Slope Stability Due to Seismic Loading

Slope instability due to earthquakes is one of the most damaging collateral hazards. Earthquakes are the greatest threat to the long-term stability of slopes in earthquake-active regions.

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Slope Stability Due to Seismic Loading

8.1

General

Slope instability due to earthquakes is one of the most damaging collateral hazards. Earthquakes are the greatest threat to the long-term stability of slopes in earthquake-active regions. Damage from triggered landslides and other ground failures has sometimes exceeded damage directly related to strong shaking and fault rupture. Seismically triggered landslides damage and destroy homes and other structures, block roads, sever pipelines and other utility lifelines, and block stream drainages [450]. Subject to earthquake loading, the acceleration produced by the ground motions will induce cyclically varying forces on slopes, embankments, and dams. Moreover, the soil’s shear strength degrades to a certain extent (Sect. 2.1). Both effects are relevant to slopes’ instability. On the other hand, due to strain rate effects (Sect. 2.5), instant shear strength for clay soils will increase by 20–50% subject to undrained seismic loading. This increase can offset the reduction in shear strength due to an increase in soil strain. Therefore, in many cases, it is reasonable to neglect the degradation in soils’ shear strength. Four methods have been widely used to assess the slope stability subject to earthquake loading: pseudo-static analysis approach, dynamic stress-deformation analysis approach, Newmark sliding-block approach, and testing method. Pseudo-static analysis approach (Sect. 8.2) was the earliest developed method and involves simply adding a permanent body force representing the earthquake shaking to a static limit-equilibrium analysis. It is suitable for preliminary analyses and screening procedures that precede more sophisticated analyses [451]. Stress-deformation analysis (Sect. 8.3) involves a much more complex modeling of slopes by using numerical methods such as finite element method (most often), finite difference method, boundary element method, and discrete element method. In this method, the internal stresses and strains within elements are computed based on the applied gravity and seismic loads. With a dedicated modeling for © Springer International Publishing AG 2018 J. Jia, Soil Dynamics and Foundation Modeling, https://doi.org/10.1007/978-3-319-40358-8_8

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8 Slope Stability Due to Seismic Loading

stress–strain behavior of soils, this type of analysis provides a reliable prediction of mode of failure, even though this method is much more demanding with respect to soil data input and computation efforts required. This analysis method is applicable for critical infrastructures such as dams and embankments or slopes adjacent to critical lifelines or structures. The Newmark sliding-block approach (Sect. 8.4) is much more convenient than the stress-deformation analysis and yields more useful information than pseudo-static analysis, even though the Newmark sliding-block approach is slightly more complex than that of pseudo-static analysis. Subsequent modifications to sliding-block analysis have made it applicable to a wider range of landslide types [