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Хочу поделиться ссылкой на интересную статью Learning from difficult rock TBM drive experiences на ресурсе тоннелестроителей : https://www.tunneltalk.com/Discussion-F … drives.php

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Feedback from: Dr Trevor Carter

It was excellent to hear Lok Home give such a frank presentation of ground control difficulties experienced in the three challenging Robbins rock TBM projects he discussed in the BTS meeting. As he stated, this sort of detail is seldom publicised even though many are aware of these types of situation not being uncommon.

The comments he made about prediction inaccuracy of technical bid documents (only 40% accurate in one case) resonate with a theme of increasingly delusional expectations that seem to be prevailing across the industry. The delusion is that fancy geological computer models are necessarily reliable, and worse still that they constitute an adequate substitute for real site investigation data and understanding. The delusion abounds to the extent that all too often wishful thinking geology results in poor TBM designs! Unfortunately, in many cases, when this is found out, it is months after the TBM has been built and when it is now deep under the mountains. Lok’s comments that equipping machines with gear for better forward probing and a need for more mapping in every type of tunnel are spot on, but these techniques are directed only at providing data to help negotiate the now identified problems, but after the fact. By this time the TBM is already built, starting maybe 18 months earlier, based on perhaps erroneous geology data and often based on a far too optimistic or unreliable GBR.

That is where I see the real problem lies – getting better geological and geotechnical understanding into early stages of projects, so that, rather than having to try to retrofit an already built machine to cope with ground conditions that might have been an expected possibility, the necessary capabilities are built into the machine design right from square one.

Fig 1. Searching for the sweet spot between how much needs to be known and site investigation investment(1)
Fig 1. Searching for the sweet spot between how much needs to be known and site investigation investment(1)

Yet again we heard this message from Lok, but this is part of the delusion and applies also to other major parts of a project. This is an old message that seems to be increasingly ignored. My perception is that with increasingly analytical sophistication in geotechnical engineering and enhanced 3D geological modelling and visualization as part of design interpretation, matters concerning understanding actual ground conditions and behaviour (which should be what controls the design and specification for the TBMs according to the ground prediction reports) is getting worse, not better. There is a worrying trend prevalent industry-wide of the increasing use of more and more modelling tools based on less and less real data. This trend towards generating pretty models (with miserable data) is leading to an increasing lack of real understanding. However, the parallel trend to production of GBRs (geotechnical baseline reports) on all projects, while applauded, must be tempered by the fact, as Lok also alluded to, that many are unrealistic, either biased and optimistic at one extreme or too risk averse at the other. Preparation of GBRs that lack a firm factual foundation that provides some bracketing to hard data are merely adding to a delusion of improved risk management, when in fact the reverse is the reality. Risk registers are only part of the answer. Education to counter the delusion that current state-of-practise leads to is the other part of the equation.

As an aid to addressing this worrying trend to delusion through visually impressive modelling, I have upgraded my 1992 risk diagram (Fig 1) to help address three key questions:

How much understanding at any geological complexity level is needed;
How much investigation to achieve that understanding is enough; and
If a given amount of money is spent on geological investigation, can this realistically reduce the risks so well illustrated in Lok’s presentation.
The updated graph (which draws on more recent publications relating to better assessing geological reliability for tunnelling(2,3)), puts into perspective real underground risk versus perceived risk, with data benchmarked to real levels of understanding based on:

How much is a project willing to spend on site investigation;
How much is known about the complexity of the geology; and
The reality of diminishing returns of more extensive site investigation in more complex geology.
Obviously, there is a sweet spot on all projects for deciding how much needs to be known. After that, more expenditure is counterproductive, but below which, too little hard data is dangerous.

On the basis of pay now or pay later, up front expenditure is always better than the reality of downstream claims and remedial works costs. However, nowadays there seems even more reluctance to spend money on upfront site investigation. Hopefully, the graph in Fig 1 can prompt deeper thinking about this. Perhaps at least it can provide some guidelines that project planners can use to start to define how much needs to be spent to adequately de-risk a project, based on where they sit in the scale from simplicity to complexity in their project’s geology. Perhaps with this as a guide we can reduce the number of projects where there is less than 50% accuracy in the geological predictions – such as the three highlighted by Lok.

С уважением,
Игорь