Evaluation of static liquefaction potential of silty sand slopes

The mechanism of instability in granular soils is explained and its requirement as a forerunner to the liquefaction of level or sloping ground is described. Case histories support the observation that it is silty sands that liquefy under static and a majority of earthquake-induced conditions. Recent experiments show that clean sands do not behave similarly to silty sands. Tests on loose, silty sand indicate a reverse behavior with respect to confining pressure and this violates the basic assumption that loose, silty sands behave similarly to loose, clean sands. Strong correlations between fines content, compressibility, and liquefaction potential are often found for these soils. A procedure for the analysis and evaluation of static liquefaction of slopes of fine sand and silt, such as submarine slopes, mine tailings, and spoil heaps, is presented. It involves determination of the region of instability in stress space in which potential liquefaction may be initiated and determination of the state of stress in the slope. A method of finding the state of stress is developed to predict the zone of potential liquefaction in simple slopes. Trigger mechanisms for initiation of instability followed by soil liquefaction are reviewed and mechanisms of soil strengthening are discussed.