Effect of Non-Plastic Fines on Liquefaction Resistance and Pore Pressure Behavior of Fine Sand

Effect of Non-Plastic Fines on Liquefaction Resistance and Pore Pressure Behavior of Fine Sand

C. Hanumantharao (K L University, India) and G. V. Ramana (Indian Institute of Technology Delhi, India)
Copyright: © 2011 |Pages: 14
DOI: 10.4018/jgee.2011070105
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The liquefaction behavior of sand-silt mixtures is highly debatable. Various conflicting opinions are prevalent in literature, as no unique test parameter exists that can be used to express the effect of non-plastic fines on liquefaction resistance of sand. Thus, the present study critically reviews and summarizes the effect of non-plastic fines on liquefaction resistance of sand along with the test parameter and the range of fines contents used to arrive at the given conclusion. In addition, several stress controlled cyclic triaxial tests were conducted on fine Yamuna sand with varying percentages of non-plastic silt. In the current study, relative density has been adopted as the standard test parameter, as it can be directly correlated to the standard penetration value in the field. Results shows that if non-plastic fines are added to sand, liquefaction resistance increases below the limiting silt content and then liquefaction resistance decreases as further addition of fines when relative density is constant. As long as the fines are non-plastic, the pore pressure behavior is similar to that of sands and can be represented with the simple models.
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1. Introduction

Liquefaction has become one of the most interesting, complex and controversial topic of research for geotechnical engineers, especially after the Alaska and Nigata earthquakes in 1964. Most of the earlier studies on liquefaction have focused on clean sands containing little or no fines. However, a number of case histories have revealed that silty sands are also prone to liquefaction (Kuribayashi & Tatsuoka, 1975; Seed et al., 1983; Chang, 1990; Yamamuro & Lade, 1998). Recent laboratory test results have demonstrated that silty sand/sandy silt is more liquefiable than sand (Vaid et al., 1990; Baziar & Dobry, 1995; Lade & Yamamuro, 1997; Zlatovic & Ishihara, 1997; Yamamuro & Lade, 1998; Amini & Qi, 2000; Xenaki & Athanasopoulos, 2003).

Despite these numerous reported results, the effect of non-plastic fines on liquefaction resistance is not very well understood as the problem lies in the fact that the reported results are conflicting and full of ambiguous. While several researchers (Dezfulian, 1982; Tokimatsu & Yoshimi, 1983; Seed et al., 1983; Kuerbis et al., 1988; Chang, 1990; Pitman et al., 1994; Amini & Qi, 2000) reported that increasing the fines content increases the liquefaction resistance, other researchers also reported that increasing the fines content decreases the liquefaction resistance (Shen et al., 1977; Troncoso & Verdugo, 1985; Troncoso, 1990; Lade & Yamamuro, 1997; Yamamuro & Lade, 1997; Zlatovic & Ishihara, 1997).

Effect of non-plastic silt on liquefaction resistance of sand is better understood in terms of sand skeleton/ intergranular void ratio rather than silt content (Shen et al., 1977; Troncoso & Verdugo, 1985; Kuerbis et al., 1988; Vaid, 1994; Polito & Martin, 2001; Xenaki & Athanasopolous, 2003). When clean sand is mixed with non-plastic silt, the maximum and minimum void ratios as well as the range of void ratios change and highly unstable and compressible particle structures may formed in loose deposits (Lade & Yamamuro, 1997; Yamamuro & Lade, 1997). Some of the specimens tested by Shen et al. (1977) had skeleton void ratios lower than the minimum void ratio of the specimen. Shen et al. (1977) also reported that, the trend of cyclic strength with respect to density changed markedly as the silt content exceeded 20%, an observation that is consistent with the postulated change in fabric at this value of fines content.

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