Dan Brown and Associates, PC

October 2^nd, is the day we (or at least a lot of us geoprofessionals) have all been looking forward to all year – the birthday of Professor Karl Terzaghi, The Father of Modern Day Soil Mechanics, born October 2, 1883.

Since this historic day in geotechnical engineering history falls on a Saturday this year, I offer a cheer for those of us into college football (I mean, really, who isn’t this time of year, at least in the U.S.):

Two bits, four bits, six bits..a dollar

All for Terzaghi, stand up and holler!!!!!

On the more reflective side, each year I try to find some interesting fact or quote to write about. This year, I decided to read the preface of Soil Mechanics in Engineering Practice (Terzaghi and Peck, 1948) for inspiration, and thus will quote from there:

“Unfortunately, the research activities in soil mechanics had one undesirable psychological effect. They diverted the attention of many investigators and teachers from the manifold limitations imposed by nature on the application of mathematics to problems in earthwork engineering. As a consequence, more and more emphasis has been placed on refinements in sampling and testing and on those very few problems that can be solved with accuracy. Yet, accurate solutions can be obtained only if the soil strata are practically homogeneous and continuous in horizontal directions. Furthermore, since the investigations leading to an accurate solution involve highly specialized methods of sampling and testing, they are justified only in exceptional cases. On the overwhelming majority of jobs no more than an approximate forecast is needed, and if such a forecast cannot be made by simple means it cannot be made at all.”

While our technology has allowed us to measure, analyze, test, and compute huge volumes of data, as well as investigate the highly complex nature of soil-structure systems, we sometimes get caught up in the details of precision. We try to be much more precise than the materials we work with truly allow. This is not to say we should totally throw away our technology, forsaking numerical models, design software, or sophisticated in-situ testing and return to the days of slide rules (though I can use one!). There are many times, however, that an “approximate forecast” is just as “accurate” as a calculation computed to a precise number.

So, my friends, raise your glasses this weekend to toast Professor Terzaghi and our profession!

Cheers!

Update (10/1/10): One of my (Robert’s) mentors at my first job out of grad school, Luther Boudra, P.E. at MACTEC, wrote me this morning on the subject of accuracy and precision.  I asked him if I could share his comment (and he agreed) since I thought it was very insightful:

Robert, Professors Terzaghi’s comments remind me of something I read recently in a book about precision shooting, particularly at long range.  The author, who incidentally is both an engineer and top level shooter, was noting the difference between “precision” and “accuracy”.  Precision is exemplified by being able to repeat something to close tolerance, as exemplified in the shooting community by benchrest shooters, who are primarily interested in shooting small groups of typically 5 to 10 shots.  Hitting near the center of the target, whatever it is, is of secondary importance.  Accuracy, on the other hand, requires the ability to hit what you are aiming at, precisely.  In other words to take this to our field of endeavor, it’s possible to be “precisely inaccurate”, which the various software packages available to calculate almost anything enhance the possibility of.

Speaking of slide rules, their greatest attribute is that you have to be able to estimate the answer, rather than just writing down what shows up on the display screen.