Research reveals new insights into soil liquefaction during earthquakes
Soil liquefaction is a natural hazard that commonly occurs during earthquakes and is one of the most catastrophic earthquake-related phenomena. During and after liquefaction, buildings and infrastructures sink, float and tilt, ground might spread and crack, settle, or initiate a landslide. Liquefaction damage often leads to extensive human casualties, destruction of lifelines, and economic losses that may result in the complete abandonment of formerly inhabited areas, posing a significant challenge to community resilience.
In a new study, the conventional understanding of soil liquefaction is being challenged, significantly reshaping our comprehension of earthquake-related soil deformation. Traditionally, soil liquefaction has been linked to undrained conditions near earthquake epicenters, but this research reveals that liquefaction can take place under drained conditions, even at considerably lower seismic-energy density levels. This discovery sheds new light on far-field liquefaction events that have long perplexed scientists. The study highlights how seismic shaking, even in drained conditions, triggers interstitial fluid flow within the soil, leading to the accumulation of excess pore pressure gradients and the subsequent loss of soil strength. Drained liquefaction unfolds rapidly, guided by the propagation of a compaction front, with its speed determined by the rate of seismic-energy injection. These findings mark a profound shift in our understanding of soil liquefaction, empowering us to conduct more precise assessments of its potential and associated risks, ultimately bolstering efforts in earthquake engineering and preparedness.
New research conducted by Dr. Shahar Ben-Zeev and Prof. Einat Aharonov at The Hebrew University of Jerusalem and the University of Strasbourg, Prof. Liran Goren of Ben-Gurion University of the Negev, and Prof. Renaud Toussaint from the University of Strasbourg has unveiled a remarkable discovery – liquefaction can occur under drained conditions even at remarkably low seismic-energy density levels.
The study, titled “Drainage explains soil liquefaction beyond the earthquake near-field" was published Wednesday in Nature Communications.
Traditionally, liquefaction has been understood as a predominantly undrained process that occurs under high-energy density conditions. This conventional view left many earthquake liquefaction events unexplained, particularly those occurring far from the earthquake epicenter, where energy density is significantly lower.
Their findings demonstrate that liquefaction can indeed occur under drained conditions, even at low seismic-energy density levels. Seismic shaking, under drained conditions, facilitates interstitial fluid flow within the soil, leading to the development of excess pore pressure gradients and subsequent soil strength loss. Drained liquefaction occurs rapidly and is influenced by the rate of seismic-energy injection.
These findings have important implications for our understanding of soil liquefaction. By considering soil liquefaction under a spectrum of drainage conditions, the researchers can now more accurately assess its potential and associated hazards. This research opens new doors for earthquake engineering and preparedness, assisting in the mitigation of risks associated with soil liquefaction in regions vulnerable to seismic activity.
Prof. Liran Goren of Ben-Gurion University's Earth and Environmental Sciences Department, "The ability to understand the process of soil liquefaction at the smallest scale of relative movement between individual grains allows more precise forecasts and risk assessments. These forecasts include, for example, the magnitude of ground settlement in response to liquefaction as well as the duration of the liquefaction event, which can last seconds, minutes, or even longer."
What sets this study apart is its unique combination of theoretical work, numerical simulations, and experimental validation.
Furthermore, in an era marked by a continual increase in the construction of reclaimed land and artificial islands, both highly susceptible to soil liquefaction, this research becomes even more pertinent.
As most of the past earthquakes occurred before the modern instrumental era, seismologists rely heavily on the interpretation of geological features to compile complete earthquake catalogs. This groundbreaking study fundamentally shifts our understanding of the conditions that may have caused liquefaction-related geological features, hence calling for revising the estimated earthquake magnitude calculated by standard methods.