features such as high tensile strength exceeding 1800MPA and a fiber network of 16,000 lm/m3 at a minimal 30 kg/m³, Dramix 4D65/35BG emerged as a pioneering solution, setting new benchmarks for concrete reinforcement in the project.

Benefits Achieved

The use of Dramix 4D65/35BG resulted in notable performance benefits. The tunnel linings saw a 15% reduction in sprayed concrete thickness and a 10% reduction in reinforced steel fibers. It also demonstrated cost savings of $11,000,000. 

Benoit emphasized: 

"To maximize the use of such high-performance shotcrete, the design adopted for the tunnel lining also included a concept not previously used in designing thin tunnel linings with rock bolts: compressive membrane action."

The project also substantially reduced sprayed concrete usage and reinforced steel fibers, resulting in environmental and cost-saving benefits. Benoit highlighted the success: 

"After more than 250,000 m3 of steel-fibre reinforced shotcrete sprayed in the project, the project confirmed a successful and consistently conforming application of this higher performance shotcrete with an overall quantity reduction in shotcrete of between 15% to 20%.

The tunnel linings, incorporating Bekaert's steel fibers, were designed for a 100-year lifespan with a focus on sustainability. 

The decision to use SFRC aimed to reduce shotcrete quantities, achieve cost savings, and promote environmental sustainability. Bekaert continues to explore recyclability, contributing to a microplastic and pollution-free solution.

Bekaert's involvement contributed significantly to the project's recognition with the Excellence in Economic Outcomes Award by the Australian Infrastructure Sustainability Council. The value proposition of using high-performance shotcrete fibers at lower dose rates played a crucial role in the project's success.





ITA WORKING GROUP 12: LOOKING AT THE PAST TO BUILD A MORE SUSTAINABLE FUTURE FOR SPRAYED CONCRETE

Sprayed concrete experts from the International Tunneling Association (ITA) Working Group 12, several of them members of EFNARC, got together early this month during the World Tunneling Congress 2022 (WTC) in Copenhagen to discuss the past, present and future of the sector. 

EFNARC president, Max Eckstein, and representatives from Bekaert, Sika, Normet and Master Builders Solutions attended in person the Working Group session, which put together some of the professionals with most expertise in the industry and several of them joined the group by video call.

The group’s Animateur and Senior Specialist Engineer at the Norwegian Geotechnical Institute, Karl Gunnar, highlighted three main topics above the rest: their most recent published report on permanent sprayed concrete linings, their current research on how permanent sprayed concrete degrades over the years and the role sprayed concrete will play in constructing more sustainable tunnels, slopes and in other applications.

The report Permanent Sprayed Concrete Lining, produced by the working group and ITAtech in 2020, touches on aspects like design, sustainability, durability or safety. It also emphasizes the need for objective certification schemes and simulator training, such as the EFNARC Nozzleman Certificate that uses a virtual reality simulator to train and assess applicants.

“We need the training process, a structured way of training and certifying people in order to get the application process right”, said Gunnar in an interview after the meeting.

As one of the most numerous and diverse ITA working groups, with representatives from companies, academia, the public sector and industry associations, amongst others, one of the challenges discussed by Working Group 12 is how to improve communication and collaboration between the members of the group and external stakeholders.


The thinner the better

Sustainability and reducing the carbon footprint was the key theme of the congress and, as with the other working groups, it will influence the actions and decisions of the Working Group 12 in the following years.

However, the group is first looking at the past, in particular, how the sprayed concrete looks after a number of years in operation, how it degrades, with the intention of using their research to improve the design and make it more sustainable in the future.

“The potential of sprayed concrete is to construct even slimmer linings, with less carbon footprint and much less concrete, so the working group 12 has a great responsibility in order to get that process documented and motivated in the industry”, says Gunnar.

In line with this, the group listened to two presentations during their meeting.


International expertise

The first presentation was held by David Oliveira, Technical Director at Jacobs, about permanent sprayed concrete linings at Westconnex M4-M5 Link Tunnels Project in Sidney, and the second one by Cristobal Menquehual, PhD Candidate at the Norwegian University of Science and Technology, about in-situ conditions and lifetime assessments of sprayed concrete linings in Norway.

The conclusions of the Australian presentation confirmed that high-performance end-hooked steel fibres achieve high-level performance ground support with only minor and expected outliers. 

On the other hand, Menquehual’s presentation, that is also his PhD thesis, outlined that shotcrete joints are in most of the cores the weakest part of the lining and determined that shotcrete porosity values near the rock should be below 21% in order to be resilient.

The group plans to meet before the  WTC 2023, which will be held in May 2022 in Athens, Greece, and is working on a new report about in-service conditions of sprayed concrete linings.

The World Tunneling Congress 2022 was organized earlier this month by ITA-AITES and the Danish Tunneling Society (DFTU) and held in the bright Bella Center Copenhagen with more than 160 innovation-sharing lectures and speakers from over 30 countries. 

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