Mtenacity is defined as adhering to a concept with vigor, and tenacity can be described as a virtue under certain circumstances. However, it depends upon what you are being tenacious about. For instance, no one doubts the tenacious adherence that Austrians have for their beloved tunneling method commonly referred to as the "New" Austrian Tunnel Method (NATM.) No matter what anyone says or how any project turns out the Austrians just keep beating the NATM drum, and to their credit, they have procured an enormous number of tunneling assignments for themselves throughout the world. If things go well, they declare victory and publicise the hell out of the project. If things do not go well, they blame Mother Nature, the contractor, the construction manager, bad luck, etc. and declare that if only more Austrians had been involved with the project then "so and so" never would have happened. Hence, the Austrians must be duly recognised for their tenacity.
However, just what is it about the NATM that demands such a singular adherence to a particular method for making a hole in the ground? Prior to the 1950’s the majority of rock tunnels were excavated by drilling and blasting and supported by rather crude methods involving mostly wood but also steel ribs, bricks, or dressing stone. Soil tunnels were advanced using shields under sometimes difficult circumstances that required compressed air in order to control the face.
As pointed out in my paper on the history of tunneling (Tunneling: A Historical Perspective, August 2014 Tunnel Business Magazine) it is truly amazing to realise what tunneling professionals accomplished prior to the 1950’s with the tools available to them at that time.
During the 1950’s, however, several significant tunneling advancements began to materialse that revolutionised tunneling for civil engineering projects. Foremost among those advances was the use of Tunnel Boring Machines.
As a result of numerous technological advances it became possible to make circular holes in rock using with roller cutters into which a shield could be advanced. Hence, both the method for excavating the ground and the methods for supporting the ground were streamlined to a considerable degree.
As a result of TBM development, the tunneling industry began to refer to the drilled and blasted method for advancing a tunnel as "conventional" in order to differentiate those tunnels from TBM tunnels.
It was also during the 1950’s that the civil engineering profession began to take notice of rock bolts and shotcrete. Prior to the 1950’s, rock bolts and shotcrete had been used primarily for various mining applications but civil engineers also recognised the significant advantages of rock bolts. For instance:
1. Rock bolts can be used to create a safe opening. With blocky rock, rock bolts are used on a pattern basis to make certain that loose blocks of rock do not fall down and create a dangerous environment in the tunnel.
2. Rock bolts also allow the rock mass to be reinforced so that it can support itself. Reinforced rock is just like reinforced concrete. Curved rock arches reinforced with rock bolts greatly facilitate rock arching and cause the ground to support itself to a large degree.
3. Finally, rock bolts prevent large nonuniform loads from impacting the tunnel lining. In the old days, it was possible for large blocks of rock to shear through the lining and come crashing down into the tunnel. Rock bolts, when used properly, prevent this from happening.
Similarly for shotcrete. Shotcrete is cast-in place concrete that is placed pneumatically and the pneumatic placement of concrete produces many advantages that are particularly applicable to tunneling projects. For instance, pneumatically placed concrete can be placed in thin layers that serve as temporary support.
With time, this layer can be increased in thickness as the ground loads increase and/or as the opening is made larger. Indeed, the thickness of pneumatically placed concrete can be increased to the point where it constitutes a final lining just like concrete placed behind a form. Probably the biggest advantage of pneumatically place concrete is that there is no doubt that the concrete is in firm contact with the rock mass and is therefore available to form a stable arch that will work together with the rock mass in order to support very heavy ground loads.
There is nothing either magical and/or mysterious about using rock bolts and shotcrete to support the ground and literally thousands of both civil engineering and mining openings around the world have been stabilised in this manner without any input or assistance from Austrians. Historically, rock bolts and shotcerete were a natural and innovative advancement for the conventional method of supporting rock just like TBMs were a highly innovative method for excavating rock. For instance, rock bolts are often used to support a rock mass behind a TBM which is sometimes supplemented with shotcrete, but no one, except maybe a few Austrians, claim that this is an extension of the NATM.
In conclusion, the author of this article believes that there are several aspects of the Austrian’s tenacious adherence to their tunneling method that many tunnelling professionals find infuriating. For instance:
1. NATM is not a "method" of tunnelling any more than any other method associated with the conventional excavation and support of rock masses.
2. Rock bolts and shotcrete have been understood and used by tunneling and mining professionals throughout the world for many decades; most of whom have never set foot in Austria.
3. Austrian designers have been able to convince impressionable tunnel owners to specify Austrians for work on a project to the detriment of other fully capable and knowledgeable tunnel designers.
4. The Austrians would like the world to believe that they "invented" some mysterious method for supporting the ground back in the 1950’s that only Austrians understand and that only Austrians can put into service. There are two problems with this claim: Number 1, lots of different designers from lots of different countries participated in the historical development of using rock bolts and shotcrete to support the ground, and Number 2, those concepts are now so well established that they are readily available to every well-educated and well-experienced tunnel designer.
Final thoughts and moving forwards
So, there you have it. While the author of this article is willing to recognise the Austrian’s tenacious devotion to self-promotion he is equally perturbed by their claim of having invented a "method" of tunneling and of having some magical power over the behavior of rock bolts and shotcrete. The author also firmly believes that the Austrian engineers might find it exhilarating once in a while to actually specify a TBM tunnel, or to use an open face shield in the proper ground condition.
The expression "When all you have is a hammer, every problem looks like a nail" certainly applies to the NATM.
In the final analysis, it seems that it would be highly beneficial, both for the tunnelling industry as a whole, and also for the Austrians, if they simply stopped blabbing about how smart they are and just stated designing safe, stable, and cost effective underground openings like tunnel designers from the 200 or so other countries around the world.
