Arda Sahin

Next Generation Liquefaction Project Database and Model Development in Support of Improved Liquefaction Hazard Assessments (2024 – Expected 2029)

U.S. Federal Highway Administration (FHWA)

Principal Investigators (PIs): Dr. Kristin J. Ulmer (SwRI), Prof. Jonathan P. Stewart (UCLA), Prof. Armin W. Stuedlein (OSU)

Co-PIs: Dr. John Stamatakos (SwRI), Prof. Scott J. Brandenberg (UCLA), Prof. T. Matthew Evans (OSU)

Participating Institutions: Southwest Research Institute; University of California, Los Angeles; Oregon State University; University of Washington (Prof. Steven L. Kramer)

• Developing probabilistic liquefaction susceptibility models from the NGL database as the first step of seismic ground failure hazard assessment
• Quantified hysteresis loop metrics to distinguish sand-like and clay-like behavior under cyclic loading
• Developed a web form (HTML, CSS, and JavaScript) to collect expert opinions on sand-like versus clay-like behavior for a subset of tests
• Related the expert opinions to the hysteresis loop metrics to build a framework for objectively assessing the full NGL database
• Developed a Bayesian inference framework to estimate soil behavior from hysteresis loop metrics while accounting for uncertainty in expert judgments
• Created an interactive Python/ipywidgets tool to access cyclic test data, compute hysteresis loop metrics, and visualize the results
• Evaluated all cyclic test results in the NGL database and created a protocol for identifying tests usable in liquefaction susceptibility assessment
• Relating liquefaction susceptibility to common index parameters, such as Atterberg limits, that are available in nearly all geotechnical projects
• Correlating liquefaction susceptibility with Cone Penetration Test (CPT) results to form a separate model, giving practicing engineers flexibility to use the most reliable data available for their project
• Co-authored two interim reports to FHWA summarizing the findings with the participating institutions

Evaluation of Simplified Procedures for Estimating Lateral Spreading (2025 – Expected 2027)

California Department of Transportation (Caltrans)

Principal Investigator (PI): Prof. Scott J. Brandenberg

• Developing lateral spreading models using the NGL database, considering geotechnical and geomorphological features

Next Generation Liquefaction Susceptibility Database and Modeling (2023 – 2025)

Pacific Earthquake Engineering Research (PEER) Center

Principal Investigator (PI): Prof. Jonathan P. Stewart

Co-PI: Prof. Scott J. Brandenberg

Participating Institutions: University of California, Los Angeles; Oregon State University (Prof. Armin W. Stuedlein, Dr. Amalesh Jana)

• Expanded the NGL database with cyclic laboratory, in situ, and index test data to address needs identified at the 2022 PEER Workshop held at Oregon State University (OSU)
• Traveled to Houston, TX, to gather key data used to develop a legacy liquefaction susceptibility model
• Coordinated with research groups at OSU, UC Berkeley, and UC Davis and with geotechnical engineering firms including Geosyntec and ENGEO
• Created and published DesignSafe datasets of site investigation and cyclic laboratory test results to make the data publicly available to the geotechnical engineering community
• Entered the gathered datasets into the NGL database so they can be easily queried using SQL
• Identified issues and missing input entries in the NGL database structure to guide future reorganization and redesign
• Created a logic tree framework for seismic ground failure hazard assessment and illustrated it with a case history from the 1999 Kocaeli earthquake

Effect of Fines on Liquefaction Triggering Analyses (2024 – 2025)

California Department of Transportation (Caltrans)

Principal Investigator (PI): Prof. Scott J. Brandenberg

• Developed a framework that separates the effects of fines content on penetration resistance and cyclic resistance
• Co-authored Caltrans Report CA25-4418

RAPID: Geotechnical Engineering and Geo-Sciences Response to the 6 February 2023 Türkiye Earthquake Sequence (2023 – 2025)

U.S. National Science Foundation (NSF)

Principal Investigator (PI): Prof. Jonathan P. Stewart

Participating Institutions: University of California, Los Angeles; California Polytechnic State University (Prof. Robb Eric S. Moss); Middle East Technical University (Prof. Kemal Önder Çetin); California State University, Fullerton (Prof. Sinan Akciz)

• Performed site investigations at locations where reconnaissance teams reported surface manifestations and at strong-motion stations, to estimate the effect of soil profiles on the amplification or de-amplification of ground motions
• Summarized the data and published it through DesignSafe to make it publicly available and advance the state of practice
• Compared site investigations at strong-motion stations with available models to identify their shortcomings, and added the data to the databases used to develop newer model versions
• Performed liquefaction assessments with the new site investigation data using legacy models and the NGL triggering model to test their applicability and performance
• Developed complete case histories, from reconnaissance through site investigation, for DesignSafe and the NGL database
• Mentored two undergraduate researchers (C&EE 199 directed research and summer research) developing new liquefaction case histories from the 2023 Türkiye earthquakes
• Co-authored a report to NSF summarizing the findings with the participating institutions

Reconnaissance after the February 6, 2023 Türkiye Earthquake Sequence (2023)

Geotechnical Extreme Events Reconnaissance (GEER) Association

Coordinators: Prof. Kemal Önder Çetin (METU), Prof. Jonathan D. Bray (UC Berkeley), Prof. J. David Frost (Georgia Tech), Prof. Robb Eric S. Moss (Cal Poly), Prof. Jonathan P. Stewart (UCLA)

Participating Institutions: Middle East Technical University; California Polytechnic State University; Georgia Institute of Technology; Southwest Research Institute; University of California, Berkeley; Portland State University; Ohio State University; University of California, Los Angeles

• Visited the affected region after the February 6, 2023 earthquakes, one of the most significant earthquake sequences of the past decade
• Joined field teams from Middle East Technical University and Gazi University, followed by GEER teams that visited the region in three phases from mid-February to the end of March
• Evaluated the performance of support systems, dams, bridges, lifelines, ports, and buildings affected by seismic ground failure, to inform future data collection, model testing, and model development
• Collected soil ejecta samples to classify the soils that liquefied during the earthquakes
• Measured excessive building settlements and lateral spreading displacements at port facilities, bridges, and dams
• Thoroughly investigated two port facilities, one with and one without surface manifestations, to develop a complete case history published in a journal paper
• Helped prepare reconnaissance reports for the Turkish research teams and GEER