Soil liquefaction occurs when saturated soils lacking cohesion, such as sands, lose strength and stiffness after cycles of earthquake-induced loads. A buildup of pore water pressure reduces the effective stress holding soil particles together, sometimes causing the soil to behave and flow like a liquid.
The likelihood of liquefaction occurring is influenced by several factors, including soil grain characteristics, density, and, importantly, initial stress condition. Among these, the effective confining stress (or overburden stress) is a key parameter, as it directly affects the cyclic resistance of the soil. Laboratory studies have shown that the cyclic resistance ratio, a normalized measure of a soil’s resistance to liquefaction, tends to decrease as the effective confining pressure increases, making an evaluation of overburden stress effects vital for an accurate liquefaction assessment.
In “Evaluating the Effects of Overburden Stress on Soil Liquefaction: Insights from Cyclic Test Data,” researchers Brian Carlton, Kristin J. Ulmer, Paolo Zimmaro, Kenneth S. Hudson, Scott J. Brandenberg, Jonathan P. Stewart, and Steven L. Kramer address this critical topic by analyzing the largest dataset to date of overburden stress correction factor values, which are used to adjust the CRR for different confining pressures. This study is important because traditional field case histories often focus on shallow soils, leaving the effects of higher confining stresses less well understood. By compiling and evaluating a broad range of laboratory cyclic test data, the authors propose a new model that shows less dependence on confining pressure and relative density than existing models. For practicing engineers, these findings provide a more robust basis for evaluating liquefaction potential in diverse site conditions, supporting safer and more resilient infrastructure design in earthquake-prone areas. Read the full paper in the Journal of Geotechnical and Geoenvironmental Engineering at https://doi.org/10.1061/JGGEFK.GTENG-14057. The abstract is below.
Abstract
This study investigates the effect of overburden stress (effective confining stress) on liquefaction triggering using the largest cyclic test dataset ever applied to this crucial topic. The dataset includes 225 overburden stress correction factor (𝐾𝜎) values derived from a wide range of confining stresses, relative densities, and fine contents. Our analysis reveals that specimen preparation methods, particularly tamping and compaction, significantly affect 𝐾𝜎 values. Compaction stresses due to tamping and compaction induce an overconsolidation ratio that changes with confining pressure, which may produce a larger apparent effect of confining pressure on 𝐾𝜎. We propose a new model for estimating 𝐾𝜎 for clean, normally consolidated sands, which shows less dependence on confining pressure and relative density than existing models. The effect of fines content on 𝐾𝜎 could not be isolated from other effects because fine-grained specimens in prior research were generally prepared using tamping and compaction methods. The proposed 𝐾𝜎 model is intended to isolate the effect of overburden stress, enabling its use in liquefaction triggering models where different effects are accounted for by distinct correction factors.
Explore this new approach to evaluating soil stability and how your geotechnical planning might benefit in the ASCE Library: https://doi.org/10.1061/JGGEFK.GTENG-14057.
