When something happens that is difficult to explain tunnellers sometimes dismiss the problem by saying that tunnelling is still an “art”. This can be said with a slight air of mystery and even a little pride.

The description of tunnelling as an art is long-standing (books have, quite literally, been written about it). Why? Dictionary definitionsà of “art” include “the conscious use of skill and creative imagination” and “a skill acquired by experience, study or observation”. Science is more about analytical and theoretical explanation of behaviour and engineering is, of course, about the application of such knowledge.

Tunnelling was probably first described as an art because of the tunneller’s need to use skill, experience and even imagination to decide what combination of support would stabilise the ground. Even now many calculations are done with methods derived in part from experience.

We routinely make judgements that contribute to our achievements. Conversely misjudgment has inevitably contributed to some of our failures. Whatever form of tunnelling we practice, we deal in uncertainties. Risks associated with the ground, and the world above us, are always present. The tools we use today to manage these issues include best practice, risk management and the application of experience. Yet these are all forms of engineering judgement that cannot be completely codified.

Thus a tunneller must always be a skilled risk manager: he uses a combination of judgement and book knowledge to achieve (mostly) the right result. So if art implies skill in matters of judgement then in this sense tunnelling is very much an art.

But there is sometimes another implication in the claim that tunnelling is an art. It is sometimes presented as the reason, or even the excuse, for failure to understand and explain. The apparent suggestion may even be that if something can be regarded as an art further rigorous scientific investigation would be futile and unnecessary.

In the nineties the UK industry agonised over design approaches based in judgement and experience (remember NATM and the ultimate sin of “design as you go”?). More recently British major works experience has focussed much more on closed face tunnelling systems. This is an area where technology and world best practice has developed significantly in the past decade. Modern machines continuously stream bewildering amounts of data. The systems are complex and perhaps no one person can be expected to assimilate all the information generated in real time. Is it necessary to work with this data or is it there for later – to prove we built the rings and fend off an auditor perhaps?

&#8220We routinely make judgements that contribute to our achievements. Conversely misjudgment has inevitably contributed to some of our failures. Whatever form of tunnelling we practice, we deal in uncertainties. Risks associated with the ground, and the world above us, are always present.”

Drifter

A diligent engineer will rightly want to use scientific methods to make the most of the all the information available and improve the tunnelling process.

The skill is increasingly in balancing different forms of information to aid the key judgements. So now in the modern TBM tunnels the best results probably come where the engineer’s decisions are heavily guided by continuous systematic analysis of the TBM data.

In many ways our machines are probably still more analogous to Tiger Moths than 747s but nonetheless driving the machine by making judgements largely on “feel” or in response to one or two favoured indicator parameters alone can no longer be the best way.

We need the newer disciplines and the associated competencies but that does not negate the need for traditional skills and experience. It just means the skills are evolving.

So is tunnelling an art or a science? Or was it once an art that has now been swallowed up (particularly in mechanised tunnelling) by the march of science and technology? Or is it simply the skillful application of scientific principles in conjunction with balanced and experience judgement to get the best outcome for a problem (and isn’t that just engineering?). As is so often the case, the truth probably lies somewhere in the middle. But we should not use the terms lightly.

As professional engineers we should strive to make the best possible use of the available science and technology to the benefit of our clients and ultimately our society. But at the same time we must be willing to recognise that there are times when our theoretical knowledge is inadequate. When that happens we still have the same responsibilities and must meet our obligations through the best use of our professional judgment. If that process is best covered by the term art then tunnelling truly remains, in part, an art.

But the fact that tunnelling is an art is a challenge and not an excuse.