Critical State of Sands Revisited: Fabric Effects

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Critical State Soil Mechanics (CSSM) is the paradigm of a framework for soil constitutive modeling. This paradigm will be constructively challenged from the perspective of one important missing factor: the effect of soil fabric, in particular sands, on the premises and conditions characterizing critical state. The hypothesis that the fabric, characterized by an appropriately defined fabric tensor representing the orientational distribution of particles, contact normals or void vectors, evolves towards a critical state value will be investigated by means of discrete granular mechanics (DEM) and continuum mechanics methods. The main objective will be the enhancement of the critical state conditions for stress and void ratios by one additional condition for critical state fabric, the incorporation of the results into a new fabric-enhanced CSSM constitutive framework, and the illustration by examples of fabric effects on constitutive and numerical modeling of Geomechanics boundary value problems. Understanding the sandy soil response when deformed and stressed, is of fundamental importance for the safe design and analysis of geotechnical structures. The existing famework of the most predominant theory, Critical State Soil Mechanics, is in need of an enhancement to account for particular aspects related to the way the soil particles are oriented during their natural deposition process. The project will adress these issues by means of discrete particles modeling simulations and ensuing continuum mechanics methodologies. The successful outcome will drastically change the way CSSM theory is taught at Universities and applied in geotechnical practice, a field of increasing social impact in regards to hazard mitigations related to earthquakes and landslides. It will also offer an engineering perspective to the neighboring fields of granular physics and material sciences, where a continuum engineering approach to fabric effects can be very useful. Such findings will be integrated into an educational program leading to seminar presentations of the simplest aspects to young students and the development of graduate courses. The results of the proposed study will be disseminated through workshops, publications in archival journals and presentations at conferences.