When Helen Nattrass arrived at her first tunnelling site in Newcastle in 1986 and asked where the tunnel boring machine was, the project manager pointed to the canteen.
"They're in there having their breakfast," he said. Inside was the gang of tunnellers, many of them Donegal Tunnel Tigers. It was the beginning of a working relationship that would take Helen and the Tigers all the way to the Channel Tunnel, one of the greatest engineering projects ever attempted.
Helen from York, in England, had graduated from Imperial College London ten years earlier with a degree in Engineering Geology. She became a Fellow of both the Institution of Civil Engineers and the Geological Society of London. But despite her qualifications, she knew that underground, success depended on the men at the tunnel face.
"Loads of them, " she said immediately when asked if she'd worked with
Donegal Tunnel Tigers, recalling names of Donegal men like Frank Cardiff, ‘Bull’ Reilly, Dickie Brennan, Joe Gallagher, John Ryan, Tom Mulleary, Tom Gorman.
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From Ranafast to the Rock Face: A life carved in darkness, dust and survivalTunnelling is a close-knit trade, and Helen often worked with the same crews repeatedly on different projects across Britain and Europe. When asked what it was like to work with Donegal men, she said it was great. "They were extremely friendly, tremendous workers and, above all, great craic. They were serious about safety and their work but loved having fun on the job."
Trust Underground: Where Safety and Bonuses Depended on Each Other
From 1987 to 1990, Helen worked as a Senior Geotechnical Engineer, Tunnel Construction and eventually managed a whole team of geologists on the Channel Tunnel. Her role was critical. Deep exploratory boreholes had been drilled at one-kilometre intervals between Shakespeare Cliff in Dover and Calais in France to predict ground conditions. But boreholes can't tell the whole story. Helen's job was to constantly check what the tunnel boring actually hit against what the surveys predicted, and to react fast when things didn't match.
A major part of her role was building trust with the Tigers. Neither could do their job without the other. If unexpected ground conditions appeared, Helen had to quickly assess the danger and help design solutions. But if the answer caused delays, it hit the Tigers' bonuses. From the start, she ensured the men understood her responsibilities and why certain decisions had to be made. She held them in the highest regard and knew that many were far more intelligent than their manual work might suggest.
Reading the Ground Before the Main Attack
The Channel Tunnel consists of three tunnels: two for trains and a smaller service tunnel for emergencies. A smart decision was made at the beginning of the project to drive the service tunnel ahead of the main ones. This let Helen and her team of engineering geologists check ground conditions in advance of the running tunnels within a smaller space.
For the first three kilometres from Dover, the ground was more fissured than the boreholes predicted. These cracks arose from ancient geological stresses locked in the strata below the tunnel horizon. As those stresses were released over the millions of years to the present day, tiny earthquakes caused fissuring that was difficult to identify in boreholes. These mini-earthquakes can still be felt occasionally in Kent.
The smaller service tunnel could handle such fissures at a pinch, but they would prove extremely problematic for the larger train tunnels, having a big impact on progress. Helen and her fellow engineering geologist friends collaborated with senior managers and designers, deciding to pump grout from the sides of the service tunnel into the rock, which would be above the roof of the big tunnels following on. This strengthened and sealed the ground before the Tigers excavated the main tunnels. This took place about a kilometre ahead of the main tunnelling operations so that progress on the main service tunnel, and the tigers’ bonuses, was not impacted too much.
False Alarms and the Fear of the Sea
The small service tunnel was also the location of consistent horizontal probe drilling ahead of the face to make sure they were not tunnelling into a big seawater problem. At times, other probe holes were drilled, for example, to check over the roof of the crossover cavern.
On one occasion, while an exploration borehole was being drilled at an upward angle at the side of the crossover, the cooling water from the drill-string suddenly filtered out of cracks some distance away in the crossover cavern workings. In an instant, the mood changed.
The Tigers believed the unthinkable had happened, that the seal to the English Channel had failed and that the sea was breaking in. For a brief moment, instinct took over and there was a nervous retreat back down towards the exit.
Helen, however, remained absolutely certain that no breach had occurred. She knew the water was simply tracking through fissures in the rock and not the Channel itself. Once the initial panic subsided, and out of respect for the men at the face, she explained precisely what had happened and why there was no danger. Calm returned, work resumed, and confidence was restored.
Later, she admitted that the thought briefly crossed her mind of jokingly throwing a fish onto the tunnel floor at the coalface, just to underline the moment. On reflection, she decided the joke was better left unmade.
The Underground Cathedrals
The toughest job was building the massive underground crossover that allows trains to switch tunnels in emergencies. This space is so large it’s been called an underground cathedral.
It was too big for tunnel boring machines and had to be dug in small stages, supported with steel lattice-girders and sprayed with shotcrete concrete as work progressed. Nothing of this scale had been attempted anywhere in the world under the sea. Despite all the planning, success relied on constant monitoring and close cooperation between Helen’s team and the Tigers. Through close collaborative teamwork between the engineering geologists and the Tigers the works were successfully completed without a glitch.
Where Geology Met Graft
The Channel Tunnel's success depended on the working relationship between the engineering geologists and the Tunnel Tigers. Surveys and predictions weren't enough.
Safety and progress relied on constant comparison between what was expected and what was actually found. Helen and her crew provided the technical assessment and solutions. The Tigers provided real-time intelligence from the tunnel face and executed complex work under demanding conditions.
Trust was central. Decisions that affected safety, pay, and productivity were explained openly, not just imposed. When unexpected conditions appeared, responses were quick and collaborative.
In 1988, one year into production, both Helen and the Tigers had their work recognised when Prime Minister Margaret Thatcher visited the site. Meeting the Prime Minister underground was a moment of pride for everyone involved, a recognition that what they were achieving beneath the Channel was of national and international importance.
This relationship delivered one of the most complex civil engineering projects ever undertaken. The Channel Tunnel stands as a monument not just to engineering, but to the skill and courage of the men and women like Helen who dug it, including the Donegal Tigers who left home to work beneath the sea.
Eamonn Coyle is a Chartered Engineer and Chartered Environmentalist
