Load-deformation of piled embankments considering geosynthetic membrane effect and interface friction Tuan A. Pham Research Assistant, Lab 3SR, Universityof Grenoble Alpes, CNRS UMR 5521, Grenoble Cedex 09, France; Department of Civil Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan; E-mail: anhtuanpham2703@g.ecc.u-tokyo.ac.jp (corresponding author) Received 27 May 2018, revised 19 December 2018, accepted 22 April 2019, published 18 September 2019 ABSTRACT: The use of high-strength geosynthetics to enhance the load transfer mechanism onto columns is an established and increasingly popular technique in geosynthetic-reinforced and column-supported embankments. The main focus of this paper is to extend the existing models that describe the membrane action and soil arching with skin friction along the geosynthetic. This extension was undertaken to identify the parameters that affect the tension in the geosynthetic and assess the effect of geosynthetics on the load transfer. A general expression for the increase in load-bearing capacity due to the membrane action based on strict equilibrium conditions is also shown. The geosynthetic deformation is described assuming both circular and parabolic deformation shapes. These two deformation shapes do not result in a significantly different membrane effect. Therefore, the choice of deformation parameter is more important than the choice of deformation shape. The new method using both deformation models was combined with the Concentric Arches model of Van Eekelen and co-workers, and compared with the measurements and numerical results. A reasonable consistency is found. For the considered cases, the skin friction along the geosynthetic reduces the maximum geosynthetic deflection to 2.5 to 5.3%. This reduction becomes more important when the embankment is higher. KEYWORDS: Geosynthetics, Piled embankment, Analytical model, Interface friction, Membrane effect, Arching theory REFERENCE: Pham, Tuan A. (2020). Load-deformation of piled embankments considering geosynthetic membrane effect and interface friction. Geosynthetics International, 27, No. 3, 275–300. [https://doi.org/10.1680/jgein.19.00030] 1. INTRODUCTION Embankment construction for infrastructure projects has considerably increased over time. Unfortunately, embank- ment construction tends to occur on weak foundation soils, which is a challenge for geotechnical engineers due to the possible instability, large deformation and bearing failure. The low strength and high compressive character- istics of soft clay make ground improvement techniques necessary to increase the bearing capacity of the soft ground. Among a wide range of currently available solutions to address these issues is the use of column foundations and geosynthetic reinforcement (GR). Column foundations are commonly used to transfer the embankment loads to a load-bearing stratum below the soft ground, and the high-strength geosynthetics are used to transfer the load onto the columns. This technique is established at present and is increasingly popular to strengthen embankments over weak ground (Love and Milligan 2003; Alexiew et al. 2005; Hong et al. 2007). Due to the higher stiffness of columns relative to the soft surrounding soil, the vertical stresses are concentrated in the area over the columns, simultaneously reducing the stresses over soft subsoil. In any case, the settlement between columns is larger than directly on their tops, generating horizontal strains in the GR. Therefore, the load on the column (caps) may be increased by the vertical components of the tensile force, T , in the reinforcements (Low et al. 1994; Kempfert et al. 2004; Han and Gabr 2002; Le Hello and Villard 2009; Van Eekelen et al. 2013; Girout et al. 2018; Pham et al. 2018a, 2018b). Usually, the design procedures are divided into two steps. As a first step, the load or vertical stress distribution in the embankment is calculated without considering any GR, resulting in vertical stresses on top of the columns and on the soft subsoil in-between. For this step, several design methods have been introduced in the literature (e.g. Terzaghi 1936; Guido et al. 1987; Hewlett and Randolph 1988; Giroud et al. 1990; Low et al. 1994; BS8006 (BSI 2010); Russell and Pierpoint 1997; Geosynthetics International, 2020, 27, No. 3 1072-6349 © 2019 Thomas Telford Ltd 275 Downloaded by [ UNIVERSITY OF TOKYO] on [01/07/20]. Copyright © ICE Publishing, all rights reserved.