Instrumentation and the 15th Jennings Memorial Lecture
Well, 2017 is in full swing and it has been a busy year so far here at the GeoZone. We closed off last year on a high note – busy until the very last, and prices in for the upgrade of Kariba and the raising of the Clanwilliam Dam. So we are looking forward to positive outcomes there. Also the geotechnical consulting work has been keeping us busy and we have additionally been drilling for a couple of quarries to prove the available resources, so those two projects were more geological than geotechnical.
I see that Professor Kenichi Soga of the University of California, Berkeley , is to give the 15 Jennings Memorial Lecture on geotechnical instrumentation in Pretoria, Durban and Cape Town, scheduled for the 28th 29th and 30th March 2017 respectively.
So the question is, why instrument? Well, here is an excerpt from the notice of the talk which resonated with me and which I want to expand on a little, without of course stealing his thunder.
“Active monitoring of the construction and operational processes of geotechnical structures is essential. This implies that the structures are instrumented to assess their performance against engineering design parameters or predictive models. …..In recent years, sensor and communications research has been undergoing a revolution. Sensing is rapidly becoming part of everyday life for health, environment, security and living. There are possibilities to use emerging sensor technologies to address the needs to look after our geotechnical structures. ….Adoption of such technologies can be a catalyst for the industry to move from supply of an ‘infrastructure’ to supply of ‘whole-life support’, leading to true realization of performance based design and maintenance.’’
Taking an overview of the instrumentation industry, there does appear to be slow uptake of the new technologies by civil and geotechnical engineers. The technology is always advancing, sometimes at a frightening pace, and even in the seven years that I have been involved have seen a move towards digital outputs and a revolution in data logging. Cell phone network technology has also been a game changer, allowing remote monitoring of systems via the network.
Wearing a contractor’s hat we find that we are generally on the back foot when it comes to pricing the instrumentation for a project. Often the specifications are very open ended, which requires us to design the system architecture before we can price it, or alternatively the design has serious shortcomings which also need to be addressed before submitting a price. These problems interesting are not new, with ‘the greatest shortcoming in the state of the practice is failure to plan monitoring programs in a rational and systematic manner.’ Dunnicliff, 1993*.
Another issue is pricing. One high profile dam job we have recently been involved with was driven by price and the quality of the final installation leaves much to be desired. Initially the contractor wanted to import the cheapest instruments available, and then install them himself. At the insistence of the Resident Engineer they did eventually buy the system from us, but there was ongoing resistance to our involvement in the installation thereof. The final product speaks for itself.
Dunnicliff, (whom I mention again due to him having written the bible on instrumentation, commonly known as the red book) sums things up by saying that ‘the procurement of instruments and the awarding of field instrumentation service contracts on the basis of the lowest bid’ is a bad trend. He goes on to say that ‘if an instrumentation program sets costs above quality of instruments, or fee above experience, dedication and motivation of people, it deserves to be a failure.” Harsh words indeed but no doubt written from bitter experience.
In summary, geotechnical conditions are such that the properties of materials on or in which a structure is founded are not always perfectly understood. Exact numerical values of their properties cannot be assigned in spite of a suite of laboratory and field tests – the best we can arrive at is a range of possible values and then ‘engineering judgement’ has to come into play – generally an adoption of the worst case results or a higher factor of safety. However instrumentation can assist in removing some of the uncertainties in a design and reduce the attendant risk.
As construction progresses and geotechnical conditions monitored, the design judgements can be evaluated and if necessary updated. The monitoring therefore can form an integral part of the design process, and expanding things further to encompass the theme of the approaching Jennings Memorial Lecture, can provide ‘whole-life support.’
If you would like to receive an instrumentation brochure, please email me and I will post one off to you forthwith. The brochure covers the full gamut of instrumentation, including piezometers, strain gauges, load cells, earth pressure cells, inclinometers, extensometers, cabling and data loggers. If you need assistance specifying and designing instrumentation architecture, also please email me.