Abstract
Since liquefaction was first observed in South Korea during the Pohang earthquake, public concerns regarding the seismic stability of major infrastructure have increased substantially. However, the seismic behavior of tunnel shafts, which are an important element of tunnel structures, has not been properly established, especially under liquefiable soil conditions. In this study, 3D numerical modeling with Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) was performed to predict the dynamic behavior of a vertical tunnel shaft during liquefaction. This study demonstrates key aspects of the dynamic behavior of tunnel shafts by varying important parameters such as the thickness of the liquefiable soil layer and applied seismicity level. Moreover, important dynamic responses such as excess pore pressure generation, the seismic bending moment of the shaft, and lateral displacements are highlighted. Finally, meaningful discussion of the seismic risk analysis based on damage indices is conducted based on the analysis results.
Highlights
Liquefaction is a major cause of damage to facility structures during earthquakes; it was first observed in South Korea during the Pohang earthquake
Public concern regarding the seismic stability of major infrastructure has been increasing, and revision of the seismic design criteria for various facilities is in progress
As summarized in Kwon & Yoo (2020) [1], behavior of the soil-pile system in in liquefiable sand exhibits more complicated characteristics than that in dry soil due to the development of excess pore pressure caused by cyclic loading
Summary
Liquefaction is a major cause of damage to facility structures during earthquakes; it was first observed in South Korea during the Pohang earthquake. Schmidt and Hashash [10], Chou et al [11], Adalier et al [12], Chang et al [13], Azadi and Hosseini [14], Bao et al [15], Lee et al [16], Miranda et al [17], and Sugito et al [18] analyzed the dynamic behavior of tunnels embedded in liquefiable soil using model tests or numerical analyses These studies mainly focused on the uplifting of the tunnel under liquefaction, damage to the tunnel body, and tunnel–building interaction problems. Three-dimensional numerical modeling was performed to predict the dynamic behavior of a vertical tunnel shaft that passes through a liquefiable loose sand layer Important parameters such as the thickness of the liquefiable sand layer and input earthquake magnitude were varied and used for the analysis of 12 different cases. This study highlights the key aspects of the seismic behavior of a tunnel shaft under liquefaction, such as excess pore pressure generation and the seismic bending moment, and displacement of the shaft, and provides a meaningful discussion regarding earthquake risk assessment with damage indices based on the analysis results
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