Granular materials are ubiquitous in nature and play a prominent role in countless technologies. The mechanical responses of multiphase granular material can vary significantly, when imposed to differential loading rates, depending on confinement, loading type and pore fluid properties. In this thesis, a versatile modelling platform is developed for delineating such behavioral fluctuations. The rate dependence of the solid and fluid phases is studied systematically, followed by their subsequent integration into a single modelling platform. Investigation of the compression behavior of the solid phase revealed that particle crushing plays a significant role in the mechanical response under both quasi-static and dynamic loading. A breakage model with adaptive fluidity is designed to simulate the rate-dependent compression of crushable granular solids. Specifically, the relationship between dynamic grain scale processes and bulk-scale dissipation is modeled by tracking the evolution of a state variable linked to micro-scale entropy fluctuations. Next, the rate-dependent variation of shear dilatancy behavior is explored. To circumvent the complications of implementing entropy-based constitutive models for mixed loading modes, a constitutive law is strategized by the direct incorporation of local kinetic energy increments within the energy equation. The strategy is implemented within the existing breakage model augmented with shear dilation properties. Apart from the solid phase, fluid drainage and compressibility also affect the mechanical response of multi-phase geomaterials subjected to high rates of deformation. While numerical simulations are powerful tools to examine partial drainage, their use in conjunction with advanced constitutive laws is computationally expensive. Therefore, a lumped modelling approach is proposed to address partially drained loading in a simplified, yet computationally efficient, way. The proposed approach consists of an inelastic constitutive law coupled with a spatially condensed fluid mass balance equation. Following this, the effect of the fluid compressibility is incorporated, to examine the emergence of coupled flow-deformation feedbacks even in dry sand beds subjected to rapid dynamic forcing. Finally, all the rate-dependence sources investigated in this thesis are incorporated into an uniform modelling platform to evaluate their individual roles and combined influence. The integrated model could capture the responses of sands for varying combinations of packing density, loading rate, degree of saturation, and hydraulic conductivity. The responses are compared, with emphasis to the difference between water-saturated (wet) and air-saturated (dry) systems characterized by the same packing density and confinement. Wet sands exhibited non-negligible strength changes at much lower strain rates in contrast to dry sands (air saturated). Increasing the strain rates further, the solid phase displays viscous behavior at vacuum conditions (i.e., without any pore fluid contribution). Thus, the traditional assumption of rate independence of granular media is only applicable up to a threshold loading rate, after which rate-dependent deviations must be considered to avoid inaccurate strength predictions.

Creator

• Ray, Ritaja

DOI

• https://doi.org/10.21985/n2-5g9b-w124

Subject

• Geological engineering

Language

• en

Alternate Identifier

• http://dissertations.umi.com/northwestern:16281
• etdadmin_upload_930399

Keyword

• grain breakage
• pore compressibility
• High strain rate
• granular solid hydrodynamics
• partially saturated
• kinetic energy

Date created

• 2022-01-01

Resource type

• Dissertation

Rights statement

• In Copyright