We continue to build progressively more seismically resilient structures, but there’s always more we could do. New research done by Dr. Amy Cerato at Oklahoma University supports the use of helical piles. She has demonstrated that these piles outperform conventional materials in dry sand. Her data can be found here, and it is compelling. There are YouTube videos of the testing as well. Of course, there is more work to be done. I for one would like to see more testing done with a greater sample size, a stronger comparison to the performance of conventional materials, and tests where beds are not reused. While these and other critiques do exist, this study clearly moves the needle forward in an exciting way. Helical piles are widely used in other countries in high seismic activity zones. The US has been slow to adopt these, waiting for conclusive evidence such as this to prove the case for them.
This brings up 2 valuable points. The first is a question of risk. How much data do we need before we adopt new technologies? This applies broadly across industries, and I’ll leave that for you to consider on your own. No matter where you fall on the spectrum, however, it is safe to say that more data is generally preferred. In this case, I came away convinced that these devices can provide improved stability and vibration isolation during seismic events. This brings me to the second point to which I refer, how to get that data most effectively.
There are two means of obtaining additional data in this (and most) cases, test or analysis / simulation. More testing would be wonderful, but it’s expensive, time consuming, and logistically challenging. Additionally, as is so often the case, pile design optimization by test would be necessary to achieving results that are highly representative of reality. In a surprise to no one, perhaps, I’d advocate that the design be optimized by simulation. The twist here is that mechanical engineers should be heavily involved along side civil engineers in a closely tied interdisciplinary endeavor.
This is very much a case of “aces in their places”. While there is overlap between these fields, the areas of peak expertise are different. Mechanical engineers should be employed broadly to build the case for helical piles and specifically to design helical piles for different applications either by code or on a case by case basis. Civil engineers have substantial experience in designing with structural materials and one might be tempted to employ them exclusively in this work. However, in this instance, I’d call on mechanical engineers to assist. There are helical steel plates of varying pitch, spacing, thickness, and diameter. These are welded to metal cylinders of varying length and diameter. There are issues of vibration damping, metal fatigue, corrosion, stress corrosion cracking, weld fatigue, abrasion, buckling, bending, and all manner of condition that mechanical engineers spend their entire professional lives focused on. Even the seismic vibration inputs are nothing more than the random vibration power spectral density curves normally experienced by aircraft components. If the design is not well optimized, the test results can be misleading, and simulation can allow for this optimization in a fraction of the time and at a fraction of the cost.
Helical piles demonstrate promising potential to enhance seismic resilience of structures. Dr. Cerato’s work adds valuable data to the argument in their favor. More work to build the case for helical piles generally, and careful design optimization on a case by case basis would help. Mechanical engineers are well suited for this work, much of which can be done by simulation. There are many examples of mechanical and civil engineers working well together in close collaboration, and this is yet another example of an instance in which it would be beneficial.