Effect of Content and Plasticity of Fines on Liquefaction Resistance of Clayey Sand Using Cyclic Simple Shear Tests

In this study, the eect of the presence of plastic nes on liquefaction resistance of Firoozkooh sand is investigated. To this end, amounts of 5, 15, and 25 percent of two types of plastic ne (clay), namely, Kaolinite, with a plasticity index (PI) equal to 19, and Bentonite, with a plasticity index equal to 116, were added to Firoozkooh sand, and 68 stress-controlled tests were conducted using Cyclic Simple Shear (CSS) apparatus. Shear load frequency and consolidated vertical eective stress are equal to 0.1 Hz and 100 kPa in all tests, respectively. Initial liquefaction, maximum pore pressure ratio (ru), or double shear strain amplitude equal to 5%, have been considered as liquefaction criteria. In order to investigate the liquefaction resistance for each soil, at least three tests were conducted at each relative density. In summary, with the addition of plastic nes, nes content, as well as the plasticity of nes, aect liquefaction resistance. In Koalinite-containing soil, as the amount of nes increases up to 25%, the liquefaction resistance decreases continuously. In these soils, for all ne content less than 25%, the sand skeleton void ratio can be regarded as the eective void ratio. In Bentonite-containing soils, the lowest liquefaction resistance has been observed in soil that contains 5% Bentonite; therefore, 5% ne content is known as limiting Bentonite content. In these soils, ne content less than 5% sand skeleton void ratio, and ne content more than 5interne void ratio, are considered eective void ratios, respectively. According to the results, in the case of 5% nes content, the plasticity of nes does not play a major role. In the case of adding nes with dierent plasticities to one base soil, there exists an amount of nes content at which the plasticity of nes starts to have an increasing eect on liquefaction resistance. According to the results of this study, this threshold value is between 5% and 15%. By more investigation of available literature, we can narrow this range from its lower limit to 10%.