The understanding of the complex behavior of geological materials such as sand, clays, rocks, soils and construction materials has special interest for engineering applications and geo-hazard modelling. A gap has been created between theoreticians and practitioners of the mechanics of these materials. The first ones have been developing sophisticated continuous models to describe the complex behavior of these materials. These models include a large number of material parameters, most of them lack of physical meaning. Practitioners claim that the mechanical properties should be given in terms of the granulometrical properties, such as grain size distribution, angularity of the grains, contact parameters and properties of the materials filling the void spaces. Based on a simple multiscale analysis and some heuristic approximations, we derive incremental relations for geological materials in terms of those granulometric properties. We discuss on the micro-mechanical modeling by coupling the solid and liquid phases of the geological materials, the meso-scale modeling by using Discrete Element Modelling to find evolution equations of the "internal variables" of the constitutive model, and the engineering/geological scale by using conservation equations on continuum variables of the materials.