Granular materials are complex systems that are receiving intense interest within the engineering, physics, and mathematics communities. These ubiquitous materials play a significant role in geosystems, mining, petroleum storage and extraction, ceramics engineering, and pharmaceutical science. The report reviews recent developments and new advances in experimental, computational, and modeling methods that extend understanding to a wide range of materials and phenomena: multi-phase systems with strong solid-fluid interactions; multi-field systems in which van der Waals and electrical fields gain dominance; and bonded granular systems for advanced pavements. Experimental advances include computed neutron and nanometer scale tomography, magnetic resonance imaging, refractive index matching, digital image correlation, and acoustic emission analysis. Complex systems and data mining tools are now being used to extracting meaningful information and patterns from data. The state of the art in continuum modeling has shifted to micromechanical or multi-scale approaches with developments being made from three perspectives: constitutive modeling enhanced by material fabric and fabric evolution; modeling discrete systems as equivalent continua; and computational multi-scale modeling. Advances in computational modeling and parallel computing are exploited to model the complexities of grains and contacts, and to study strongly coupled grain-fluid systems using computational fluid dynamics and particle-structure interactions using combined discrete and finite element methods. This report focuses on three broad advances in granular mechanics: the experimental imaging of granular materials (Part I); the transition between micro-, meso-, and continuum-scale modeling (Part II); and the modeling of multi-phase materials (Part III).