Fabric structure of granular materials in jammed and flow states

Sponsor: Start-up fund provided by CUBoulder

Role: PI

Objectives

This research theme focuses on decoding the interrelation between fabric, stress-strain, and critical state of granular materials. Thanks to the extensive research on soil fabric in recent years, it is now understood that fabric is the core vehicle linking the stress and strain of granular soils. Modelling wise, however, majority of the elastoplastic soil models which were developed without or with limited reference to soil’s internal structure. We hypothesized the existence of a critical fabric surface (CFS) that attracts fabric state of granular materials upon shearing. This condition can be reduced to the classical stress-based critical state condition but is more general for its purely kinematic nature (i.e. soil fabric can be observed any time while stress is not directly observable). We then developed the critical fabric theory (CFT) revolving around the concept of CFS, aiming to unify the typical sand behaviors such as static and cyclic liquefaction, ratcheting, dilatancy, critical state and the corresponding fabric evolution trend under a variety of loading paths. We hope the concept of CFS can be also extended to understand the physics of granular materials even at unjammed and shear jammed states, which is beyond the classical soil mechanics applications.

DEM data shows the existence of a unique critical fabric surface for granular materials regardless of the initial stress state, packing, and shear mode.

Another trust of research under this umbrella is to study the evolution of soil internal structure during internal erosion (suffusion). Suffusion removes fine particles and encourages the formation of flow channels that may initiate piping failure, the micromechanism of which is still poorly understood. We use the coupled CFD-DEM simulation to reproduce suffusion under controlled boundary conditions. We then observe suffusion-induced change of soil fabric and void redistribution and quantify their mechanical consequences to help improve dam safeties.

CFD-DEM coupled simulation of suffusion in gap-graded granular soils.

Collaborators

Zheng Hu, Ph.D., Sun Yat-sen University

Zhongxuan Yang, Ph.D., Zhejiang University

Publications

Wen, Y., Zhang, Y. (2022). Fabric-void ratio relation for granular materials. Acta Geotechnica, published online. DOI: 10.1007/s11440-022-01507-7.

Wen, Y., Zhang, Y. (2021) Evidence of a Unique Critical Fabric Surface for Granular Soils. Géotechnique, in press.

Hu, Z., Yang, Z.X., Guo, N., Zhang, Y. (2022). Multiscale modeling of seepage-induced suffusion and slope failure using a coupled FEM–DEM approach, Computer Methods in Applied Mechanics and Engineering, in press. DOI: 10.1016/j.cma.2022.115177

Hu, Z., Yang, Z.X., Zhang, Y. (2020) CFD-DEM modeling of suffusion effect on undrained behavior of internally unstable soils. Computers and Geotechnics, Accepted, DOI: 10.1016/j.compgeo.2020.103692.

Hu, Z., Zhang, Y., Yang, Z.X. (2019) Suffusion-induced evolution of mechanical and microstructural properties of gap-graded soils using CFD-DEM. Journal of Geotechnical and Geoenvironmental Engineering 146(5), 04020024, DOI: 10.1061/(ASCE)GT.1943-5606.0002245.

Zhang, Y., Zhou, X., Wen, Y. (2019) A constitutive theory for sand based on the concept of critical fabric surface. Journal of Engineering Mechanics 146(4), 04020019, DOI: 10.1061/(ASCE)EM.1943-7889.0001741.

Hu, Z., Zhang, Y., Yang, Z.X., (2019) Suffusion-induced deformation and microstructural change of granular soils: a coupled CFD-DEM study. Acta Geotechnica 14(3), 795-814.

Hu, Z., Yang, Z.X., Zhang, Y. (2018). Suffusion-induced deformation and microstructural change of granular soils: a CFD-DEM coupling perspective. In IS-Atlanta 2018, Geomechanics from Micro to Macro in Research and Practice, Atlanta, GA.