Liquefaction of Thawed Layers in Frozen Soil

A dynamic effective stress method is presented for assessing the liquefaction potential of thawed layers of saturated cohesionless soils sealed between frozen surface layers and permafrost. Such layers are common in Arctic regions. Analysis indicates that the liquefaction potential is increased by the presence of a frozen surface layer. The pore-water pressures created by dynamic stress gradients are redistributed upwards to regions of lower effective stresses, and they cannot dissipate because drainage is sealed off, thus leading to increased liquefaction potential. Within limits yet to be established, the coarser the soil, the greater the risk of liquefaction at low densities as upward redistribution of pore-water pressures is facilitated by increased permeability. Field data on liquefaction from the Alaska earthquake of 1964 are examined, and they appear to support the conclusions.