The geotechnical practice has long known and recognized that increases in pore water pressures associated with the development of the steady state seepage condition result in an associated decrease in effective stress in the soil. This decrease in effective stresses results in a reduction of the available effective strength of the soil. When artesian conditions develop in the field, the large pore water pressures trapped below a low permeability soil layer can lead to essentially zero effective strength. Under these conditions, the calculated slope stability factor of safety can be reduced to much less than half. Conditions that lead to artesian pore water pressures are commonly encountered in areas protected by levees, where a relatively thin, low permeability blanket overlays a permeable aquifer. This paper analyzes the influence of the pore water pressures in the calculated factor of safety for a wide range of conditions commonly encountered in the field.
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