Hi dear colleagues,
There are four empirical methods (AFTES, Bieniawski, Barton and Terzaghi) that can be used for the design and sizing of tunnel lining. However, these methods don't have well-defined assumptions or rigorous scientific justification, because they come from the experience of one or more people, rather than from scientific research. My question is: what is the most used empirical method for the tunnel lining design and sizing?
Thank you in advanace
Dear Hamid Gadouri,
Special care must be exercised that tunnel should be designed by three approachs together: emirical (e.g. rock mass classification system), analytical (e.g. numerical modeling) and observational. Doing either of these alone is a major error.
Rock mass classifications are indeed empirical, which seem to be not very rigorous scientific, but these systems represent a wealth of accumulated practical experience from case histories and provide the reality of current engineering judgment.
Both RMR and Q are in the same category of assessing rock mass quality for tunnelling purposes and providing input for engineering design and construction.
Thank you so much Dr. Tingchang Yin for the answer. Also, I appreciate your valuable comment given above in the first paragraph regarding the main three approachs that must be considered together for tunnel lining design and sizing.
I believe the use of empiricism is an accepted and widely used component of the'scientific method'. While the questioner is right that one or very few are involved at the start - such as selecting enough but not too many parameters - the essence of the method is to select, test, adjust (re case records and the need to adjust parameter ratings to get better fit, even to add a missing parameter). In the case of the Q-system this was 6 solid months of work at the start (but not the several years some have assumed). However the collection of numerous tunnelling case records (by Grimstad) was for sure some years in total. We are indebted to him.
Thank you very much Pr. Nick Ryland Barton for this valuable addition. Personally, I agree with you regarding the great work done by Grimstad in collecting of numerous tunnelling case records. Indeed, he deserves our great respect for what he has done for civil engineering science.
Just to clarify further, lest the questioner and others think that only empirical methods (in our case Q) are of interest to the developers of Q. There are two factors to consider. In the case of an important 'semi-stationary' project like a big cavern, there is both time and the reasonable need to check empirical design - for instance modelling a small number of possible rock classes with the associated jointing. One can recall the insight given by UDEC-BB studies of the ultra-big Gjøvik cavern, testing different levels of horizontal stress. Then there are special EDZ studies for nuclear waste disposal, which may include access ways, and disposal caverns (ILW, LLW) or HLW tunnels. Hundreds of numerical models - to complement Q-system application. Less frequently also 3DEC models, but with the present disadvantage of only MC joint description.
The second point is that tunnels (as opposed to caverns) advance much too fast for 'continuous' numerical modelling, so here the daily even several-times daily advances of say 4 to 6m need a quantitative description beyond 'adjectives', and demand appropriate selection of 'the day's' tunnel (permanent) support class. Critics of empirical methods can criticise to their heart's desire - but they need to suggest a practical alternative - e.g. in a country with more than 5,000 km of tunnels, and an institution or design company that has had responsibility (in the past) for more than 1,000 km of hydropower and road tunnels, with particular participation of former colleagues Løset and Grimstad. Q or its equivalent was urgently needed, and arrived, unplanned, as an answer to a pressing need.
Make sure that with your last comment the vision has become very clear.
I thank you again Dr. Nick Ryland Barton for your time and valuable information's that we can't find it in libraries or on the Internet, but we find it with the experts like you and who are worked near these mega-projects. I think that it would be better to collect all these information's to be consulted at the time of need.
An initial design based on an empirical approach (Q & RMR), followed by a realistic numerical model, results of which are constantly verified and validated using field observations is the best way to design any underground structure either tunnel or caverns. The main constraint in execution of these stages is the time in hand and project completion schedule on your head. as an engineer, you need to adjust the design steps/procedure appropriately to also suit construction progress. This is all about engineering the design.
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