Evolution of Contact Shear Resistance and Arching in Silica Sand

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

The time-dependent behavior of granular geomaterials is among the least understood of their characteristics, and arching in granular materials is an elusive phenomenon without the definitive mathematical framework needed for engineering analyses. This research addresses time-dependent evolution of contacts between silica sand grains, with its consequences on strength, stiffness, and arching formation in sand. This study seeks to discover microscopic processes which govern the behavior of soils. A link between evolution of inter-grain contacts and arching in granular geomaterials is sought, with a goal of a more informed use of arching in engineering analyses. The twofold purpose of the study is in promoting progress in science, and in benefits to society stemming from application of the research results in the development of national infrastructure. Behavior of soils is typically described by phenomenological models that predict their response to loads and load duration on the engineering scale. These models, however, do not explain the physical cause of the behavior they describe. In order to exercise any influence over the material behavior, the origin of the behavior needs to be discovered. This research addresses the fundamental question of why silica sand contacts exhibit time-dependent behavior that leads to time-dependent evolution of contact shear resistance and stiffness. A new generation of grain-scale testing apparatus will be constructed to test grain contacts subjected to complex loads. Testing of contacts will give rise to a mathematical description of contact behavior, which, subsequently, will be upscaled to the networks of grain contacts, and to the engineering scale behavior. The influence of the evolution process of material properties that originates at inter-grain contacts on formation of internal arches in soil masses will be studied. Both the distinct element approach and finite element analysis will be carried out to gain insight into the elusive phenomenon of arching in granular materials. The outcomes of the research will be illustrated with engineering applications. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.