Behavior of EPS geofoam in stress-controlled cyclic uniaxial tests Aurelian C. Trandafir a, * , Steven F. Bartlett b , Bret N. Lingwall b a Department of Geology and Geophysics, Geological Engineering Program, University of Utah,115 South 1460 East Rm 383, Salt Lake City, UT 84112-0101, USA b Department of Civil and Environmental Engineering, University of Utah,122 South Central Campus Dr., Salt Lake City, UT 84112, USA article info Article history: Received 7 May 2009 Received in revised form 21 December 2009 Accepted 1 January 2010 Available online 18 February 2010 Keywords: EPS geofoam Static deviator stress Stress-controlled cyclic uniaxial tests Dynamic properties abstract During recent years, increasing consideration has been given to the compressible inclusion function of EPS geofoam, which makes this cellular geosynthetic an ideal material for reducing the static and seismic lateral earth pressures against rigid non-yielding retaining structures. Although the behavior of EPS geofoam under monotonic loading conditions has been extensively studied using laboratory triaxial compression tests, little research has been done until present on the cyclic stress–strain behavior of this material that is essential for optimizing and improving the seismic buffer function of EPS geofoam in geotechnical earthquake engineering applications. In this context, the present paper summarizes the results of a laboratory study based on stress-controlled cyclic uniaxial tests on EPS samples with various initial (static) deviator stresses. The experimental results indicate a somewhat different dynamic response of geofoam compared to the currently published relationships obtained from strain-controlled cyclic tests. Data from stress-controlled cyclic uniaxial tests show a logarithmic decrease in the damping ratio of EPS geofoam with increasing axial strain amplitude. Furthermore, for cyclic axial strain ampli- tudes greater than about 0.87–1.0%, the material exhibited a visco-elasto-plastic behavior associated with the occurrence of permanent plastic strains at the end of the cyclic tests. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The block-molded expanded polystyrene (EPS) geofoam is a type of cellular geosynthetic with a long history of successful applications in geotechnical engineering. The use of EPS geofoam dates back to the 1960s when the Norwegian Road Research Laboratory employed the lightweight-fill function of this material to build road embankments over soft soils. Since then, EPS geofoam has become the material of choice in a variety of geotechnical problems requiring lightweight-fill such as in slope stabilization (e.g., Elragi, 2000; Jutkofsky et al., 2000; Sheeley, 2000; Negussey, 2002; Srirajan, 2001), embankments (e.g., Refsdal, 1985; Aaboe, 1987; Magnan and Serratrice, 1989; Duskov, 1991; Frydenlund, 1991; Frydenlund and Aaboe, 1996; van Dorp, 1996; Elragi, 2000; Zou et al., 2000; Negussey et al., 2001; Newman et al., in press), earth retaining structures (e.g., Negussey and Sun, 1996; Elragi, 2000), bridge approaches and bridge abutments (e.g., Williams and Snowdon, 1990; Skuggedal and Aaboe, 1991; McDonald and Brown, 1993; Elragi, 2000; Abu-Hejleh et al., 2003), buried pipes (e.g., Elragi, 2000), etc., due to its extremely low density normally ranging within 12–39 kg/m 3 . During recent years, increasing consideration has been given to the compressible inclusion function of EPS geofoam associated with its high compressibility, which makes the geofoam an ideal mate- rial for reducing the static and seismic lateral earth pressures acting on rigid non-yielding retaining walls (e.g., below grade building walls, bridge abutments, or restrained walls). The basic concept of compressible inclusion function for the static case has been outlined by Horvath (1997, 2008), and involves the inclusion of a compressible material representing the least-stiff component of a multi-material geotechnical system. The application of the compressible inclusion function of the EPS geofoam to rigid retaining walls consists of placing a relatively thin geofoam layer between the wall and the retained soil (Fig. 1). Due to its low stiffness, the geofoam will undergo horizontal compression and will allow for a certain lateral deformation of the retained soil mass (i.e., controlled yielding) thus mobilizing the soil shear strength and bringing the soil mass close to the active failure state. The result is a reduction in the lateral earth pressures against the wall, as they will approach the minimum value characterizing the active state. Field scale experiments demonstrated the significant role of the compressible inclusion function of geofoam in reducing the lateral earth pressures against rigid non-yielding retaining walls (Partos and Kazaniwsky, 1987). The effectiveness of EPS geofoam in reducing the static lateral load against a vertical rigid non-yielding retaining wall is also * Corresponding author. Tel.: þ1 801 5850491; fax: þ1 801 5817065. E-mail addresses: atrandafi[email protected], a.trandafi[email protected] (A.C. Trandafir). Contents lists available at ScienceDirect Geotextiles and Geomembranes journal homepage: www.elsevier.com/locate/geotexmem 0266-1144/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.geotexmem.2010.01.002 Geotextiles and Geomembranes 28 (2010) 514–524
Behavior of EPS geofoam in stress-controlled cyclic uniaxial tests
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