Chapter 10 - Role of localized elevated pore pressures and strain localization mechanisms in slope stability problems

Abstract

This chapter discusses the major mechanisms for strain localization in geomaterials (i.e. soil and rock) and their possible implications for slope instability. In certain geological environments and slopes subjected to external forces, soil or rock does not completely fail, but deformation zones are created due to intense strain localization, resulting in morphological and geotechnical changes. Strain localization is a feature of elastoplastic materials where shear bands are formed as a result of inhomogeneous material deformation leading to permanent expressions of intense strain zones. Strain localization can be considered an instability in material constitutive behavior. Localized elevated pore pressures can drive the growth of a slip-failure surface in a manner similar to that observed during earthquake nucleation. The material within a deformation band is thought to strain harden as a result of the deforming mechanism. In porous geomaterials such as sandstone, deformation bands are the most common strain localization feature. The localized strain bands can occur in a shear or compaction form. Particle grains within deformation bands tend to be smaller, more compact, possess stronger preferred orientations, and have more elongate shapes than particles outside the band. To illustrate, the Oso Landslide that struck Snohomish County, Washington on Saturday, March 22, 2014, resulting in 43 fatalities, several injuries, and significant destruction of property is discussed. Observed sand boils and other signs of confined elevated water pressure reaching or exceeding total overburden pressure point to liquefaction at depth in Zones E and F during the Oso landslide. Strain localization likely occurred during Stage 2 of the failure, triggering the 300m length shearing of the failure surface.