Introduction -- Characterization of natural widely-graded colluvial soils -- Micro-porosity structures of widely-graded soils -- Techniques for measuring hydraulic properties for unsaturated soils -- Hydraulic properties for widely-graded soils -- A unified framework for unsaturated soils -- Mechanical behavior of widely-graded soils under low confining pressure -- Bimodal features for widely-graded soils -- Seepage analysis technique for unsaturated soils -- Assessing the stability of slopes composed by widely graded soil.