There are other books on unsaturated soil mechanics, but this book is different. Unsaturated soil mechanics is only one aspect of a continuous range of soil mechanics studies that extends from the rheology of high water content soil slurries to the mechanics of soft soils, to stiff saturated soils, to unsaturated soils, and, at the far end of the range, to dry soils. In reality, the water content of all soils, that are not permanently submerged, varies seasonally. In most climatic zones, rainfall varies during the year and the depth of the water table varies sympathetically. In applying unsaturated soil mechanics in practice, it is therefore important to realise and allow for the probability that soil will, either seasonally or occasionally, pass from the unsaturated to the saturated state and even from unsaturation to dryness. This is the only book that looks specifically at this essential practical aspect. The theory of unsaturated soils is fully dealt with in all of its aspects, including its application to natural undisturbed soils and compacted soils. Application of the theory to soil-like materials such as mine waste and municipal solid waste is also covered. Application of the theory to practice is illustrated by a number of detailed case histories. Unsaturated soil mechanics principles can also successfully and usefully be applied in related fields such as the bulk storage of particulate materials, underground mine support, solution mining and concrete structures. Several case histories are given that illustrate these practical applications. The author has been professionally engaged in practical research and application of unsaturated soil mechanics for close to 60 years and with this book shares his wide experience with the reader.