Geotechnical Instrumentation

“Every geotechnical design is to some extent hypothetical and every construction job involving earth or rock runs the risk of encountering surprises.  These circumstances are the inevitable result of working with materials created by nature… by processes seldom resulting in uniform conditions.  The inability of exploratory procedures to detect in advance all the possibly significant properties and conditions of natural materials requires the designer to make assumptions that may be at variance with reality and the constructor to choose equipment and construction procedures without full knowledge of what might be encountered. Field observations, including quantitative measurements obtained by field instrumentation, provide the means by which the geotechnical engineering can design a project to be safe and efficient, and the constructor can execute the work with safety and economy. “

Ralph B Peck, 1988

For those not in the know, Ralph Peck is “the godfather of soil mechanics”, and in his day was directly responsible for a succession of celebrated tunnelling and earth dam projects that pushed the boundaries of what was believed to be possible.  In a way, Peck has summed things up totally and it could be argued that there is nothing more to be added on why geotechnical engineering in general, and instrumentation in particular, is so important.  But then again, some elaboration may be called for as to why we should instrument our civil engineering and mining projects.

Firstly, there are enormous benefits to be had during the design of a project.  Instrumentation may be used to assist in assessing the in situ geotechnical conditions during the design phase.   A simple example is the installation of piezometers to monitor groundwater levels and hydraulic head.  More complex examples include the assessment of in situ stress and deformability conditions in the design of tunnel linings or large, underground excavations.  By understanding the geotechnical conditions, a more focussed and optimal design can be arrived at.

Furthermore as Peck indicated earlier, designs have inherent uncertainties and to a large extent these are circumvented by using conservative design parameters and that fantastic fudge factor called the Factor of Safety.  However if we were to reduce the degree of uncertainty in a design by carrying out a proof test, then the advantages thereof need not be spelled out.  A proof test will include observations on behaviour, and may well include instrumentation.  A proof test allows the designer to choose an economical design over an ultra conservative one when ground conditions are not fully understood or construction methods are uncertain.

Then there is the issue of crisis management.  Should a crisis arise, the nature of the problem needs to be defined so that remedial measures can be implemented, and instrumentation, if correctly installed, can play a crucial role in this.

Secondly there are benefits to be had during construction, including improvements in safety for the construction workers and the public, a reduction in construction costs, greater control over construction procedures, and an enhancement of public relations, particular with regard to the very large projects which will affect the public if any crisis were to occur.  The installation and monitoring of instruments also provides legal protection in an increasingly litigious environment, indicating firstly a ‘duty of care’ to the project, including personnel, public and the client, as well as providing hard evidence should a failure occur.  And perhaps almost as importantly, by installing instruments we get to sleep easy.

We are already comfortable with the idea of instruments to remotely monitor behaviour.  A broken fuel gauge is going to eventually lead to a long hike to the filling station; a broken speedometer will lead to friendly discussions with a traffic officer and we wouldn’t dream of operating without these feedback systems.  We should apply the same philosophy to our civil engineering and mining projects.

SISGeo Geotechnical Instrumentation is officially represented by GeoZone GeoServices here in Southern Africa and as such are well placed to supply a wide range of instruments for any civil engineering or mining project.  The Italian based company designs, builds, calibrates, sells, installs and monitors instrumentation systems for use in the areas of rock and soil measurement throughout the world.

We are able to supply, install and monitor the following range of instruments:
•    Pressure Transducers
•    Inclinometers Settlement Gauges
•    Pressure and Load Cells Extensometers & Joint meters
•    Pendulums & Readouts
•    Strain Gauges & Thermometers Readouts,
•    Dataloggers & Accessories
•    Dual Height Tell Tales

We have a duty of care, perhaps a sacred trust, to ensure that our projects are designed and managed with integrity, and instrumentation can go a long way in assisting in this regard.