LIQUEFACTION CHARACTERISTICS OF GRAVELLY SANDS: STRAIN APPROACH

Liquefaction behavior of gravelly sands has been the focus of much research in recent years. In this study, various aspects of liquefaction characteristics of gravelly sands are addressed. An extensive experimental program was conducted to investigate the effects of gravel content, relative density, effective confining pressure, cyclic shear strain amplitude, and number of cycles. The study reveals the significance of strain level induced by the earthquake on liquefaction resistance of soil. Results have confirmed the existence of a constant characteristic threshold cyclic shear strain irrespective of relative density and confining pressure, ranging from 0.005% for gravel to 0.01% for sand. Some characteristics of the threshold strain and its important role in earthquake engineering are delineated. There is no danger of liquefaction if the cyclic strain induced by an earthquake is below the threshold level, even for the longest duration earthquakes. It is shown that cyclic strain is a more fundamental parameter than cyclic stress in controlling pore pressure buildup. Curves are established to predict pore pressure generation as a fiinction of cyclic shear strain and number of cycles irrespective of in situ relative density. It is shown that sand deposits with 20% gravel content have lower liquefaction resistance whereas resistance increases with further increase in gravel content. The use of strain approach is proposed to evaluate liquefaction potential of gravelly sand deposits.