عنوان مقاله [English]
Earthquake-induced cyclic shear stresses may lead to a remarkable loss of shear strength, accumulation of pore water pressure, and permanent large amplitude deformations in granular soils. The technical term liquefaction is commonly attributed to the family of phenomena named above. Liquefaction of clean sands has been studied extensively in the laboratory, and in past, it used to be believed that the presence of non-plastic fines in coarse granular soils definitely eventuates in strengthening the soil structure against liquefaction. Nevertheless, Yamamuro and Lade  revealed that the majority of the catastrophic liquefaction case histories have occurred in natural and man-made silty sand alluvia. Surprisingly, the latest experimental studies have pointed out that the silty sands are very prone to flow liquefaction instability under both monotonic and cyclic shear loading scenarios. In this subject, adding non-plastic fines up to a transitional threshold within the range of 30 to 40% by weight of the total solid phase leads to a gradual decrease in both shear strength and tendency towards dilation. More recent experimental studies have reported the gradual downward relocation of the Critical State Line (CSL) with fines content in void ratio vs. mean principal effective stress (i.e., e vs. p) plane for fines contents lower than the threshold value [2, 3]. Downward relocation of the CSL within the context of the critical state soil mechanics can explain the continuing decrease in shear strength and the tendency towards the contraction observed in silty sands.