Esteban Litvin, geotechnical engineer, Atkins
Landslides constitute a major threat to both lives and property worldwide, especially in tropical and subtropical areas such as South America, Africa and the Far East. These regions are characterised by periods of prolonged dry weather with periods of intense rainfall.
During dry periods negative pore-water pressures develop in the soils, which have a stabilising effect. When dry periods are followed by intense rainfall events, rainfall infiltration leads to an increase in positive pore-water pressures (a decrease in suctions) and a reduction in the shear strength on the potential failure surface – and slope failure is common.
To account for the influence of negative pore-water pressure on soil strength and hence on the factor of safety (FoS), Fredlund et al, 1978 developed a modified form of the Mohr-Coulomb failure criterion for unsaturated soils, which is as follows:
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