Nick Barton: The Man Who Developed the Best Way to Put Numbers on Rock Quality.

A Conversation With Nick Barton

In this conversation with Nick Barton, we sit down with one of the most influential rock engineers of our time. The man behind the Q-system in 1974 now the most widely used method for tunnel and mine design on the planet reflects on five decades of work across 43 countries. From the non-linear shear strength model that challenged Mohr-Coulomb orthodoxy, to a catastrophic South American diversion tunnel failure that had nothing to do with bad rock and everything to do with bad design, Barton speaks with the candour of someone who has seen unexpected geology humble the best-laid engineering plans more times than he can count. Now co-authoring a new textbook with Professor Stavros Bandis, he remains as focused on what the field gets wrong as on what he believes he may have got right.

System Built to Last 

We started the interview by asking, “You developed the Q-system back in 1974. Over 50 years later, how has it held up, and what would you change if you were designing it today?” 

Nick Barton replied, ‘’The reason it’s held up better than I expected is that it never tried to simplify rock masses into something they aren’t. The six parameters describing block size, joint roughness, alteration, water and stress capture the variability of real geology. And that simple arithmetic, RQD/Jn times Jr/Ja times Jw/SRF, gives you a single powerful number, with a suitably wide range, but the individual histograms keep the underlying statistics alive. That matters too.

What probably cemented its longevity was the link to actual tunnel and rock cavern support design. Engineers could use it on site, the same day for real decisions. If I were starting over today? I might weave in the seismic velocity relationships from the beginning. We now know Vp correlates strongly with Q . So you can estimate rock quality without drilling a single hole. And I’d formalize the depth-dependent permeability work that eventually became QH₂O. But the core thinking? I’d leave it alone. Rock masses are discontinuous, and any classification system that ignores joint character is built on a false premise. It’s now the most widely used method for tunnel and mine stop design in the world, which still surprises me but makes me happy too.”

Breaking the Straight Line 

Times CEO: The Barton-Bandis shear strength criterion is widely used today. What was the key insight that pushed you toward a non-linear model when Mohr-Coulomb was the accepted standard? 

Nick Barton replied, “The insight was actually quite straightforward. You could see it just by looking at rock joint surfaces. They’re often rough. And that roughness doesn’t behave the same way at low normal stress as it does at high normal stress. At low stress, the asperities ride over each other. The joint dilates, apparent friction is high. Increase the stress, and those same asperities start shearing through instead. Dilation disappears. You’re left with a high residual friction.

A straight Mohr-Coulomb line can’t capture that transition; it’s just not in the geometry of a straight line. The JRC-JCS model gives us measurable field parameters for joint roughness coefficient and joint compressive strength. These describe what is actually happening physically.

And it’s not academic. Dam abutments, deep tunnels, steep rock slopes, jointed petroleum reservoirs  –  in every one of those situations, the stress regime changes dramatically across the structure or during time. Getting the shear strength wrong at the wrong stress level has real consequences.”

The TBM Trap 

Times CEO: Your QTBM method predicts TBM performance in jointed and faulted rock. What are the most common mistakes engineers make when making TBM prognoses about likely performance? 

Nick Barton replied, “The biggest one, by far, is fixation on penetration rate in meters per hour of actual boring while completely ignoring the deceleration that sets in when you hit difficult ground. Early in a drive, crews improve with their new machines and learning rates climb. That’s the part everyone talks about. But in wet jointed or faulted zones, that trend can reverse sharply and fast. QTBM was built specifically to capture that deceleration phase, because that’s where schedules collapse and budgets go off the rails. The second mistake is borrowing machine performance data from one geological setting and applying it to something fundamentally different. Cutter thrust, rock strength, prevailing stress, and the degree of jointedness and water inflow all interact. Change the geology and the new numbers mean something different. The geology and hydro-geology always have the final word

The Failure that was remembered 

Times CEO: You’ve worked across 43 countries and hundreds of projects. Is there a particular failure that taught you more than any success? 

Nick Barton replied, “There’s one that still bothers me, even though I wasn’t involved in the design. The Q-system was used correctly, in isolation on a South American hydroelectric project. The designer applied standard Q-based support: as for a dry tunnel, light single-shell shotcrete, rock bolts. Perfectly reasonable for an ordinary tunnel. But this was a high-velocity water diversion tunnel with water flow speeds of 35 to 40 kilometres per hour, in other words over 10 metres per second in a big tunnel.  There was no erosion protection. The floor wasn’t concreted. And to make it worse, there was a sharp bend right after the intake from a rising reservoir.

What followed was a 100-metre diameter erosion cone to the surface. Then two more. Emergency flow was finally through the power house. A delay of four or five years and a massive claim by the owner. The contractor did nothing wrong. It was the design. What that taught me is that no empirical system protects you from not asking the right questions first. The Q-system tells you about rock support. It doesn’t tell you what happens when you add ten times higher velocity of water to the equation. That’s the engineer’s job.”

Engineering for Eternity

Times CEO: Nuclear waste disposal requires rock mass integrity over geological timescales. How do you approach making predictions for timeframes that dwarf any monitoring record? 

Nick Barton replied, “You have to be honest about what you can and cannot claim. No monitoring programme validates a 100,000-year prediction. That’s just not possible. What you can do is demonstrate that you understand the governing physical processes, and that your site geometry places the repository outside the reach of anything likely to breach containment. In my work on nuclear waste projects in the US, UK, and Sweden, the best focus was on deep crystalline rock with negligible groundwater circulation and minimal seismic risk.

But the thing that isn’t yet taken seriously is a phenomenon I have called thermal over-closure. Rougher rock joints behave differently under thermal loading and cooling than smoother intersecting joint sets. The parameter changes are significant. In both nuclear waste storage and geothermal energy applications, these effects matter and they’re still not being considered. More lectures needed!

The Textbook That Was Missing 

Lastly, we asked, “You’re co-authoring a new rock engineering textbook with Professor Stavros Bandis. What gaps are you most determined to fill?” 

“The fundamental disconnect between how rock mechanics is taught and what rock masses actually are. Most textbooks default to continuum mechanics because the mathematics is tractable. I understand why but rock masses aren’t continuous. They’re assemblages of blocks, defined by joints and faults and foliations, and it’s those discontinuities that govern their behaviour. Everything I’ve worked on Q, Barton-Bandis, QSLOPE, QTBM, QH₂O is built on that premise.

We want students to be able to stand in front of a rock face, look at it, understand its structural geology, and develop physical intuition before they reach for unrealistic continuum programs. One of the popular codes has a subjectively estimated variable appearing 78 times! Users do not seem to have noticed! Stavros brings exceptional depth on joint behaviour normal loading, shear loading, scale effects. That complements the broader field characterisation and project applications that I contribute. In most existing textbooks, joint properties and rock mass properties might get condensed into a single chapter. We’re giving them the space they deserve. The goal is a book that’s genuinely useful on sites not something you shelve after your final exam.” Nick Barton concluded

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