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Note: This is a reprint of an article originally published by Civil + Structural Engineer
Any engineer familiar with how foundations act in earthquake-prone areas can tell you one thing: Liquefaction — when seismic activity causes soils to act more as a liquid than a solid — can cause serious damage to otherwise safe and sturdy structures. Structural damage to a building is an obvious (and disastrous) result of severe earthquakes; however, liquefaction can be just as dangerous and a lot less obvious. If the soil supporting a building’s foundation softens, the base will likely fail. At best, this will cause a building to settle, and at worst, could cause it to collapse.
However, much in the same way that buildings can be built to better withstand earthquakes, the effects of liquefaction can be mitigated or prevented altogether. Addressing them starts with proper preparation and testing.
What we know
Most commercial engineers working in seismically active areas are already familiar with grain particle analysis, which typically predicts the severity of possible liquefaction within a foundation. In fact, the International Building Code makes such analysis and preparation for liquefaction mandatory.
The same, however, can’t be said for residential structures. The International Residential Code doesn’t require liquefaction to be accounted for, meaning it’s often overlooked or ignored to save time or money.
There’s no question that forgoing liquefaction analysis in earthquake-prone areas is risky, especially in vulnerable residential buildings built on shallow foundations. The problem for many developers is that the cost of prevention outweighs the potential costs associated with damages due to liquefaction.
A major reason liquefaction prevention is so costly pertains to the fact that its consequences in any given situation are hard to predict. Liquefaction can cause damage in a variety of ways, from flow failures to settling to a loss of load-bearing strength. Forecasting potential problems before it’s too late isn’t always possible, but as a result, prevention techniques are overly broad and not cost-effective.
Where we go from here
Scale-model research exists, but questions always arise on how to extrapolate those results toward full-scale deep foundations. To truly see all the effects, you would have to trigger an earthquake, which isn’t exactly a tantalizing proposition.
Recently, researchers have begun to work with experimental methods, such as blast-induced liquefaction, that some believe can simulate the effects of seismic events on full-scale deep foundations. For instance, a deep foundation study conducted by the University of Arkansas that was focused on the New Madrid Seismic Zone deepened our understandings of the effects of liquefaction in specific contexts.
Findings such as these will increase our understanding of how deep foundations, such as helical piles, behave during earthquakes. The more knowledge engineers have, the more that information can be applied to provide baseline solutions at a reasonable cost.
The research will allow engineers to provide specific materials and methods that have proven to work based on the research. In other words, instead of a one-size-fits-all solution, engineers will be able to implement tailor-made solutions that will be not only more effective, but also easier on the wallet.
Engineers must become more familiar with these studies and keep up with the advancements in scale-model research of liquefaction’s effects. If these experimental methods prove reliable, predicting the effects of liquefaction will become much more feasible. As a result, foundations will be more resilient, and developers may be able to save themselves a lot of time and money in the process.
Gary L. Seider, P.E., is engineering manager of CHANCE® Civil and Utility Helical Products. Hubbell Power Systems Inc.manufactures a wide array of transmission, distribution, substation, OEM, and telecommunication products used by utilities.
With four U.S. patents and more than 40 years of industry experience, Seider oversees the company’s civil construction and utility application/project engineering staff. His team assists owners, engineers, and contractors with technical assistance, guidance, and recommendations for the proper use of CHANCE Helical Anchors and piles and Atlas Resistance® products.
by Gary L. Seider