Protocol for the assessment of unsaturated soil properties in geotechnical engineering practice

The implementation of unsaturated soil mechanics into routine geotechnical engineering practice requires an evaluation of methodologies that may be used for the assessment of ''unsaturated soil property functions.'' Guidelines and recommendations need to be provided to practicing engineers. The guidelines need to take the form of ''engineering protocols'' that define acceptable standards for engineering practice. ''Engineering protocols'' for unsaturated soils engineering practice can be divided into ''preliminary design'' protocols and ''final design'' protocols. Both design levels involve the use of a variety of estimation procedures that have been proposed for various classes of geotechnical problems (e.g., unsaturated flow, shear strength, volume change, and distortion). The hierarchy in methodologies is based mainly on the costs and risks associated with a particular engineering project. In this paper, ''hierarchical levels'' are suggested that take into consideration the cost of various direct and indirect methodologies for the determination of unsaturated soil properties. Recommendations and suggestions are provided for methods for the determination and use of the soil-water characteristic curves (SWCC) and consequently, for the computation of unsaturated soil property functions (USPFs). Primary attention is given to estimation procedures best known to the authors and most appropriate for geotechnical engineering practice.