Ph.D. Thesis Defense Announcement

Experimental and Computational Evaluation of Geomaterial Interactions in Pavements

by

Sangy Hanumasagar

Advisor:

Dr. J. David Frost (CEE)

Committee Members:

Dr. Susan E. Burns (CEE), Dr. Arun M. Gokhale (MSE), Dr. Mark H. Wayne (Tensar International Corporation), Dr. Sung-Hee Kim (University of Georgia)

Date & Time: Thursday, October 10, at 8am

Location: Sustainable Education Building (SEB), Room 112

Abstract:

Improving the design and performance of pavement systems has been a topic of extensive research in the past few decades, with the two-fold objective of reducing construction and maintenance costs of roads while extending their duration of serviceability. While geosynthetics have been identified as viable means to stabilize and/or reinforce pavements at lower life-cycle costs and achieve improved performance of the resulting systems, their widespread adoption has been slow owing to several challenges. Some of these challenges arise from a lack of technical understanding about complex mechanisms such as interaction between aggregates and geosynthetics, while some others arise from inherent difficulties associated with pavement testing such as experimental design, specimen size and testing costs.
 
This research study aimed to address these specific challenges by developing a new bench-scale pavement simulation system to facilitate rapid standardized testing by employing downscaled specimens while still preserving mechanisms associated with full-scale pavements. The system was then used to conduct series of rutting tests to  assess the influence of various parameters like subgrade stiffness, aggregate morphology, geosynthetic type, geometry, placement location in the aggregate layer on pavement performance. The resulting time-series data of surface displacements and subgrade stresses yielded valuable insights into the internal mechanisms active within the specimen, particularly relating to the interlocking behavior between aggregates and geogrids. Further, a back-calculation procedure for the estimation of the approximate composite modulus of the stabilized pavement is presented, which could enhance current Mechanistic-Empirical design workflows for geosynthetic-stabilized pavements. Next, in an attempt to better understand the interlocking mechanics associated with aggregate-geogrid interaction, rutting experiments were conducted using aggregates of different morphologies and geogrids of different stiffnesses and opening sizes. This allowed for a detailed parametric assessment and demonstrated the importance of choosing the right aggregate-geogrid combination to maximize interlocking and therefore, performance. Finally, these insights from experiments were supplemented with a suite of Discrete Element Modelling (DEM) simulations to visualize interaction mechanisms at a particle-scale. Some compelling results showing the influence of geogrids towards limiting lateral spreading of particles across the aggregate layer are presented. 
In summary, this study helps gain a deep understanding of geosynthetic benefits over soft subgrades and geogrid interlocking mechanisms with different types of aggregates in various design configurations.