Geosyntec Staff to Present at ASCE Lifelines Conference
Geosyntec practitioners will deliver four presentations at the San Fernando Earthquake Conference – 50 Years of Lifeline Engineering (Lifelines 2021-2022). The conference will be a virtual event and Geosyntec is also a silver sponsor.
Practitioners delivering presentations are Chris Conkle, P.E., G.E.; Christopher Hunt, Ph.D., P.E., G.E., M.ASCE; and Yonas Zemuy, P.E. (California).
Chris Conkle is a Principal Geotechnical Engineer based in California with more than 17 years of experience focused on geotechnical investigation, evaluation, design, and quality assurance monitoring for a variety of dam, water resources, and infrastructure projects. Chris' dam safety experience includes serving as the project manager and technical lead for Geosyntec's Embankment Dam Stability Evaluation and On Call Dam Safety projects for Southern California Edison.
Christopher Hunt is a Senior Principal Geotechnical Engineer based in California with more than 20 years of experience focused on geotechnical and geoenvironmental projects. Chris's project portfolio includes foundation investigations and designs for pile-supported structures and shallow foundations.
Yonas Zemuy is a Senior Engineer with over 14 years of experience in landfill and geotechnical engineering. His expertise includes relevant experience with landfill fieldwork, laboratory testing programs, interpretation of in situ subsurface conditions drilling operations using the standard penetration and cone penetrometer test (CPT), soil classification, borrow-source evaluations, and laboratory testing results.
The ASCE Infrastructure Resilience Division (IRD), in partnership with The University of California, Los Angeles (UCLA), is hosting the San Fernando Earthquake Conference – 50 years of Lifeline Engineering (Lifelines 2021-2022), focusing on "Understanding, Improving & Operationalizing Hazard Resilience for Lifeline Systems." The February 9, 1971 San Fernando California Earthquake was a devastating yet seminal event which, for the first time, demonstrated the seismic threat to lifelines that fundamentally support our modern livelihoods. Knowledge gained from this event initiated the study of lifeline systems worldwide, including water, wastewater, electric power, gas and liquid fuels, communications, transportation, and solid waste management systems. The founding efforts of the ASCE Technical Council on Lifeline Earthquake Engineering, a predecessor unit to the current IRD, by international leaders like the late Charles Martin Duke from UCLA established lifeline systems into a mainstream discipline, now accepted as fundamental for community and regional resilience.
The 50th anniversary of the San Fernando Earthquake is an opportunity to reflect on the need to increase the resilience of our critical infrastructure systems to earthquakes and other hazards. The conference will provide a retrospective of where we are today and how we got here – and help define a global vision for where we are going to create resilient infrastructure systems within interdisciplinary and multihazard environments which support community and regional resilience. These encompass the conference goals.
Approach to Evaluation of Liquefaction and Lateral Spreading, and Application to Assessment of Potential Failure Modes for Seismic Risk Reduction at Wastewater Treatment Plants
Presenter: Christopher Hunt, Geosyntec
CoAuthors: Chris Conkle, Jacquelyn Allmond, Geosyntec; Jeff Fijalka, City of Manhattan Beach
Abstract: The Orange County Sanitation District's (OCSD) wastewater treatment plants located in Fountain Valley (Plant No. 1) and Huntington Beach (Plant No. 2), California were the subject of geotechnical evaluations as part of a program to identify seismic vulnerabilities and recommend mitigations for over 60 existing structures. Many of these facilities are exposed to liquefaction and lateral spreading hazards, and geotechnical approaches were developed to assess the potential for these hazards to cause structural damage and associated service disruptions. The study began in August 2017, and the final report was completed in July 2019 with a focus on identifying potential failure modes (PFMs) for each of these facilities along with associated recommended mitigation measures.
The geotechnical portion of the project began with a comprehensive review and databasing of available geotechnical information. The team then planned and executed a geotechnical investigation to supplement the historical data provided by the client. An analysis groundwater level was selected, and the geotechnical datasets were combined with ground shaking inputs to allow for systematic liquefaction triggering and associated settlement and lateral spread magnitude assessments. These assessments were used to develop profiles of liquefaction and lateral spread induced deformations associated with each structure. Structural analysis was then performed by others to assess the structural response to differential settlement and lateral spread patterns in parallel with the evaluation of the structures' response to ground shaking. Deformations were assessed and inputs to structural evaluations were developed for the wide range of structures at the two plants, including steel moment-resisting frame buildings, tilt-up concrete buildings, pump stations, cylindrical concrete digester tanks, rectangular concrete clarifiers, and concrete and steel surge towers. These structures were founded on a range of different foundation types, including deep foundations with some structures relying on tiedown anchors.
Proposed geotechnical mitigations were developed to address potential failure modes identified for the structures and were prioritized using an approach that categorized the risk associated with each potential failure mode, with consideration given to the likelihood of occurrence and the consequences of failure.
Seismic Resilience: Orange County Sanitation District is Planning For 2030 and Beyond Through a Risk-Based Evaluation of Their Process Facilities
Presenters: Chris Conkle, Geosyntec; Don Cutler, Orange County Sanitation District
CoAuthors: Chris Hunt, Geosyntec; Doug Lanning, Carollo Engineering, Inc.; Ahmed Nisar, InfraTerra, Inc.; Jeff Fijalka, City of Manhattan Beach
Seismic resiliency is a major concern for the stewards of our wastewater infrastructure throughout California. This particularly includes the Orange County Sanitation District (OCSD), who provides wastewater collection, treatment, and disposal services for approximately 2.6 million people in Southern California. OCSD has wastewater treatment plants located in Fountain Valley (Plant No. 1) and Huntington Beach (Plant No. 2). Because OCSD's facilities are exposed to local seismic hazards, including local faulting, liquefaction, and lateral spread, the potential for earthquake damage and associated service disruptions is a significant threat to their $11 billion infrastructure.
Many structures at OCSD's plants were constructed before the adoption of modern building codes. Older codes (prior to 2000 International Building Code [IBC] and subsequent 2001 California Building Code [CBC]) generally had lower estimates for seismic hazards and did not require mitigation of seismic-induced ground deformations. With this realization, OCSD has taken a proactive approach and conducted a study to evaluate structures at both treatment plants for potential seismic hazards, including identification of mitigation strategies to improve operational resiliency following a large earthquake. Based on the findings from this study, a plan was developed to identify and prioritize mitigation projects using a risk-based methodology. This is the foundation for integrating seismic resilience into OCSD's overall capital improvements program.
OCSD's seismic resiliency study evaluated 63 facilities in total, covering a wide range of structures, including buildings, pump stations, clarifiers, and digesters. The study began in August 2017, and the final report was completed in July 2019. The focus of the study was to identify potential failure modes (PFMs) for each of these facilities, including risks from strong ground shaking, liquefaction induced differential settlement, and lateral spread. Based on the PFMs, mitigative measures were identified to address deficiencies in the structures. Because of the number of facilities that were evaluated, it was necessary to develop a unique approach that identified exemplar structures that represented common design and construction techniques that would demonstrate similar performance during a seismic event. The exemplar structures were evaluated using a 3D finite element analysis to model performance. The results of this analysis were extrapolated to other structures with similar characteristics to identify vulnerabilities.
It was also necessary to develop an approach to categorize the risk associated with the potential failure modes, including an evaluation of the likelihood of occurrence and the consequence of failure. A risk-based prioritization was utilized to integrate seismic resilience into OCSD's on-going planning for their $5 billion capital improvement program (CIP) over the next 20 years. This work expands on the unique methodology used by OCSD to evaluate their facilities and how this process was integrated into their capital improvements program.
Considerations for the Application of Risk Informed Decision Making on Dam Safety Projects
Presenter: Chris Conkle, Geosyntec
CoAuthors: Matt Muto, Patrick Le, Southern California Edison
Abstract: Various states and other agencies are developing risk-informed decision making (RIDM) guidelines for dams. FERC is also in the process of integrating RIDM into its dam safety program and has promulgated interim RIDM Guidelines. The RIDM process typically includes an assessment of the likelihood of loading, the dam's fragility under loading, and the consequences of uncontrolled release to estimate life safety risk. This risk estimate can be used to decide if dam safety improvements are warranted. As part of the FERC rollout, several dam owners are conducting pilot projects as trials of the process that will provide valuable input to others who will use RIDM in the future. One of these projects is Southern California Edison's pilot project for one of its dams. The facility is a concrete-faced rockfill dam constructed in the early 20th century.
The RIDM work on this facility thus far has included a Semi-Quantitative Risk Analysis and Quantitative Risk Analysis Workshops. Assessments have included stochastic hydrology, assessment of potential overtopping- induced embankment erosion in the probable maximum flood, the potential for spillway erodibility, facing slab stability, potential for deformation of the dam under seismic loading, and HEC-LifeSim evaluation of downstream consequences. The results of these evaluations have provided a clearer understanding of dam safety issues for the owner. Previously, potential failure mode analysis processes had identified several potential dam safety concerns. The RIDM process expedited an identification of a single failure model as driving the risk and allowed for the assessment of a range of mitigation options. Additionally, the application of the Interim FERC Risk Guidelines has assisted in evaluating the proposed risk methodologies and developing a group of facilitators and subject matter experts who can serve on future risk assessment projects. A number of lessons were learned during the course of the project regarding the overall RIDM process which will be informative for those in industry who plan on applying similar approaches in the future.
Use of a Slot Cut Approach During a Major Landslide Hazard Reduction Project at a Frank R. Bowerman Landfill
Presenter: Yonas Zemuy
CoAuthors: Chris Conkle, Alexander Stern, and Saverio Siciliano, Geosyntec; Kevin Hanson, OC Waste and Recycling
Abstract: Solid waste landfills are frequently located in areas where continued development requires addressing hazards posed by static or seismic slope instabilities. Slot-cut excavations have been widely used to maintain stable slopes during excavations adjacent to structures or at the toe of steep slopes. It is well known that the observed improvement of slope performance in slot-cut excavations over what would be expected based on two-dimensional evaluations is due to the contribution of out-of-plane resistance or the three-dimensional (3D) effect on slope stability. The evaluation of slot-cut stability in practice, however, is often based on a highly simplified single-block wedge analysis valid only for simple slope geometry and homogeneous soil conditions.
This work included the remedial design and construction for a major landslide in formational materials at the Frank R. Bowerman Landfill in Orange County, California, that incorporated the slot cut approach. The construction of this remediation was completed in 2018. Plans called for a staged development with segmental excavation and buttress filling along the toe of an existing creeping landslide. The segmental excavation included 42 slots that are each a maximum 50-ft wide along the toe of landslide slope.
Using 3-D slope stability software, the critical slots along the toe of the landslide were evaluated to provide input into the project specifications. The project team evaluated the landslide from several different orientations (i.e., backcut, side cut in landslide debris, and side slopes of engineered fill). Based on these evaluations, recommendations regarding minimum and interim fill elevations were needed prior to starting adjacent slots. Ultimately a slot cut approach was successfully used to construct the project. Geotechnical monitoring of the landslide movements during construction informed the execution.
About the event: ASCE Lifelines Conference 2021-2022: San Francisco Earthquake Conference on Lifeline Engineering – 50 Years of Lifeline Engineering