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Intergrain contact density indices for granular mixes ¡ª II: Liquefaction resistance

S. Thevanayagam

Dept. of Civil, Struct., & Env. Eng., State Univ. of New York, Buffalo, NY 14260, USA
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Abstract: Whether the presence of non-plastic silt in a granular mix soil impact its liquefaction potential and how to evaluate liquefaction resistance of sand containing different amounts of silt contents are both controversial issues. This paper presents the results of an experimental evaluation to address these issues. Two parameters, namely, equivalent intergranular void ratio (ec)eq and equivalent interfine void ratio (ef)eq, proposed in a companion paper (Thevanayagam, 2007) as indices of active grain contacts in a granular mix, are used to characterize liquefaction resistance of sands and silty sands. Results indicate that, at the same global void ratio (e), liquefaction resistance of silty sand decreases with an increase in fines content (CF) up to a threshold value (CFth). This is due to a reduction in intergrain contact density between the coarse grains. Beyond CFth, with further addition of fines, the interfine contacts become significant while the inter-coarse grain contacts diminish and coarse grains become dispersed. At the same e, the liquefaction resistance increases and the soil becomes stronger with a further increase in silt content. Beyond a limiting fines content (CFL), the liquefaction resistance is controlled by interfine contacts only. When CF<CFth, at the same (ec)eq, the liquefaction resistance of silty sand is comparable to that of the host clean sand at a void ratio equal to (ec)eq. When CF>CFth, at the same (ef)eq, the cyclic strength of a sandy silt is comparable to the host silt at a void ratio equal to (ef)eq.

Keywords:  Sand; silt; fines; silty sand; liquefaction; cyclic strength