SCEC Award Number 20106 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Impact of Contact and Interface Modeling on Precarious Rock Fragilities - Phase 2: Experimental Verification
Investigator(s)
Name Organization
Christine Wittich University of Nebraska, Lincoln
Other Participants 1 Ph.D. Student (TBD)
SCEC Priorities 5b, 5c, 4b SCEC Groups Geology, SAFS, EFP
Report Due Date 03/15/2021 Date Report Submitted 03/08/2024
Project Abstract
 The primary aim was to assess how variations in the interface geometry of PBRs influence probabilistic overturning predictions, essential for understanding seismic hazards. he research team employed a hybrid methodology, integrating experimental shake table tests with advanced three-dimensional numerical modeling. Two granite rock specimens, one unchiseled and the other chiseled, underwent 1164 earthquake simulations on a shake table. High-resolution LiDAR systems provided precise geometric data, crucial for both creating the numerical models and monitoring the evolution of the rock interfaces.Numerical analysis utilized the Distinct Element Method (DEM) to simulate complex failure modes in PBRs, including rocking, sliding, and overturning. These simulations, aligned with the shake table tests, revealed the impact of varying normal stiffness on the seismic stability of PBRs, with chiseled specimens showing increased stability. Probabilistic analysis, using vector-valued fragility and logistic regression, indicated that increased normal stiffness correlated with more stable models and lower overturning probability. The study also considered other contact parameters like shear stiffness and friction angle, further underscoring the importance of interface geometry in PBR seismic response predictions.
Intellectual Merit The proposed project closely aligns with the objectives and priorities of the Earthquake Geology disciplinary committee, which aims in part to foster research in outstanding seismic hazard issues and in the earthquake history of southern California. To this end, the analysis of precarious rocks and fragile geologic features has been identified as a particular strategy to evaluate ground motion hazard and inform seismic hazard methodologies. While precarious rocks are recognized as a means to evaluate hazard, it is also understood that existing analysis techniques carry potentially significant uncertainty and the development of analysis techniques is a noted research priority of this particular disciplinary committee. This project directly addresses this research priority through the analysis and quantification of epistemic uncertainty associated with interface geometry of precarious rocks and the impact that this may have on subsequent fragility analyses.
Broader Impacts This project directly contributed to the dissertation of 1 PhD student. In addition, 3 undergraduate students directly participated in the shake table testing, including 1 from an underrepresented group. Shake table testing was also used during outreach events visiting UNL's College of Engineering, where the events were directed to encourage participation in STEM for young women and other underrepresented groups.
Exemplary Figure Figure 5 Raw shake table results a) SP1 b) SP2 c) Changes in SP2 with respect to SP1