Fragility of precariously balanced rocks: shake table testing and numerical modeling for a sample granitic rock

M. Khalid Saifullah, & Christine Wittich

In Preparation June 2022, SCEC Contribution #13416

Precariously Balanced Rocks (PBRs) are a unique type of naturally occurring structures that are critical to test and constrain seismic hazard at long return periods. However, the information required to use PBRs in these hazard studies involves the discernment of the overturning potential of these rocks. In general, freestanding structures are known to show sensitivity to certain changes in ground motion, geometry, interface, material, and numerical parameters. Previous studies have shown that variations in numerical parameters, even on simple freestanding structures, can significantly alter the seismic response of these structures. Given the importance of uncertainty in seismic response for PBRs, for preliminary quantification of uncertainty brought by numerical parameters, a granite rock specimen (used as a representation of a PBR) is experimentally tested on a shake table under a large number of seismic excitations. The experimental overturning results are compared with the overturning results obtained from distinct element modeling of the same specimen with three different sets of numerical interface stiffness cases. It is concluded that the normal stiffness is a very important modeling parameter that accounts for a large amount of uncertainty in overturning predictions. Additional testing is necessary to fully quantify the uncertainty.

Citation
Saifullah, M., & Wittich, C. (2022, 06). Fragility of precariously balanced rocks: shake table testing and numerical modeling for a sample granitic rock. Poster Presentation at 12th National Conference on Earthquake Engineering.