Role of intergrain contacts, friction, and interactions on undrained response of granular mixes

A simple analysis of a two-sized particle system with large size disparity (e.g. sand and silt) is presented to highlight the relative roles of intergrain contacts and interactions between the finer and coarser grains on the undrained behavior, strength, and fragility of granular mixes. Intergranular (e(s)) and interfine (e(f)) void ratios are indices to qualitatively describe the behavior. The anticipated behavior is categorized into five subgroups. The anticipated stress-strain behavior, collapse potential, and steady state strength behavior for each group is further characterized in terms of the behavior of either the host coarser grain or the finer grain medium. Exceptions are also identified. The threshold finer grain contents and threshold intergranular void ratios delineating the transition boundaries between these subgroups are presented. This is experimentally evaluated. The results provide a mechanistic understanding of possible microscopic mechanisms that affect the liquefaction and post-liquefaction response of man made and natural deposits of silty sands, sandy silts and gravely soils. It can also be used to develop guidelines for interpretation of insitu and laboratory behavior of such soils and liquefaction mitigation design. Judicious caution is called for when this is extrapolated to well graded or layered soils.