Mechanics of unsaturated soils : simple approaches for routine engineering practice

Abstract

A number of geotechnical structures involve the unsaturated upper portion of the soil profile, i.e. the zone above the phreatic surface where the pore-water pressure is negative and the degree of saturation is generally lower than unity. This zone is characterised by soil strength and stiffness higher than the saturated soil below the phreatic surface. In addition, its mechanical response is affected by the interaction with the atmosphere (rainfall and evapotranspiration). Engineers recognise more and more the importance of understanding and predicting the response of soils in the unsaturated portion of the soil profile. However, a gap still exists between research and engineering practice in unsaturated soil mechanics. This paper makes an attempt to serve fundamental concepts of unsaturated soil mechanics using a language as simple as possible. In particular, quantitative prediction tools are presented within the familiar framework of saturated soil mechanics. These include conventional ‘saturated/dry’ slope stability analysis and traditional 1-D consolidation analysis.