Abstract:
Deep foundations are commonly used to prevent seismic slope instability, deriving resistance to ground movement through embedment in bearing material below the slide plane. Part I of this topic for non-seismic cases was presented as the S3 virtual webinar event last summer, and showed that many of the design methods used in practice to incorporate piles into limit-equilibrium method slope stability analysis (LEM SSA) fail to adequately capture the pile resistance mechanism or correctly identify the critical pile failure mode, leading to false interpretation of static factors of safety. Of particular concern is the common practice of assigning the shear strength of the pile material, e.g. the shear strength of concrete or steel multiplied by the cross sectional area of the pile, as a resisting force in slope stability analyses. A simple method was presented to correctly identify the controlling pile failure mechanism (shear, flexure, or rigid body rotation) using laterally-loaded pile analysis. In this Part II presentation, these concepts are extended to seismic cases, providing a unified framework for relating coseismic slope displacement, pseudostatic factors of safety, pile resistance, and pile structural demands. Examples for seismically-induced landslides and lateral spreading are presented.