GeoZone Geotechnical Services My Geotechnical Fantasy

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					GeoZone Geotechnical Services My Geotechnical Fantasy
Gerald Allan Davie M.Sc. (Leeds) Pr.Sci.Nat

Back in the 1990’s I returned to South Africa flush with new found knowledge and enthusiasm. The reason of course being that I had just completed my Masters degree at that old and venerated institution of learning – Leeds University. The course was recognised as one of the big three for this kind of training, the other two being Imperial College and Durham. We had been immersed in soil mechanics, rock mechanics, shear boxes, triaxial tests, strain gauges, transducers, data loggers, hydrogeology and so the list went on. Graphs of every parameter under the sun had been plotted, equations and bearing capacities had loomed large in our thinking, and although an immense amount of work, we had all enjoyed ourselves thoroughly. Armed with all this knowledge I came home to apply it, only to find that it was in many ways irrelevant, due to a number of reasons. I found that I was digging test pits at 200 to 300 m spacings, that no one was doing any kind of real laboratory testing, shear strengths were being guessed at, SPT N values, so much at the heart of bearing capacity calculations, were unavailable. The bearing capacity equation became a trifling, discarded on the rubbish heap labelled ‘no budget’. What were the characteristics of a soil or rock for which we were providing recommendations? No one was very sure. A lack of understanding Perhaps there was another factor playing itself out – a lack of understanding by management of the subtleties of soil mechanics and an unspoken acceptance that this work was beyond the scope of the engineering geological community. Maybe this was due to many ‘engineering’ geologists having received no formal training in the subject, with associated lack of numerical skills and a lack of a profound understanding of the testing and interpretation thereof. For whatever reason, the outcomes have not been entirely satisfactory. There are too many cases of broad brush, fudged, reports – written to cover a lack of knowledge due to inadequate site investigations, lack of laboratory testing and to some extent a lack of understanding of the geotechnical complexities which often prevail on a site. There is also a willingness by the engineering geological community to defer to the engineers, which is understandable seeing that the engineers are ultimately responsible for their designs. However if the engineering geologists are to ensure the integrity of their profession, they need to be more forthright in their view of what needs to be done in terms of characterising a site.

Good Information It all boils down to getting good information. I need to dig enough test pits, take enough samples and conduct enough laboratory tests to build my geotechnical model. One test pit per 10 hectares is not enough. I know some of you will say that the guidelines to which I am referring cover various scenarios – namely, investigations for planning, investigations for urban development and specialized geotechnical investigations. But all too often a site only gets one geotechnical investigation, and that is the planning one – and as a result there is not enough information to thoroughly assess the prevailing geotechnical conditions. And bear in mind that the guidelines themselves state that they are “the minimum requirements.” Why do we have to go with minimum? What happened to ‘best?’ And then of course they are only ‘Guidelines’. Don’t get me wrong – I am grateful that there are such guidelines, and it in some ways they make our lives easier. But it means that everyone in the engineering geological community, particularly when the insidious 3 quote system is being applied, will price a job based on the minimum requirements so as to win the work. I don’t think I need to spell it out, but you get what you pay for. So to all the engineers out there, it is probably not be in your best interests to insist on the 3 quote system as you may well be getting a substandard product. My geotechnical fantasy And in this light I am going to tell you my geotechnical fantasy and so I beg your indulgence. Wouldn’t it be absolutely fantastic to have a well written geotechnical report based on a decent number of test pits, dynamic probing and laboratory tests? If a multi-storey structure is to be built, well, I would like to drill boreholes and carry out Standard Penetration Tests. If I am looking at the stability of a slope I need to know the shear strength parameters of the soils which make up that slope and so undrained and drained triaxial tests are necessary. It might of course be a cutting in rock – again I need to characterise the shear strength of the discontinuities. In summary then, all of us, whether engineering geologists, civil engineers or planners, need to beware of adopting a laid back attitude to the substrate on which all our civils projects are founded. Dedicated geotechnical professionals with an eye both for the geological and civil implications of any project are to be valued. Geotechnics is in many ways a dark art, and only by throwing the cold light of enquiry into those dark recesses can we hope to be of benefit not only to our clients, but to ourselves. We here in South Africa are so good at many different things, often working under difficult circumstances, and in spite of this we are at times world beaters. Perhaps we could beat the world on the geotechnical front too, or at least aspire to a far higher standard to which we currently hold ourselves. If you enjoyed this newsletter please pass it on to colleagues, friends, juniors or the boss, and if you would like to read more, visit, and have a look at what else is on offer on the website too while you are about it. Kind regards Gerald Allan Davie

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