Assessment of Nakamura Methodology for Evaluating Soil Liquefaction Potential

Cyclic liquefaction is a phenomenon in which soil deposits formed by loose and saturated sands, lose their shear resistance due to dynamic loads, as earthquakes, sometimes causing the collapse of structures. This phenomenon is a hazard in different cities of the world, as is the case of Santiago de Cali (Colombia), a city that has large alluvial deposits due to its seven rivers. Currently, the liquefaction potential is evaluated by field tests that can be expensive and difficult to perform in densely urbanized areas. Due to this drawbacks, this paper proposes a simple and versatile methodology to evaluate the liquefaction potential in large areas based on the vulnerability index ($K_g$) proposed by Nakamura in 1997 (hereinafter Nakamura Methodology). This methodology consists of calculating the vulnerability index using the fundamental frequency ($F_g$) and amplification factor ($A_g$) determined using HVSR method. The $K_g$ index quantifies the probable damage in the soil produced by earthquakes, and for sand deposits, $K_g$ can be correlated with liquefaction potential. For this research, the liquefaction potential was evaluated using Nakamura methodology in 34 points of Santiago de Cali, within an approximate area of 12 km². The results were compared with those of SPT and CPT tests performed in the same area. The methodology showed a match of up to 82% compared to conventional methods. In conclusion, Nakamura methodology is a viable alternative for liquefaction hazard mapping of large areas and could be very useful in places where there are limited funds or the conditions for more robust testing are not available.