Mechanisms to explain soil liquefaction triggering, development, and persistence during an earthquake

Mechanisms have been proposed to explain the triggering, development, and persistence of soil liquefaction. The mechanism explaining the horizontal failure plane (triggering) and its depth below the phreatic surface is governed by the flux properties and effective stress at that plane. At the failure plane, the pore water pressure was higher than the effective stress, and the volume change was the highest. The pore water pressure is a function of the soil profile features (particularly the phreatic zone width) and bedrock motion (horizontal acceleration). The volume change at the failure plane is a function of the intrinsic permeability of the soil and bedrock displacement. The failure plane was predicted to occur during the oscillation with the highest amplitude, disregarding further bedrock motion, which was consistent with low seismic energy densities. Two mechanisms were proposed to explain the persistence of soil liquefaction. The first is the existence of low-permeability layers in the depth range in which the failure planes are predicted to occur. The other allows for the persistence and development of soil liquefaction; it is consistent with homogeneous soils and requires water inflow from bedrock water springs. The latter explains many of the features of soil liquefaction observed during earthquakes, namely, surficial effects, “instant” liquefaction, and the occurrence of short- and long-term changes in the level of the phreatic surfaces. This model (hypothesis), the relationship between the flux characteristics and loss of soil shear strength, provides self-consistent constraints on the depth below the phreatic surfaces where the failure planes are observed (expected to occur). It requires further experimental and observational evidence. Similar reasoning can be used to explain other saturated soil phenomena.