International Journal of Civil Engineering, Vol. 13, Nos. 3&4B, Transaction B: Geotechnical Engineering, September & December 2015 Liquefaction potential of reinforced silty sands M. Alibolandi 1 , R. Ziaie Moayed 2, * Received: July 2015, Revised: September 2015, Accepted: November 2015 Abstract In this study a series of cyclic triaxial tests were performed to examine the undrained dynamic resistance of silty sand reinforced with various arrangements of geotextile layers. The silt content of samples varies in percentage from 0, 10, 20, 30, 40 and 50%. A total of 32 laboratory cyclic triaxial tests have been performed on silty sand samples reinforced with geotextile layers in different depths. All tests were performed with 100 kPa confining pressure, subjected to an isotropic consolidated undrained (CIU) condition. The tests were conducted at a frequency of 2 Hz. Results indicate that both the geotextile arrangement and the silt content were most essential in the liquefaction potential of reinforced sands. An increase in the number of geotextile layers enhanced the cyclic resistance of reinforced samples against the liquefaction potential. It was also found that when the geotextile layer was posited near the top of the specimen (load application part) the liquefaction resistance would increase (e.g. for clean sands, the improvement of liquefaction resistance caused by the geotextile layer had a 0.2 depth, and the sample height was 5.5 times greater than the geotextile layer inserted in mid height of sample H). Based on the obtained results, effects of geotextile on liquefaction resistance decreased as fines content increased to about 33%. Further increase in the fines content however, would lead to higher in reinforcement advantages. The liquefaction improvement is more effective with a higher number of geotextile layers. The results also revealed that the reinforcement effect in FC≈33 % is at its lowest amount. Keywords: Silt content, Liquefaction, Cyclic triaxial test, Geotextile arrangement. 1. Introduction Many types of geotextile reinforced soil structures are subjected to cyclic or dynamic loading. In some of these structures, cyclic loading conditions occur continual as transportation infrastructures, soil retaining walls and reinforced soil located beneath machine foundations. In the others, dynamic loading condition may only happen during earthquakes. Dynamic loading in undrained conditions can cause a destructive phenomenon called liquefaction. According to the literature, soil liquefaction failures occur in saturated silty sands. Also, results reported by Ladd & Yamamuro [1] and Thevanayagam [2] indicate that sands deposited with silt content are much more liquefiable than clean sands. Moreover, deformation characteristics and pore pressure generation in silty samples are quite different from clean sand [3, 4]. Naeini and Baziar [5], indicate that the soil weakens as the silt content increases up to 35%, and then stronger than strengthens again; nonetheless, the clean sand remains the * Corresponding author: Ziaie@eng.ikiu.ac.ir 1 M. Sc.Graduated, Civil Engineering Department, Imam Khomeini International University, Qazvin, Iran 2 Associate Professor, Civil Engineering Department, Imam Khomeini International University, Qazvin, Iran pure silt. Investigations of Polito and Martin [6] and Baziar and Sharafi [7] confirm the aforementioned results. Monkul and Yamamuro [8] found that if the mean grain diameter ratio (D 50-sand/ d 50-silt ) of the sand grains to silt grains is sufficiently small, the liquefaction potential of the sand increases steadily with increasing fines content for the studied range (0%–20%). As D 50- sand /d 50-silt increases, the liquefaction potential of the silty sand might actually be less than the liquefaction potential of the clean sand. Sadrekarimi [9] indicates that the soil void ratio, the effective stress, and the shape and mineralogy of the fine particles can affect the liquefaction resistance of silty sands, allowing them to increase, decrease, or remain the same as the amount of fines content increases. Effects of reinforcement on liquefaction susceptibility for clean sands have been previously studied [10,11]. Chandrasekaran et al. [10] identify shear stress mobilization as a function of normal stress and friction of soil-geotextile interface. Vercueil et al. [11] conducted various tests using a cyclic triaxial instrument, on samples of saturated Huston RF sand material. Reinforced with circular sheets of geo synthetic material, this sand has a uniform particle size range of D 5o = 0.38 mm and C u =1.8 with e min = 0.648, e max = 1.041,. Tests performed with different types of geosynthetics, indicate a significant increase in liquefaction resistance for Seismic Geotechnique [ DOI: 10.22068/IJCE.13.3.195 ] [ Downloaded from ijce.iust.ac.ir on 2021-11-26 ] 1 / 8