Advancing multi-scale modeling of penetrometer insertion in granular materials

Penetrometer insertion;Interface shear;Angle of repose;Pseudo 3D structure reconstruction;DEM

Su, Jiaxing ; Frost, J. David Civil and Environmental Engineering Burns, Susan E. Mayne, Paul W. Gokhale, Arun M. Hebeler, Gregory L. ; Frost, J. David

University:Georgia Institute of Technology

Department:Civil and Environmental Engineering

关键词: Penetrometer insertion;    Interface shear;    Angle of repose;    Pseudo 3D structure reconstruction;    DEM;   

Others  :  https://smartech.gatech.edu/bitstream/1853/62629/1/SU-DISSERTATION-2019.pdf

美国|英语

来源: SMARTech Repository

【 摘 要 】

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 pre-sheared soil conditions. In particular, how does cone penetration affect the shear behavior at soil-penetrometer interface will be investigated in the current study. To comprehensively understand the interface behavior, the properties of the contacting components—soil and continuum surface—shall be extensively studied. Inherited from the novel design of the multi-friction attachment (MFA), the surface roughness of the continuum surface in the numerical simulations is controlled by varying the height of the textured elements on the surface. On the other hand, simulating exact particle shape is challenging and requires enormous computation power that is not easily accessible. Thus, a study on angle of repose was conducted and the results were used to calibrate a rolling resistance coefficient that not only quantifies the shape effects of the simulated particles but also reduces the computation complexity. Having these two components studied, three different DEM models were developed and studied. A 2D model of the MFA penetration chamber test was implemented to account for the disturbance of tip insertion on the interpretation of interface shear behavior at multiple scales. With proper adjustments, the shear zone during axial penetration was characterized and the disparity of microscale interfacial response under disturbed and in-situ soil conditions was evaluated. In addition, by substituting the MFA penetrometer with any other in-situ tools, the current model can serve as a tool to evaluate the insertion disturbance of other devices. After the insertion disturbance has been induced, the stress state and local void ratio near the penetrometer was extracted and used to initialize a 2D model of a textured sleeve during a torsional shear test. Facilitated by the technique of serial sectioning, interface shear behavior resulting from axial penetration disturbance and torsional shear loading was investigated at various penetration intervals. Together with the simulation of vertical penetration, spatial structures of the studied specimen in a pseudo 3D domain can be reconstructed. In this manner, with less computational cost than a real 3D model, detailed spatial interface shear behavior resulting from both axial and torsional shearing was obtained. Finally, a 3D DEM model with the ability to apply both axial and torsional shear loadings to the interface between continuum surface and soil particles was developed. 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; and 2) The spatial interactions on particle level in real-time are lacking in the 2D models. The results gained from the current 3D model were found to accurately describe many aspects of the observations of the laboratory tests, some of the microscale mechanisms at interfaces were obscured since the particle size has been enlarged by a factor of 5 in the simulation on account of the computational limitations.