No guidelines are available for evaluating the liquefaction potential of silt-clay mixtures during an earthquake, based on their simple property i.e. density, void ratio, plasticity index, and standard penetration values. The liquefaction behavior of these soils is not properly understood at present (2000) and is often confused with that of sand-silt mixtures. Pore water pressure generation mechanism of silt and silt-clay mixtures is discussed based on the published information. Through
statistical analysis, an approximate correlation between cyclic stress ratio (CSR) for initial liquefaction and plasticity index (PI), initial void ratio (e0) and number of cycles (N) has been established. It is shown that an increase in plasticity index lowers the cyclic stress ratio for liquefaction in low plasticity range. There appears to be a critical value of plasticity index at which the resistance to liquefaction of silty soil is at a minimum. The liquefaction resistance of silt-clay mixtures increases with the increase of plasticity index beyond this critical point. A physical explanation for this behavior is presented.