Evolution of mesoscale bonded particle clusters in cemented granular material

Abstract

Research on the macroscopic behavior of cemented granular material in geomechanics is challenged by the lack of understanding in physical origin of experimental observations. Recent advances in microscopic investigations suggest the critical significance of contact behavior, such as bond breakage. The mesoscale link between contact behavior and macroscopic responses has not been well understood so far. Discrete element method (DEM) simulations were carried out in this study to investigate the formation and evolution of bonded particle clusters (i.e., particle groups connected by bonds), which is key mesoscale behavior of cemented granular material. DEM simulation results show that the highly non-uniform deformation within a sample (under imposed uniform strain) leads to spatially non-uniform events of inter-particle bond breakage, which allows the formation of particle clusters. Clusters of various sizes and angularities are interwoven with each other. Under mechanical loading, evolutions of cluster size, number and angularity exhibit three distinctive stages. In stage I (bond breakage ratio 0 < ω < 0.3), single particles at spatially random locations are detached from the overall bonded particle skeleton and float in voids of the skeleton. In stage II (0.3 < ω<0.7), a cluster family with a growing size diversity and continuous size distribution are observed. In stage III (0.7 < ω < 1.0), the maximum cluster size decreases quickly and all bonds are finally broken. Implications of the unique features of cluster evolution for constitutive model development are finally discussed.