RESEARCH PAPER Liquefaction potential of coastal slopes induced by solitary waves Yin L. Young Æ Joshua A. White Æ Heng Xiao Æ Ronaldo I. Borja Received: 10 September 2008 / Accepted: 7 January 2009 / Published online: 11 February 2009 Ó Springer-Verlag 2009 Abstract Tsunami runup and drawdown can cause liq- uefaction failure of coastal fine sand slopes due to the generation of high excess pore pressure and the reduction of the effective over burden pressure during the drawdown. The region immediately seaward of the initial shoreline is the most susceptible to tsunami-induced liquefaction fail- ure because the water level drops significantly below the still water level during the set down phase of the draw- down. The objective of this work is to develop and validate a numerical model to assess the potential for tsunami- induced liquefaction failure of coastal sandy slopes. The transient pressure distribution acting on the slope due to wave runup and drawdown is computed by solving for the hybrid Boussinesq—nonlinear shallow water equations using a finite volume method. The subsurface pore water pressure and deformation fields are solved simultaneously using a finite element method. Two different soil consti- tutive models have been examined: a linear elastic model and a non-associative Mohr–Coulomb model. The numer- ical methods are validated by comparing the results with analytical models, and with experimental measurements from a large-scale laboratory study of breaking solitary waves over a planar fine sand beach. Good comparisons were observed from both the analytical and experimental validation studies. Numerical case studies are shown for a full-scale simulation of a 10-m solitary wave over a 1:15 and 1:5 sloped fine sand beach. The results show that the soil near the bed surface, particularly along the seepage face, is at risk to liquefaction failure. The depth of the seepage face increases and the width of the seepage face decreases with increasing bed slope. The rate of bed sur- face loading and unloading due to wave runup and drawdown, respectively, also increases with increasing bed slope. Consequently, the case with the steeper slope is more susceptible to liquefaction failure due to the higher hydraulic gradient. The analysis also suggests that the results are strongly influenced by the soil permeability and relative compressibility between the pore fluid and solid skeleton, and that a coupled solid/fluid formulation is needed for the soil solver. Finally, the results show the drawdown pore pressure response is strongly influenced by nonlinear material behavior for the full-scale simulation. Keywords Coastal slopes  Liquefaction  Tsunami  Wave–seabed interaction 1 Introduction As demonstrated by the 2004 Indian Ocean Tsunami, high intensity wave runup and drawdown can lead to significant loss of lives, as well as costly damages to coastlines and coastal structures. Although there exist many studies of tsunami wave propagation and inundation modeling, few studies considered the effect of the mobile bed, and even fewer studies examined the effect of wave–seabed inter- actions in the near-shore region. During wave shoaling, Y. L. Young (&)  J. A. White  R. I. Borja Department of Civil and Environmental Engineering, Stanford University, Stanford, CA, USA e-mail: yyoung@princeton.edu J. A. White e-mail: joshua.white@stanford.edu R. I. Borja e-mail: borja@stanford.edu Y. L. Young  H. Xiao Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ, USA e-mail: xiao@princeton.edu 123 Acta Geotechnica (2009) 4:17–34 DOI 10.1007/s11440-009-0083-6