Ph.D. Thesis Defense Announcement

MODELLING BASED DESIGN AND OPTIMIZATION OF SPIDER-WEB INSPIRED GEOGRIDS IN COMPOSITE GEOMATERIAL SYSTEMS

By Candas Oner

Advisor:

Dr. J. David Frost

Committee Members: Dr. Fernando Patino-Ramirez (CEE), Dr. Rodrigo Borela Valente (SCI), Dr. Michael E. Helms (ME), Dr. Mark H. Wayne (Tensar), Dr. Jason T. DeJong (CEE/UC Davis)

Date and Time: May 28, 2025. 2:00pm

Location: SEB 122

Microsoft Teams Meeting ID: 273 217 231 733; Passcode: pe6Vd7Yj

Complete announcement, with abstract, is attached.

ABSTRACT
Geogrid reinforcement is typically used to stabilize the soil, both by interlocking soil
particles and by providing lateral restraint. These planar geogrid structures are used
in numerous different geotechnical engineering applications, such as pavements,
retaining walls, foundations, and encapsulation of stone columns. Spider-Web
Inspired Geogrids are a concept that attempts to enhance and optimize the design
of polymeric geogrid structures for ground reinforcement.
In 2019, researchers at Georgia Tech began exploring the opportunities for new
geometric configurations of geogrids. Based on inspiration from spider webs, these
studies identified, early on, the characteristics of spider webs that could be
beneficial to their performance, including different aperture sizes and continuous
Georgia Institute of Technology
School of Civil and Environmental Engineering
Atlanta, Georgia 30332-0355 U.S.A.
Phone: 404.894.9044
A Unit of the University System of Georgia • An Equal Education and Employment Opportunity Institution
radial elements, amongst others. The resulting geogrid structures are referred to by
the name SpiderAx throughout this study.
The three main features of SpiderAx geogrids are a stiff/condensed center region, a
large number of radial members, and the unique shapes created by the intersection
of those radial members with concentric chords. This added complexity to the
geogrid design from bio-inspiration comes with the question of how to integrate the
resulting ‘unit-cell’ spider-web inspired structures into a larger structure. This study
uses structural optimization concepts to optimize and enable the integration of
those initial unit-cell structures. Different numerical methods are employed to test
the effectiveness of these optimized structures. To test its structural properties,
such as its behavior under compressive and shear loading, the Finite Element
Method is used. A coupled approach between the Finite Difference Method and the
Discrete Element Method is utilized to evaluate the stabilization effect of geogrids
on natural aggregate systems under varying boundary conditions.
According to the results of the analyses performed with the Finite Element Method,
the total normalized strain energy stored in SpiderAx is less than for other geogrid
configurations, which is related to the stiffer geogrid behavior. This baseline case is
then elaborated with different parametric analyses, including different node and rib
dimensions, eccentric loading conditions for the plate load testing, and shearing
orientation and the initial surcharge pressure for interface shear testing. In optimal
forms, it is demonstrated that SpiderAx configurations can lead to both economic
and mechanical advantages.
Later in the thesis, the engineering performance of the geogrid is investigated with
the reverse approach, meaning that the influence of the geogrid on the stabilization
of the soil is analyzed. The influence of different parameters such as geogrid
stiffness, boundary conditions, loading plate diameter, geogrid thickness, clump
size, and clump aspect ratio are studied. It is shown that while the increase in the
geogrid thickness and geogrid stiffness lead to better performance in terms of
surface rutting, increase in the loading plate diameter hinders the ability of the
geogrid to stabilize the soil in the simulations. It is also illustrated that in order to
investigate the clump size and aspect ratio, a combined analysis with the geogrid
aperture should be performed, because it is found that the compatibility between
those can influence the benefits of using geogrids.