The groundbreaking career of rail tunnelling expert Rosa Diez

When most people go for a walk, they look up at the stunning architecture or at the beautiful landscape around them. Not Rosa Diez. Her eyes are fixed firmly on the ground, taking in the layers of sediment in a rock or thinking about the fossils that might be hidden under a city centre paving stone.

It was her fascination with the world beneath our feet, dating back millions of years, that led Rosa to help shape the last three decades of railway tunnelling in the UK and beyond.

“It may sound boring to other people, but geology fascinated me,” recalls Rosa. “I had a really inspiring geology teacher who had a way of making rocks and soil sound so interesting! He encouraged me to look at things differently. People think the ground is stale or stagnant and all the important stuff happens above, but it’s very much alive. Metamorphic processes, plate tectonics, climate change – things are happening under the ground. There’s a hidden life there. And each layer tells a story of how we got here and where we’re going.”

After studying geological sciences at Madrid University, Rosa was unsure of her next move. She was interested in volcanoes, but soon realised that she was too practical and task-orientated for research – and you don’t become a top volcanologist without extensive research. She wanted to apply her knowledge of geological science to something she could actually make a living out of that would also contribute to improving society and the environment. Engineering was the logical choice and early career experience quickly led her into rail engineering.

That decision took Rosa to the UK to study for a Master’s degree in engineering geology at Imperial College London. After graduating, her first job was working on the Heathrow Express rail tunnel collapse which brought her into contact with tunnelling professionals. After working on two more tunnel projects, she knew she’d found her niche.

As well as major international projects in Europe and South America, Rosa went on to contribute to the planning and design of many flagship UK rail tunnel projects, including the £14.8bn Elizabeth Line, which required 42km of new tunnels underneath London. As design manager, Rosa led a 65-strong multidisciplinary team of designers, architects and engineers, pioneering an innovative spray concrete lining technique – a first for the UK rail industry. Advances in excavation technology and concrete quality allowed both the primary and secondary linings to be load bearing, as opposed to the first layer being lower quality, “sacrificial” concrete and the secondary layer ultimately bearing the full load, as previously. This revolutionary technique generated a 25% saving in materials, as well as other benefits, such as health and safety improvements, and is now widely used in rail tunnelling projects around the world.

So what is it about tunnelling, and particularly tunnels for the rail sector, that has kept Rosa engaged and motivated for nearly three decades?

"It brings together all of the things I enjoy and care about,” she says. “I love the problem-solving aspect of it, that’s the mathematician in me, but I’m also interested in the societal benefits of rail. It doesn’t just get people from A to B, it can transform communities, support economic growth and help to tackle climate change."

You never know what you’re going to find underground. I’ve come across everything from huge fossils to burial grounds to unexploded bombs and that definitely keeps it interesting!

While Rosa’s CV is undoubtedly impressive, it is also unusual. Only 15% of the tunnelling workforce in the UK is female and Rosa is one of only a handful of women in senior roles worldwide. She believes this disparity is down to a lack of visibility in the industry, few female role models in STEM subjects in schools and colleges, and the increasing influence of social media which tells girls they should care about more about make-up tutorials than the makeup of the earth.

However, things are slowly improving with nearly a third of A Levels taken by girls now in core STEM subjects. Nonetheless, Rosa is involved in several initiatives to encourage and inspire the next generation of young women to consider careers in tunnel engineering and to keep those women in the industry. As well as collaborating with high schools to offer work placements, Rosa mentors early career female engineers and has also taught at Birmingham University, sharing her tunnelling expertise with Master’s students taking rail engineering modules.

Change is also happening at the traditionally male-dominated UK industry body, the British Tunnelling Society (BTS), which elected its first female Chair in 2020 and now has a Young Members’ Diversity, Inclusion and Women in Tunnelling group. As a member of the Editorial Advisory Board for the Society’s Tunnels & Tunnelling magazine, Rosa has played a significant role in increasing the visibility and influence of female tunnelling professionals, placing women front and centre in the publication. As well as being instrumental in BTS’ first event for International Women’s Day in 2024, she was also responsible for a trailblazing Tunnels & Tunnelling article celebrating the past, present and future of women tunnellers.

“Even as late as the 20th century, the superstition that the presence of a woman in a mine or tunnel was bad luck persisted,” says Rosa. “In 1973, one of the first female tunnelling pioneers, Janet Bonnema, had to take the Colorado Highway Department to court for the right to work underground like her male counterparts. That’s how entrenched the discrimination was and why female tunnellers today are so lucky to have role models like Kate Cooksey, the chair of BTS, who have not only forged great careers but are still active in the industry.

“When I started my career in the UK, there were hardly any female tunnellers and even fewer foreign female tunnellers. I was inspired by one of my fellow students at Imperial, Zuni Iriarte, but she eventually left the industry and I struggled to find other female role models. This is why I feel visibility is so important. Not just to encourage women to join the industry but to motivate colleagues already here to keep going, keep inspiring, keep breaking new ground.”

As we celebrate 200 years of rail, Rosa’s journey from geology student to pioneering rail tunnelling engineer is a testament to the power of looking beneath the surface, both literally and figuratively. Rosa’s expertise has not only helped to shape the railway system in the UK and beyond, she is also changing the cultural landscape. Rosa’s work is challenging stereotypes within the tunnelling and rail industries, showing what’s possible and inspiring a new generation of women to dig deeper into the possibilities of a career underground.