Effect of fines content on liquefaction potential of sands

One of the most dramatic causes of damage to infrastructure during earthquakes is liquefaction of saturated sandy soils. While liquefaction has been reported in numerous earthquakes (Seed, 1968), the phenomenon has been more dramatically illustrated in the Niigata, Japan Earthquake of 1964, the Alaska Earthquake the same year and recently in the Loma Prieta Earthquake of 1989. An understanding of this phenomenon is critical for mitigation against severe damages to buildings and various superstructures during earthquakes.; The purpose of this dissertation is to investigate the effect of fines on liquefaction behavior of sand by using stress and strain controlled consolidated undrained cyclic triaxial tests. It is also aimed to provide a framework for understanding the stress-strain behavior silty sands and offer guidelines for future research. The second purpose of the dissertation is to compare the laboratory test data with a theory based on the density of dissipated energy during cyclic loading. The theory originally is used for pure sand. Here, it is modified to give closer approximations for the experimental findings on silty sand. The model was successfully predicted the test results.; The resistance of soils with addition of 10% low plasticity and non-plastic fines compared to clean sand has small significance on the pore pressure generation of sand. Though adding 10% low plasticity fines slightly increases the resistance to liquefaction while addition of 10% non-plastic fines decrease the liquefaction potential. As non-plastic fines content increases up to a level of 30%, the liquefaction resistance decreases. There is a level of cyclic shear strain below which, there is little pore water pressure generation in saturated silty soils. This threshold strain level is similar to those observed in sands and is in the order of 0.01 percent.; It is anticipated that the outcome of this research will help engineers better understand the behavior of silty soils under seismic conditions and enable them to come up with a much comprehensive guideline or design against liquefaction of silty soils.