Li Xu is a professor, doctoral supervisor, director of the geotechnical laboratory, and director of the Subgrade Engineering Research Institute of Beijing Jiaotong University. He mainly engaged in traffic geotechnical engineering, special soil mechanics, numerical calculation of geotechnical engineering, and risk assessment. He received the first "Huang Wenxi - Chen Zongji" Geo-mechanics Youth Award and the first prize in natural science from the Ministry of Education. Dr. Li is an author of over 70 international journal papers.Hongfen Zhao is an associate professor of the School of Civil Engineering at Sun Yat-Sen University. Her research interests are focused on assessing the impact of environmental loads on the behavior of geomaterials across a wide range of scales and on the performance of geotechnical structures. She has published over 20 papers on those topics. Limin Zhang is Chair Professor and Head of the Department of Civil and Environmental Engineering at the Hong Kong University of Science and Technology, and Editor-in-Chief of Georisk. His research interests include geotechnical risk and reliability, embankment dams, landslides, multi-phase flows, and centrifuge modeling. He has published more than 300 international journal papers on the above topics.

• 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.

Li Xu is a professor, doctoral supervisor, director of the geotechnical laboratory, and director of the Subgrade Engineering Research Institute of Beijing Jiaotong University. He mainly engaged in traffic geotechnical engineering, special soil mechanics, numerical calculation of geotechnical engineering, and risk assessment. He received the first "Huang Wenxi - Chen Zongji" Geo-mechanics Youth Award and the first prize in natural science from the Ministry of Education. Dr. Li is an author of over 70 international journal papers.Hongfen Zhao is an associate professor of the School of Civil Engineering at Sun Yat-Sen University. Her research interests are focused on assessing the impact of environmental loads on the behavior of geomaterials across a wide range of scales and on the performance of geotechnical structures. She has published over 20 papers on those topics. Limin Zhang is Chair Professor and Head of the Department of Civil and Environmental Engineering at the Hong Kong University of Science and Technology, and Editor-in-Chief of Georisk. His research interests include geotechnical risk and reliability, embankment dams, landslides, multi-phase flows, and centrifuge modeling. He has published more than 300 international journal papers on the above topics.

• 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.