Role Of Soil Behavior On The Initial Kinematics Of Tsunamigenic Slides

Abstract

Recent investigations on tsunami generation from submarine mass failures show that one of the most important factors influencing the source characteristics of the wave is the initial acceleration of the failure itself. In a number of these studies, a translational slide is modeled as a rigid body sliding down an inclined plane and basal resistance is neglected. In this paper, a similar rigid body model is proposed that incorporates basal resistance, which is related to the shear strength of the soil. Initial slide kinematics were investigated under two triggering mechanisms including overpressures at depth and rapid sedimentation. The model results show that soil behavior significantly influences the acceleration time history as well as the magnitude of the peak acceleration. The slide kinematics depend largely on the initial stress state and on the undrained residual shear strength of the soil along a potential failure surface, which highlights the importance of performing detailed geotechnical site investigations when assessing these geohazards. More research is needed to determine the influence of using more realistic basal friction models on the initial wave heights generated by submarine mass failures.

The Effects of Basal Resistance and Hydroplaning on the Initial Kinematics of Seismically Induced Tsunamigenic Landslides

“…where γ = ratio of the bulk density of the sediment to the density of water, θ = slope angle, g = gravitational acceleration, B = slide length (for an equivalent semi-ellipse), C m = added mass coefficient, C n = Coulomb friction coefficient, For translational failures, Grilli and Watts (2005) and Watts et al (2005) assumed that C n was nearly zero, once motion was initiated, thus eliminating any role of soil behavior on the kinematics of the failed mass. Bradshaw et al (2007) extended Eq. 1 to include basal resistance as a function of s and B:…”

“…Given the results of undrained ring shear testing by Stark and Contreras (1996) on normally consolidated Drammen clay, the undrained residual shear strength (S ur ) is defined by the following: Based on Stark and Contreras's ring test results, Bradshaw et al (2007) modeled the complete sediment strain softening behavior from peak to residual shear strength. However, given the small displacements (~ 2 cm) required to mobilize the residual strength in this sediment, it was thought that perhaps the strength behavior could be simplified to use a constant residual shear strength for all displacements.…”

“…However, since the parameter of greatest influence on tsunami generation has been shown to be the initial acceleration of the center of the failed mass (Haugen et al 2005;Watts et al 2005; and others), elimination of basal resistance (i.e., soil behavior) may result in a potentially overestimated acceleration time history that is not representative of actual slide motion. Accordingly, Bradshaw et al (2007) developed a modified solid body model, extending the work of Grilli and Watts (2005), to include effects of basal resistance on translational failures triggered by non-seismic events (i.e., rapid sedimentation and overpressures). This paper presents a further refinement of that analysis of initial slide kinematics with a model for a seismically induced slide, that accounts for effects of basal resistance, slope angle, and hydroplaning on the time history of slide acceleration.…”