Liquefaction resistance of sand reinforced with geosynthetics S. Altun 1 , A. B. Go ¨ktepe 2 and M. A. Lav 3 1 Assistant Professor, EgeUniversity, Department of Civil Engineering, Bornova-Izmir, Turkey, Telephone: +90 232 3886026, Telefax: +90 232 3425629, E-mail: selim.altun@ege.edu.tr 2 Project Manager, Kolin Const Co., Akkoy Dam and HEPP, Kurtun, Gumushane, Turkey, Telephone: +90 232 3886026, Telefax: +90 232 3425629, E-mail: abgoktepe@gmail.com 3 Associate Professor, Istanbul Technical University, Department of Civil Engineering, Maslak-Istanbul, Turkey, Telephone: +90 212 2856582, Telefax: +90 212 2856582; E-mail: aglav@ins.itu.edu.tr Received 3 January 2007, revised 24 January 2008, accepted 21 February 2008 ABSTRACT: This paper describes an investigation into the performance of geosynthetics in enhancing the resistance to liquefaction of medium dense (D r ¼ 50%) sand deposits. Cyclic torsional shear tests were carried out on 99 laboratory test specimens under a confining pressure of 98 kPa and a loading frequency of 0.1 Hz. A series of shear stress ratios was used to evaluate the behaviour of sand under cyclic loading conditions. Different types of geotextile (woven, nonwoven) and different arrangements of geotextiles (one, two, three and four layers) were tested. Test results revealed that the liquefaction resistance of sand deposits can be significantly increased by geosynthetic reinforcement. Nonwoven geotextiles were found to perform better than woven geotextiles as reinforcement materials. The results indicate that both the type and the arrangement of reinforcements are crucial in increasing the liquefaction resistance of medium dense sands, and there can be significant variations in the behaviour, depending on the arrangement of the reinforcement. KEYWORDS: Geosynthetics, Liquefaction, Cyclic torsional shear, Geotextiles, Sand REFERENCE: Altun, S., Go ¨ktepe, A. B. & and Lav, M. A. (2008). Liquefaction resistance of sand reinforced with geosynthetics. Geosynthetics International, 15, No. 5, 322–332. [doi: 10.1680/gein.2008.15.5.322] 1. INTRODUCTION The rate and the degree of porewater pressure build-up and the strength of soil under cyclic loading conditions depend primarily on factors such as the number of cycles, amplitude, period and duration of the different cyclic loading components, the soil characteristics (rel- ative density, mean particle size, degree of saturation), and the drainage (geologic profile, soil stratigraphy), along with the initial effective confining pressure within the soil deposits (Seed 1979; Diyaljee and Raymond 1982; Giroud and Han 2004). Soil loses its strength with increasing excess porewater pressure. Eventually, saturated uniformly graded sands and gravels liquefy, leading to extensive damage to structures supported on such soils. This type of failure has sparked the interest of many researchers in the field, and significant work has been carried out to investigate liquefaction risk (Faccioli 1973; Christian and Swiger 1975; Finn et al. 1977; Haldar and Tang 1979; Seed 1979; Oka et al. 1981). Geotextiles are basically used for five main functions: separation of layers, earth reinforcement, filtration, drai- nage, and containment. Many researchers have investi- gated the effects of geotextile utilisation on dynamic response of soils (McDougal and Sollitt 1984; Seitz and Kany 1986; Vercueil et al. 1997; Das 1998; De and Zimmie 1998; Floss et al. 1990; Kothari and Das 1994; Tan et al. 1998; Hammeri and Fannin 1999; Chew et al. 2000). Most of these studies conclude that the use of geotextiles dramatically improves the dynamic properties of soils. In addition, Krishnaswamy and Isaac (1994, 1995) concluded that such reinforcement also reduces the liquefaction potential of granular soils. Krishnaswamy and Isaac (1994, 1995) suggested the use of geotextiles to increase the effective confining pressure and eliminate liquefaction. Other researchers may not have preferred this method because the place- ment of geotextiles layers in depth requires some earth- work to be done. First, the soil is excavated, then geotextiles are placed at the base of excavation and the soil is recompacted to a density greater than 95% of either maximum Proctor or relative density. The higher Geosynthetics International, 2008, 15, No. 5 322 1072-6349 # 2008 Thomas Telford Ltd