As you probably already know, Ralph Peck is known as “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. Peck has summed things up perfectly and there is nothing more to add as to why geotechnical engineering in general, and instrumentation in particular, is so important.  But then again, some elaboration may be called for, and here is why you should instrument your project.

Instruments can assist you in assessing the in situ geotechnical conditions

Soils are difficult things to deal with. A cubic metre of soil has a mass in the region of 1.3 tonnes and 2.0 tonnes. They comprise clays, silts, sands and gravels. Clays and silts are cohesive, but prone to consolidation when loaded. Sands and gravels generally are non-cohesive and may be subject to collapse settlement and failure. Add some water to the mix and the shear strength of soils may fall dramatically. The properties of soils have been well documented over the years and this is not the place for a treatise on soil mechanics.

Rock can also pose its fair share of problems. The strength of a rock mass is derived from the shear strength of the rock material and the shear strength of the discontinuities. A highly-fractured rock will have a lower bulk shear strength than one displaying less fractures. The orientation of the discontinuities also plays a huge role in the stability of the rock when tunnelling through it, or cutting it back in a mining or civil engineering project. Rock mechanics is now a mature science and there is plenty of literature available on the subject should you feel led to learn more.

It would be a very brave person

What needs to be said at this stage is that soil and rock are natural materials that behave in fairly predictable ways, but there is always a degree of uncertainty in any geotechnical model. It would be foolhardy not to try and characterise the nature of the in situ natural materials prior to any design and it would be a very brave person who tunnels through soil, and rock for that matter, without trying to monitor the performance of the excavation in the short and long term. Similarly for very deep excavations and dams where ongoing stability is crucial.

Being the consummate professional that you are, here are a number of reasons why you should instrument your projects.

A more focussed and optimal design can be arrived at

First, there are enormous benefits to be had during the design of a project.  You can use instrumentation 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.

Allows you to choose an economical design

Second, as Peck pointed out, designs contain 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 you 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 you to choose an economical design over an ultra conservative one when ground conditions are not fully understood or construction methods are uncertain.

Third 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.

Providing hard evidence should a failure occur

Fourth, 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 should a failure occur.  The installation and monitoring of instruments also provides you with legal protection in an increasingly litigious environment, indicating firstly a ‘duty of care’ to the project, including personnel, public and the client. Fifth, by providing hard evidence should such a failure occur.  And sixth, perhaps almost as importantly, by installing instruments you get to sleep easy.

You wouldn't dream of operating without these feedback systems 

You 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 you wouldn’t dream of operating without these feedback systems.  I would suggest that you should apply the same philosophy to your civil engineering and mining projects.

GeoZone is able to design a bespoke system for you. Once that is done we can 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.

*Ralph B Peck in Geotechnical Instrumentation for Monitoring Field Performance, J Dunnicliffe, John Wiley & Sons, 1988.