Characterization and behavior of soils; actual objectives and requirements

The paper discusses several important and interesting issues of modern studies of soil behavior. After a series of milestones in the history of human geotechnical achievements and development of classical soil mechanics humanity nowadays is facing several challenges where other - mostly numerical - solutions are required. They are provided by various soil models. Some modern models are based on specific soil parameters, often not known in classical soil mechanics. Scientific understanding of their nature as well as new techniques and high-precision testing equipment for their experimental determination are necessary for the progress in such a research. Even water compressibility influences the accuracy of pore pressure measurements in advanced soil testing. The "front line" of modern studies in soil behavior is in nonlinear soil mechanics. Detailed consideration of the nature of this complex nonlinearity, especially in small-strain range, reveals its close relationship to microstructural and energy transformations of soils, development of instability state as a preparation to failure and finally, processes causing the observed effects are presented in the relationship with important threshold strain levels. Thematic collection: This article is part of the Leading to Innovative Engineering Geology Practices collection available at: https://www.lyellcollection.org/cc/Leading-to-Innovative-Engineering- Geology-Practices