Numerical modelling of liquefaction tests of par- tially saturated sands in CSSLB Seyed Mohsen Seyedi Viand 1 , E.E. Eseller-Bayat 1 1. Department of Civil Engineering, Istanbul Technical University The undrained behavior of partially saturated sands under repetitive load- ing has been investigated by many researchers experimentally. The research to date demonstrate that partially saturated sands do not liquefy however, sig- nificant amount of excess pore water pressures may develop especially in loose sand specimens with degrees of saturation above 80%. Cyclic Simple Shear Liquefaction Box (CSSLB) was developed by Eseller-Bayat et al. to perform cyclic simple shear tests on large specimens using a shaking table. In this study, based on the experimental results, the behavior of loose to dense partially sat- urated sand specimens to cyclic simple shear strains under drained and un- drained conditions was modelled numerically in finite difference software pro- gram FLAC 3D (Itasca Consulting Group). The CSSLB was first modelled and the sand specimen was numerically tested under drained conditions. Then Finn and Byrne liquefaction models were used to simulate the liquefaction behavior of sands. Sand specimens with different degrees of saturation (40-83%) were tested under several cyclic simple shear strain amplitudes and the excess pore water pressures were numerically obtained. Finally, excess pore water pres- sure ratio (ru) values were compared both in numerical and experimental tests. The results were also compared with the excess pore water pressures generated in fully saturated sand specimens. Introduction Overview of Cyclic Simple Shear Liquefaction Box (CSSLB) Simple shear apparatus has been designed by number of researchers. Norwegian Geotechnical Institute Simple Shear Apparatus (NGISSA) uses cylindrical speci- mens. The Cambridge University Simple Shear Apparatus Mk7 (CUSSA Mk7) uses square shaped specimens with dimensions 10cm×10cm×2cm surrounded with fixed platens. Based on the idea of both shear apparatus stated above, Cyclic Simple Shear Liquefaction Box (CSSLB) was designed and manufactured at Northeastern Uni- versity, that allows testing large size fully and partially saturated test specimens under controlled drainage conditions (Figure 1) (Eseller-Bayat et al. (2013b)).