PRESIDENT’S MESSAGE The Value of Case Histories C ase histories are great. They are interesting to listen to, they share valuable information and experience, they tell a great story and the pictures are always awesome. However, underlying all of this is the fact that they are one of the most important tools to the geotechnical engineer and to all civil works. In our business, we do not have the benefit of testing a design before imple- mentation. Everything we construct is a one off. Mulligans (second chances to perform an action) can’t be tolerated; as history teaches us, mistakes can lead to catastrophic accidents and sometimes death. The path to managing this risk started some time ago. The greatest geotechnical engineer in history, Karl Terzaghi, was an avid user of case histories to study problems, deduce cause-and-effect and then test his hypo- thesis on the next project. His concept of effective stress, which revolutionised geotechnical engineering and solved previously inexplicable problems, was developed fully based on studying past case histories and proving the theory on new projects. He learned that a combination of investigation, prediction and measurement provided the best means to manage his risk. As a result, over many decades, Terzaghi and Peck developed the Obser- vational Method. Can you imagine another engineering discipline stating: “Let’s start building this and then adjust the parameters and the Note to Editor: Gary L. Seider, P.E., engineering manager at Hubbell Power Systems, Inc. | Chance , wrote a note to the editor regarding the article “Emergent Grout Pile Technologies” by Howard A. Perko, Ph.D., P.E., Magnum Piering, in the Mar/Apr 2019 issue. In the section “Selecting a Grout Pile,” near the end of the second paragraph, Perko ® relates his experience that the grout take of gravity-grouted helical piles diminishes with increasing depth, which sets a practical limit on the maximum depth. However, it has been my experience that the grout take actually increases with depth in most soils, where the grout mix and displacement mechanisms are key factors preventing squeeze of the hole during installation. Furthermore, gravity grouting using the Vickars method have been performed to depths in excess of 120 ft (36.6 m). DEEP FOUNDATIONS • MAY/JUNE 2019 • 7 design as we go to suit what we observe!”? How do you price that? Why do we, as geotechnical engineers, deem this reasonable or even state of the art? The reason lies in our pre- dicament — prior to commence- ment of construction, at best, we are granted the opportunity, budget and schedule to test a small sample of the soil materials we are forced to work within. As a result, we have an incomplete knowledge of discrete points within our soil matrix. What is worse is that what we can measure (local- ised) doesn’t represent the behaviour of the whole (bulk) and, often, is not at represen- tative conditions (stress, pore water pressure, etc.). The result is like a pin hole [email protected] Matthew Janes, M.B.A., P.Eng. President We have no test cases in geotechnical works, so we must learn from ourselves and from others. camera’s view of the world. An equivalent would be to engage a structural engineer to design a skyscraper using a great big pile of beams from which they could only measure and test two? Imagine the redundancy. This predicament further implies the value of high-quality monitoring. Build, measure the outcome, back calculate and finally arrive at the true engineering parameters of your building materials. This process improves and corrects our under- standing of geotechnique and prepares us for the next project. One of the most compelling aspects of measurements is that they are not factored. The data tells us the truth. Monitoring tells us the accuracy of our assum- ptions, meager testing and predictions. Most impor- tantly, monitoring reveals the performance and properties, not of our structures (e.g., struts or piles), but of the bulk soil matrix interacting with those structures. Back to Mulligans and one-offs: assessing and man- aging risk is a big topic today. Why does risk exist? It exists because of unknowns. Replacing unknowns with knowns obliterates risk. Geotechnical site investigation combined with quality monitoring and the discipline to build and share a library of case histories results in knowledge, understanding and risk reduction that can be applied to future projects. We have no test cases in geotechnical works, so we must learn from ourselves and from others. When I attend DFI meetings and witness the far ranging and excellent quality case histories presented, it reinforces my belief that DFI provides the optimum venue for just such sharing and learning. “Experience is simply the name we give to our mistakes.” Oscar Wilde
