Ph.D. Thesis Defense Announcement

MULTISCALE ASSESSMENT OF FABRIC IN GRANULAR SOILS

By Srinivas Vivek Bokkisa

Advisor:

Dr. Jorge Macedo

Committee Members:  Dr. David Frost (CEE/GT), Dr. Sheng Dai (CEE/GT), Dr. Pedro Arduino (CEE/Univ. of Washington), Dr. Alba Yerro-Colom (CEE/Virginia Tech), Dr. Alexandros Petalas (Offshore Geotechnics/Durham University)

Date and Time:  April, 21, 2026.  11 AM (ET)

Location: SEB122 or https://gatech.zoom.us/j/92868470813

ABSTRACT
Soil fabric, the internal organization of particles, contacts, and voids, is a fundamental
variable governing the mechanical behavior of granular soils. Within the framework of
Anisotropic Critical State Theory (ACST), this thesis investigates the role of soil fabric
across constitutive and macro scales, while also examining the microstructural basis of its
constitutive representation. At the constitutive scale, the results show that the onset of
instability is a directional and fabric-sensitive phenomenon governed by loading path, fabric
anisotropy, and state. Under generalized loading, these interactions give rise to fabricdependent
instability surfaces that distinguish stable from unstable states. The analyses
further show that the influence of initial anisotropic consolidation on instability depends on
the coupled effects of material compressibility, stress path, and fabric evolution. To support
the reliable engineering application of ACST-based modeling, robust stress-integration
strategies are also developed and evaluated. At the macro scale, Material Point Method
simulations show that cone penetration response is strongly fabric-sensitive, with different
initial fabric orientations producing markedly different cone resistances even in soils with similar initial state. At the microstructural scale, X-ray micro-computed tomography and
image-based characterization of a clean sand prepared by different deposition methods show
that deposition history leaves a clear and measurable signature on inherent fabric, even at
similar global void ratio. The results further show that the measured fabric depends on both
preparation method and the microstructural descriptor used to characterize it. Although the
magnitude of anisotropy varies among descriptors, the dominant initial fabric direction
remains predominantly horizontal, providing an experimental basis for interpreting initial
fabric tensors in ACST-based models. Overall, the thesis identifies soil fabric as a key
multiscale variable governing granular soil behavior and provides new insights for its
interpretation and modeling in geotechnical engineering.