70 Liquefaction mechanisms and induced ground failure

Abstract

This chapter reviews mechanisms controlling liquefaction, subsequent soil deformation, and methods of analysis commonly applied in engineering practice. Field and laboratory tests indicate that liquefaction and subsequent ground deformation comprise complex phenomena that are difficult to model either physically or analytically. Thus, empirical procedures have become the standard of practice for evaluation of liquefaction resistance, prediction of ground deformation, and design of remedial measures. The formal definition of soil liquefaction is “the transformation of a granular soil from a solid state to liquefied state as a consequence of increased pore water pressure and reduced effective stress.” With the soil in a liquefied and softened condition, ground deformations occur readily in response to static or dynamic loading. The amount of deformation is a function of loading conditions, amplitudes and frequencies of seismic waves, the thickness and extent of the liquefied layer, the relative density and permeability of the liquefied sediment, and the permeability of surrounding sediment layers. Only when liquefaction leads to large ground deformation or ground failure is it hazardous to constructed works. Liquefaction may lead to any one of several forms of ground failure, depending on surface loads, site geometry, and the depth, thickness, and extent of the liquefied layer. Ground failures are divided into two general categories depending on whether induced ground movements are primarily lateral or vertical. Damage occurs when liquefaction leads to intolerable ground displacements or ground failure. Failure types include flow failure, inertially induced embankment deformation, lateral spread, loss of bearing strength, and ground settlement.