Orange County Branch Newsletter
Interaction of MSE Abutments Under Seismic Loading
By Mr. Michael Givens, PhD, PE, PG, and Mr. Clint Isa, PE
The ASCE-Orange County Geo-Institute (GI) hosted a dinner on November 3, 2016 at the University of California, Irvine (UCI) University Club. The dinner, which was attended by nearly 40 people, consisted of a presentation about research on the seismic performance of mechanically stabilized earth (MSE) bridge abutments recently performed at the University of California, San Diego (UCSD). The presentation included information regarding UCSD’s geotechnical capabilities and a discussion about the motivation, background review, and experimental results for shake table testing and numerical modeling of a MSE abutment. The presentation was given by Mr. John McCartney, PhD, PE, who is an Associate Professor at UCSD; Prof. McCartney’s research student, Mr. Yewei Zheng, was also in attendance.
Prof. McCartney discussed research from a combined numerical and experimental study on the seismic performance of a geosynthetic reinforced soil integrated bridge system (GRS-IBS). Prof. McCartney explained that GRS bridge abutments are widely used throughout the US except in California because of concerns about their seismic performance. Such concerns are both geotechnical and structural in nature, and include backfill settlement, facing displacement, bridge deck and seat movements, impact forces at bridge/deck contact, superstructure/GRS abutment interaction, and conformability with the GRS philosophy of placing the bridge deck directly onto the reinforced soil mass. This research was geared to investigate these issues and was principally funded by California Department of Transportation (Caltrans) along with joint funding from other state transportation departments (Washington, Utah, and Michigan).
Prof. McCartney discussed the approach to their research, which consisted of exciting an instrumented ½ scale physical model on a shake table and comparing the physical models’ performances to the results of numerical modeling performed using FLAC2D and FLAC3D. Ultimately, the goal of the research was to investigate the dynamic performance of the GRS-IBS considering load and resistance factor design (LRFD). The shake table model was constructed to allow a GRS abutment to dynamically interact with a bridge deck supported on a concrete wall resting on a sliding platform that was separated from the shake table. Seven shaking test configurations were performed to investigate variable bridge loading, reinforcement spacing, and reinforcement material. The tests were heavily instrumented and the shake table applied 12 different motions, including earthquake records and sinusoidal pulsing. Current numerical modeling generally overpredicted the displacements and settlements, and improvements are being explored including constitutive relationships, compaction effects, and 3D effects from over-reinforcement due to transverse reinforcements.
Prof. McCartney went on to share some of the preliminary findings of the research. Because the research is still pending approval at this time, Prof. McCartney has asked that ASCE OC GI temporarily withhold discussion of those findings in this article. We encourage you to check back in a few months for an updated article and for a link to the presentation slides.
Update: A modified presentation has been provided below.
On behalf of the ASCE OC GI and our fellow board members, we would like to thank Prof. McCartney for his contributions to our event. Lastly, we offer our special thanks to our dinner sponsors: Hayward Baker Geotechnical Construction and Soil Retention Systems.