Application of the Hilbert–Huang transform to identify the dynamic characteristics of a caisson foundation during liquefaction

Summary This paper presents the application of a Hilbert–Huang transform data processing technique in a dynamic response analysis to identify the dynamic characteristics of a caisson foundation during liquefaction. The degradation of structural modal frequencies during liquefaction under strong earthquakes directly related to a reduction in the stiffness of the soil‐foundation structure due to the loss of strength, and the nonlinearity of the liquefied soil layer always occur in a short time. Thus, the short‐duration variation of frequencies provided a good indicator for the occurrence of the liquefaction and geometric distortion of a soil foundation system during strong earthquakes and was a very important step in the structural health monitoring work of foundation structures. This study shows that the proposed approach was effective in identifying the instantaneous downshift of frequency of caisson foundation system during liquefaction. This study was based on the measured acceleration response data of a test foundation model from a 1‐G shaking table test. Additionally, 2D numerical modeling using a total stress analysis stipulated in the highway bridge specification (JRA 2002), an equivalent linear method in the liquefaction calculation of foundation, was conducted to evaluate the consistency with vibration testing.