School of Civil and Environmental Engineering

Ph.D. Thesis Defense Announcement

Advancing Multi-scale Modeling of Penetrometer Insertion in Granular Materials

By

Jiaxing Su

Advisor:

Dr. J. David Frost (CEE)

Committee Members:

Dr. Susan Burns (CEE), Dr. Paul W. Mayne (CEE), Dr. Arun M. Gokhale (MSE), Dr. Gregory L. Hebeler (Golder Associates, Inc.)

Date & Time: Thursday, January 3, 2019, 10:00am

Location: Mason 3133

Complete announcement, with abstract, is attached

In the past three decades, studies on the mechanisms of interface shear in a variety of geotechnical problems have drawn significant attention. In response to the urgent need in understanding the shear behavior at particulate-continuum interfaces, several experimental and numerical studies on the effects of interface properties and loading conditions have been conducted at the Georgia Institute of Technology. To expand these studies, the current research focuses on developing numerical tools to study the response of interface systems under disturbed soil conditions. In particular, how does cone penetration affect the shear behavior at soil-penetrometer interface will be investigated in the current study, which is absent in the previous research on in-situ tests.

In this research, a novel testing technique for determining the angle of repose of sands was developed. A detailed study of the influence of particle properties on the angle of repose was conducted. The results were also used to calibrate a rolling resistance coefficient that not only quantifies the shape effects of the simulated particles but also reduces the computation complexity in the DEM simulations.

2D models of the MFA penetration test in calibration chambers subjected to both vertical and torsional loadings were developed to account for the disturbance of tip insertion on the interpretation of interface shear behavior at multiple scales. With proper adjustments, the shear zone was characterized and the disparity of microscale interface response under disturbed and in-situ soil conditions was evaluated.

Finally, a 3D DEM model with the ability to apply both axial and torsional shear loadings to the penetrometer-soil particle interfaces was built. The 3D model overcomes the drawbacks of the previous 2D models: 1) Each of these 2D models can only model the interface shearing under either axial or torsional loading condition; 2) The spatial interactions on particle level in real-time are lacking in the 2D models.