عنوان مقاله [English]
In this study, the effect of the presence of plastic fines on liquefaction resistance of Firoozkooh sand is investigated. To this end, amounts of 5, 15, and 25 percent of two types of plastic fine (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 effective stress are equal to 0.1 Hz and 100 kPa in all tests, respectively. Initial liquefaction, maximum pore pressure ratio $(r_u)$, 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 fines, fines content, as well as the plasticity of fines, affect liquefaction resistance.In Koalinite-containing soil, as the amount of fines increases up to 25\%, the liquefaction resistance decreases continuously. In these soils, for all fine content less than 25\%, the sand skeleton void ratio can be regarded as the
effective void ratio. In Bentonite-containing soils, the lowest liquefaction resistance has been observed in soil that contains 5\% Bentonite; therefore, 5\% fine content is known as limiting Bentonite content. In these soils, fine
content less than 5\% sand skeleton void ratio, and fine content more than 5% interfine void ratio, are considered effective void ratios, respectively.According to the results, in the case of 5\% fines content, the plasticity of
fines does not play a major role. In the case of adding fines with different plasticities to one base soil, there exists an amount of fines content at which the plasticity of fines starts to have an increasing effect 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\%.