The contact properties of naturally occurring geologic materials: contact law development

This effort develops contact laws and presents material-specific parameters for those laws for several granular geologic and two manufactured materials. The normal contact law includes a Hertzian elastic term and a linear delayed elastic (anelastic) term which accounts for hysteresis. The shear contact law contains terms for elastic and anelastic deformation and an additional nonlinear term for inelastic (permanent) deformation that acts above an experimentally determined threshold ratio of shear to normal force at the contact. The contact laws have been formulated for arbitrary, quasistatic loading paths and are shown to capture the behavior observed in grain-to-grain contact experiments under monotonic and cyclic loading. The findings are based on the results of previously published normal and shear contact experiments on four naturally occurring quartz sands, magnesite (limestone), crushed and ball-milled gneiss, ooids (precipitated calcium carbonate spheroids), glass beads and a synthetic (Delrin). A companion paper presents the implementation of these laws in a discrete element simulation of a standard geotechnical triaxial cell and validates the simulations with physical triaxial experiments.