NZ Geomechanics News


Geotechnical engineering is the first and most important aspect of any infrastructure or urban development project. The engineering geologist usually hits the ground first and is charged with developing a geotechnical ground model that makes sense to the engineer who will be designing the structure (road, dam, tunnel or building). Over the course of my career many new trends have developed and many have become standard practice in analysis, design and construction, and/or in associated site investigations.  Not all of them have been good for our profession. In particular, I live in fear of software that purports to build a believable geological model, and I’m even more fearful of those who believe in and unquestioningly use such models. 

GIS and UAV’s are marvellous things, LiDAR and InSAR offer opportunities we didn’t have not very long ago, and mobile phones that know lots of tricks are great toys. But, as Don U Deere (the RQD man) once said in a Review Meeting: “Geology is done through the boots”. I have never forgotten that pearl of wisdom – it was the truest truism of my career!  And I want every young engineering geologist and geotechnical engineer to remember it – and more importantly, believe it!

The ground will always surprise us.  Most of us can tell stories of finding ground conditions within metres of a drillhole or test pit that were completely different from those predicted from the data. I have personal experience of a well-drilled slope that turned out not to be a landslide despite apparently convincing drillhole data (although to be fair, less convincing geomorphology).  And that ‘landslide’ model was not generated by a computer, it was hand-drawn from careful, detailed consideration of a lot of point data. Maybe the computer could have done better (probably not back in 1990), I know it would have thought a lot faster, but given the complexity of that particular site that was exposed by the excavations I choose to remain sceptical.  “Geology is done through the boots” does not refer only to field inspection of ALL sites for which you have responsibility, it also includes thinking about every piece of data, how it fits (or does not) the conceptual model, what the implications are for the model and for the way in which the ground might behave. 

Once you have a story, get it reviewed by someone else! I can tell horror stories about sites where the interpretations were not reviewed or challenged – ultimately these just make lawyers happy. You do not want to go there.

And talking of surprises – read the article on erionite! Like me, you may have never heard of it, but for some of us it might be VERY important to know more.

NZ Geomechanics News
Don Macfarlane
NZ Geomechanics News>Issue 98 - December 2019

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