Contents lists available at ScienceDirect Geotextiles and Geomembranes journal homepage: www.elsevier.com/locate/geotexmem Shaking table tests on geosynthetic encased columns in soft clay C. Cengiz a,* , E. Guler b a Research Associate in University of Bristol, United Kingdom b Professor in Bogazici University, Turkey ARTICLE INFO Keywords: Geosynthetics Geosynthetic encased column Ordinary stone column Shake table test Laminar box Sinusoidal loading Earthquake loading ABSTRACT This paper presents the results of an experimental research on the behavior of geosynthetic encased stone col- umns and ordinary stone columns embedded in soft clay under dynamic base shaking. For this purpose, a novel laminar box is designed and developed to run a total of eight sets of 1-G shaking table tests on four different model soil profiles: Soft clay bed, ordinary stone column installed clay bed, and clay beds with geosynthetic encased columns with two different reinforcement stiffnesses. The geosynthetic encased columns are heavily instrumented with strain rosettes to quantify the reinforcement strains developing under the action of dynamic loads. The responses of the columns are studied through the deformation modes of the encased columns and the magnitude and distribution of reinforcement strains under dynamic loading. The response of the granular in- clusion enhanced soft subsoil and embankment soil and the identification of the dynamic soil properties of the entire soil body are also discussed in this article. Finally, to determine the effect of dynamic loading on the vertical load carrying capacity, stress-controlled column load tests are undertaken both on seismically loaded and undisturbed columns. 1. Introduction Growing demand on infrastructure projects and scarcity of land in urban areas are forcing many embankments to be built on soft soils. When the area of interest is in a seismically active zone, combined ef- fects of soft soil conditions and seismic hazard constitute an unfavor- able design scenario where advanced engineering measures should be taken. Conventional piles are often used to mitigate the effects of seismic loading on the structure that are underlain by soft clays. Zhang et al. (2016) has run centrifuge tests on a 4 × 3 pile-raft system em- bedded in soft kaolin clay bed to study the bending moments occurring on the piles due to seismic loading and the response of the raft under seismic excitation. Banerjee et al. (2014) has examined the seismic ef- fects on piles installed in soft clays by means of centrifuge tests and numerical modeling. While the literature on seismic behavior and performance of foun- dation systems with piles is plentiful, geosynthetic encased columns (GECs) received little attention as a countermeasure against seismic loading. Recently, the prospect of utilizing stone columns for enhancing the rocking foundation systems' performance has been investigated by (Liu and Hutchinson, 2018). GECs have proven themselves to be a cost efficient soft soil remediation technique for supporting superstructures with flexible and rigid foundations. Small scale laboratory tests (e.g., Black et al., 2007; Murugesan and Rajagopal, 2010; Ali et al., 2014; Debnath and Dey, 2017; Hasan and Samadhiya, 2017; Miranda et al., 2017; Ghazavi et al., 2018; Mazumder et al., 2018; Chen et al., 2018; Das Amit and Deb, 2018) and field tests (Yoo and Lee, 2012; Almeida Marcio et al., 2015) have demonstrated the benefits of installing GECs to withstand vertical loads. The available literature on GECs rarely extends beyond the study of GECs subjected to static vertical loads. The exceptions to this are the studies conducted by Murugesan and Rajagopal (2009) and Mohapatra et al. (2016) where model ordinary stone columns (OSCs) and GECs embedded in sand are sheared in large scale direct shear type appa- ratus. Building on the experimental work on large scale direct shear apparatus, Mohapatra and Rajagopal (2017) have numerically mod- elled the shear behavior of GECs by making use of a finite difference software. Further, Mohapatra and Rajagopal (2017) have modelled the entirety of an embankment supported by GECs. Guler et al. (2014) have run a series of finite elements analysis utilizing DIANA to investigate the performance of OSCs and GECs under the action of seismic loads. The analysis has shown that GECs prevented excessive settlement of the superstructure. Tai et al. (2017) have studied the time-dependent clogging behavior of a stone column interacting with the surrounding host unit cell soil. Deb and Behera (2017) have mathematically mod- elled granular column installed soft ground by considering the https://doi.org/10.1016/j.geotexmem.2018.07.009 Received 14 April 2018; Received in revised form 7 July 2018; Accepted 10 July 2018 * Corresponding author. E-mail addresses: c.cihancengiz@gmail.com (C. Cengiz), eguler@boun.edu.tr (E. Guler). Geotextiles and Geomembranes 46 (2018) 748–758 0266-1144/ © 2018 Elsevier Ltd. All rights reserved. T