The 1999 R.M. Hardy Lecture: The implementation of unsaturated soil mechanics into geotechnical engineering

The implementation of unsaturated soil mechanics into geotechnical engineer ing practice requires that there be a paradigm shift from classical soil me chanics methodology. The primary drawback to implementation has been the ex cessive costs required to experimentally measure unsaturated soil propertie s. The use of the soil-water characteristic curve has been shown to be the key to the implementation of unsaturated soil mechanics. Numerous technique s have been proposed and studied for the assessment of the soil-water chara cteristic curves. These techniques range from direct laboratory measurement to indirect estimation from grain-size curves and knowledge-based database systems. The soil-water characteristic curve can then be used for the esti mation of unsaturated soil property functions. Theoretically based techniqu es have been proposed for the estimation of soil property functions such as (i) coefficient of permeability, (ii) water storage modulus, and (iii) she ar strength. Gradually these estimations are producing acceptable procedure s for geotechnical engineering practices for unsaturated soils. The moistur e flux ground surface boundary condition is likewise becoming a part of the solution of most problems involving unsaturated soils. The implementation process for unsaturated soils will still require years of collaboration bet ween researchers and practicing geotechnical engineers.