Vol. 18, No. 4 EARTHQUAKE ENGINEERING AND ENGINEERING VIBRATION October, 2019 Earthq Eng & Eng Vib (2019) 18: 811-822 DOI: https://doi.org/10.1007/s11803-019-0537-2 Numerical investigation of seismic performance of high modulus columns under earthquake loading Selçuk Demir 1† and Pelin Özener 2‡ 1. Abant İzzet Baysal University, Bolu 14030, Turkey 2. Yildiz Technical University, Istanbul 34210, Turkey Abstract: This paper presents the result of two-dimensional finite element modeling studies in order to investigate the seismic behavior of high modulus columns in liquefiable soil. Particular attention was paid to the shear stress reduction mechanism of the high modulus columns and the shear strain distribution between soil and columns during earthquake motion. Numerical analyses were performed using a nonlinear elasto-plastic model in Plaxis 2016. The reliability of the numerical simulations was verified through the results of a centrifuge test model designed to investigate the contribution of high modulus columns in liquefaction mitigation. The capability of numerical simulations was assessed primarily through comparison of predicted acceleration-time histories, pore water pressures, and displacements with the measured counterparts. The results of the numerical analysis showed that the presence of the columns did not reduce seismic shear stresses in the soil when compared to the unimproved soil condition and pure shear behavior between soil and column did not develop as expected in the current design methodology. Keywords: liquefaction; high modulus column; soil improvement; UBC3D-PLM Correspondence to: Selçuk Demir, Abant İzzet Baysal University, Bolu 14030, Turkey Tel: +090 0374 253 4640 Fax: +090 0374 253 45 58 E-mail: selcukdemir@ibu.edu.tr † PhD; ‡ Associate Professor Received January 25, 2018; Accepted November 7, 2018 1 Introduction Liquefaction is a very complex phenomenon in the geotechnical earthquake engineering field. However, the seismic behavior of soil liquefaction during earthquake loading becomes more complicated when a liquefiable soil is improved with high modulus columns (stone columns, rammed aggregate piers, jet-grout columns, unreinforced cement columns, etc.). In recent studies, this complex soil-high modulus column interaction problem has been investigated through case studies, centrifuge tests and numerical simulations (Mitchell and Wentz, 1991; Baez and Martin, 1993; Goughnour and Pestana, 1998; Adalier et al., 2003; Shenthan et al., 2004; Martin et al., 2004; Olgun and Martin, 2008; Green et al., 2008; Rayamajhi et al., 2014; Rayamajhi et al., 2015; Wismann et al., 2015; Rayamajhi et al., 2016; Tang et al., 2016; Zhou et al., 2017; Kumari et al., 2018). Currently, the seismic behavior of high modulus columns in liquefiable soils has not been extensively explored due to limited experimental results or case history data. Although there is no sufficient data from field and laboratory to draw an exact conclusion about the role of high modulus columns during liquefaction, reliable numerical methods provide valuable and useful information in order to understand the effectiveness of high modulus columns as a liquefaction mitigation method. Various high modulus columns have been used as a soil improvement technique in practice to reduce the risk of liquefaction potential and its associated hazards. The principle mechanism of these improvement methods is basically densification of the surrounding soil, reducing the generation of excess pore water pressure and decreasing the seismic shear stress of the surrounding soil (Baez, 1995). Based on the improvement mechanism that these methods provide, seismic shear reinforcement (e.g., increasing soil rigidity) may be thought to be an intersection point of these soil improvement techniques. In this study, the outcomes of a series of dynamic centrifuge model tests performed by Rayamajhi et al. (2015) were utilized to investigate the contribution of high modulus columns in liquefaction mitigation. For this purpose, dynamic centrifuge model test results were analyzed through the UBC3D-PLM model that was implemented in Plaxis by Tsegaye (2010). The numerical simulations of these centrifuge tests were then evaluated in terms of time histories of accelerations, excess pore water pressures, and displacements in order to understand the reliability of the numerical predictions. Following a verification process, the seismic shear stress and shear strain sharing mechanism that was generated between high modulus columns and the surrounding soil were investigated. The effect of high modulus columns on the reduction of liquefaction potential was explained