Common Ground

Geology is in essence an observational science. There is a limit to the amount of geological experimentation that can be carried out when one is dealing with Planet Earth. So geology is advanced through observation. Take for instance the geologist’s role in mapping out a potential ore body. Often weeks, if not months, are spent mapping outcrop and building up a model of the local geology. A firm grasp of geological principles is required to do this – what are the rock types which outcrop in the study area? What is the 3D orientation of lithostratigraphic units or the tectonic structures preserved therein? How does this all hang together in interpreting the formation of an orebody? These are but some of the questions that a geologist asks in the field. During the fieldwork the geological map is added to, showing the spatial distribution of the various rock types as they are mapped.

With time, the map becomes more complete. However, where there is no outcrop to be found, a certain amount of extrapolation is required, often with a little ‘geological’ licence thrown in to complete the geological model. Back in the office, samples are examined under the microscope to determine their mineralogy and assist in assessing their geological history. But it all fundamentally boils down to careful observation in the field, and then bringing to bear knowledge and experience to interpret the geological history of the area.

In summary then, a slow, methodical, interpretative approach is required to solve a geological problem, often assisted by a contemplative walk between each outcrop and field sketches to test various hypothesis concerning the spatial distribution of the rock units. Perhaps a drilling programme is then put together to prove the mineral target and with any luck the potential ore body might become a mine.

Compare this then to the civil engineer whose training is decidedly orientated towards the numerical. Arriving at a number is imperative, and understandably so when calculating bending moments, loadings, shear strengths, tensile strengths and factors of safety. An understanding of the physical properties of a range of materials is fundamental to any design; the most obvious examples being steel and concrete. Coefficients of expansion, effects of corrosion, the performance of concrete, fluid dynamics, surveying, soil mechanics and foundation design are some of the subjects which any good engineer should have a working knowledge. Some of these concepts can be exceptionally abstract and require a high degree of numerical skill. That said, they are all quantifiable, and the strengths of almost all construction materials are either well documented or can be directly measured in the laboratory. Which of course doesn’t leave much scope for extrapolation or interpolation.

Little wonder then that the civil engineers want to draw straight lines between the various soil or rock horizons which may have been recorded in a series of boreholes. Little wonder that they are uneasy with a dotted line populated with question marks on a geotechnical map. Little wonder that what a geologist may be comfortable with, an engineer isn’t. The different approaches may lead exasperated hair pulling in the various camps, and it is at this juncture that we need to find the common ground. To some, this common ground might in fact be no-man’s-land or terra incognita. Engineering geologists, bless them, make their living in this, at times, barren place. However to have a foot in both camps they need to have a firm grasp of geology, augmented by an understanding of soil and rock mechanics, hydrogeology and foundation design.

Civil engineers who venture into geotechnical engineering bring to the table a formidable array of skills which are eminently applicable to the subject. Their numerical and problem solving skills and rigorous training are assets to the profession. Geologists who venture into geotechnical engineering bring to the table a formidable array of skills which are eminently applicable to the subject. Their observational and data collection skills, ability to see the problems in a 3 dimensional way and an understanding of the origins and hence engineering behaviour of a particular soil type are assets to the profession.

Clearly there is common ground here, and an understanding of the different approach taken in training graduate engineers or geologists throws some light on how they approach any geotechnical problem. Each camp does have a valuable contribution to make. The engineers are always responsible for the design, but need to draw as much as possible on the skills of the geologist to arrive at the best geotechnical model for the site. On the other hand, engineering geologists need to be cognisant of the burden of responsibility that rests on the shoulders of the engineer, and in this light enhance their numerical and engineering skills which will enable them to become valuable members of any team.

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