Evaluating Liquefaction-Induced Lateral Deformation of Earth Slopes using Computational Fluid Dynamics (CFD) Computational Fluid Dynamics (CFD) Yaser Jafarian Department of Civil Engineering, Semnan University, Semnan, Iran. Ali Ghorbani Faculty of Engineering, Guilan University, Rasht, Iran. email: Omid Ahmadi International Branch, Guilan University, Rasht, Iran. SUMMARY: Liquefiable soils within earth slopes are prone to lateral deformation, which is a cause of significant damage in earthquakes. In the recent decade, researchers have presented studies in which liquefied soils is considered as viscous fluid. In such manner, the liquefied soil behaves as non-Newtonian fluid, whose viscosity decreases with increasing shear strain rate. The current study uses computational fluid dynamic to predict liquefaction-induced lateral deformation of an infinite earth slope. Post-liquefaction residual strength of soil is incorporated to estimate Bingham viscosity within an Incremental Elastic Model. An iterative scheme is presented to estimate strain-compatible soil stiffness. Centrifuge model tests are numerically simulated in this study to validate the numerical simulation. The results, which are considered in terms of the displacements of the liquefied soil masses, confirm that the computed and the measured soil displacements are in agreement within a reasonable degree of precision. Keywords: liquefaction, lateral spreading, computational fluid dynamics 1.INTRODUCTION Liquefaction of loose and saturated soil deposits has produced catastrophic failures during the earthquakes. This phenomenon produces disastrous consequences such as lateral spreading in free-face and gently sloping grounds. Liquefaction-induced lateral spreading has caused massive damages to deep foundation of buildings and bridges, embankments and lifeline systems. During the 1964 Niigata earthquake, lateral movement of liquefied soils resulted in considerable bending and failure of pile systems. In the same year, wide spread lateral ground deformations were observed for more than 250 bridges and embankments along the Alaskan railroads and highways. Several methods have been presented in the literature to predict the displacements produced by liquefaction-induced lateral spreading. They can be classified into the following groups: (1) empirical, (2) numerical, and (3) simplified analytical methods. Researchers have carried out numerical study to simulate behavior of liquefied soil as a reduced-stiffness solid. Based on this assumption, Yasuda et al. (1992) proposed a simple static finite element analysis in two stages to assess the lateral spreading. In this approach, the stress regime in the ground is calculated using the elastic modulus before shaking starts and then the stresses are held constant and analysis is conducted again using the shear modulus decreased due to liquefaction. By the principle of minimum potential energy, Towhata and Orense (1992) proposed a three dimensional finite element approach to predict the permanent displacements. By assuming the liquefied soil as a visco-elastic material, Aydan (1995) proposed a finite element approach based on an adaptive mesh technique. Moreover, Uzouka et al. (1998) developed a numerical method to predict lateral spreading of liquefied soil based on fluid dynamics. They used a numerical method by assuming liquefied soil as a Bingham fluid. Hadush et al. (2001) employed cubic