Geologists versus Engineers, it’s an age-old joking point in the underground construction industry. A geologist will tell you an engineer goes about his calculations by thinking of a number, then doubling it – just to be on the safe side. He’ll also say that the resulting number is irrelevant, as the engineer will only break whatever it is he’s doing anyway. An engineer will presume the geologist is drinking herbal tea in the office whilst sharpening his impressive set of colouring pencils, or sowing another leather patch on the elbow of his trusty field jumper.
But in tunnelling, and I mean more specifically through hard rock where fault zones are common, the roles can be quite mutually exclusive, and attention to, and experience with, both can be invaluable. This month, Professor Richard Goodman gives us a unique insight into the life and works of geomechanics ‘guru’ Professor Gunter Riedmüller, who passed away in 2003.
Riedmüller was a fierce supporter of obtaining extensive geological information at the earliest possible stage of a project, saying: “The engineering geologist should act as a coordintor and, in cooperation with the construction engineer, should draw conclusions from the great number of geological results obtained for use in structural design.”
He was also wary of the engineer’s seeming dependence on ‘generalised correlations of rock behaviour with rock mass ratings’, and felt that they should only be applied at early design phases. He was also, and more specifically, a leader in research into the presence of smectites in fault zones, which can lead to deformation.
With this in mind it would have been interesting to hear his verdict on the recent roof fall in the Hanekleiv tunnel, in Norway, where smectite in a fracture zone has been labelled as the ‘very likely’ trigger. It appears that, although a concrete lining had been used at other locations, at the point of collapse only rockbolts and shotcrete had been used. The geomechanics involved in the collapse took some 10 years to occur, but it does appear that the presence of smectite, coupled with inadequate support lead to the fall.
Would this have still happened if such early stage geological mapping and support assessment had been carried out, as was the norm for Riedmüller, is impossible to say. But it could have gone a long way to prevent Norway now being in the un-enviable position of having to remedially check many more of its rock tunnels for fear of the same circumstances in other areas leading to further collapses.
Tris Thomas
