September 13, 2022

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Geosyntec to Present Multiple Technical Papers at ASDSO 2022

Geosyntec staff will make a significant technical contribution at the Association of State Dam Safety Officials (ASDSO) Conference at the Baltimore Convention Center in Baltimore, Maryland, on September 18 through September 22, 2022.

Geosyntec staff have coauthored and will present six technical papers, in addition to moderating multiple technical sessions. Our professional staff actively participating at ASDSO 2022 conference include John Barrett, Emily Campbell, P.E., Fred Chandler, P.G., Christopher Conkle, P.E., G.E., Lucas de Melo, Ph.D., P.E., Conrad Ginther, P.E., Christie Hale, PhD., Mehdi Khalili, Joseph Kula, Zachary Mickel, P.E., Derek Morley, P.E., Glenn Rix, Ph.D., P.E., Missy Setz, P.E., and Onur Tastan, PhD., P.E..

Geosyntec is a silver sponsor of the conference.

Founded in 1984, the ASDSO works to improve the condition and safety of dams and lower the risk of dam failures by educating members, supporting state dam safety programs, and fostering a unified dam safety community. The 2022 ASDSO conference will include over 100 technical sessions, two general sessions, and three workshops, as well as two field tours.

Moderated Sessions and Presentations

Session 11—Focus on Seismic Issues
Presentation Title: Framework for Seismic Risk Analysis of Embankment Dams
Speakers: Glenn Rix, Martin W. McCann, Jr. (Jack R. Benjamin and Associates, Inc.)
Time: Tuesday, September 20 at 10:30 a.m. EDT
Abstract: Earthquakes pose a unique threat to embankment dams. Earthquake ground motions can produce embankment instability, deformations that lead immediately to overtopping or that can initiate multiple modes of failure, and liquefaction in the embankment or foundation that can result in significant damage or failure and uncontrolled release of the reservoir. An earthquake is also unique from the perspective that prior warning is not available (unlike a flood event) and other systems (e.g., spillway gates, outlets, operators) may also suffer damage or failure, compromising or preventing post-earthquake mitigation efforts. On a regional scale, a moderate to large earthquake can impact other dams (upstream and downstream), produce other hazards such as landslides, reservoir seiche, surface rupture, and impacts to emergency services. Seismic risks can thus be an important contributor to the overall risk profile of a dam. Furthermore, differences in seismic hazard between the eastern and western United States due to differences in the frequency of occurrence of earthquakes and ground motion attenuation also impact seismic risk. This paper presents a framework for conducting seismic risk analyses for embankment dams, including the evaluation of aleatory and epistemic uncertainties and their propagation through the risk quantification. Each of the elements of a seismic risk analysis—including estimation of the seismic hazard, the assessment of the seismic fragility of an embankment for multiple potential failure modes, systems analysis, dam breach and inundation assessment, and downstream consequence analysis—is subject to multiple sources of uncertainty. In this paper we present a framework for identifying and evaluating sources of aleatory and epistemic uncertainty. The framework defines aleatory and epistemic uncertainties, how they are modeled in a risk analysis, and how the uncertainties in the different parts of the analysis are combined to estimate seismic risk (e.g., frequency of uncontrolled release of the reservoir). The evaluation of the different sources of uncertainty and their incorporation in each part of the analysis - seismic hazard, results of seismic deformation analyses, the identification of potential failure modes into the quantification of seismic risk (frequency of uncontrolled release of the reservoir) is demonstrated. The seismic risk framework presented in this paper is demonstrated for dams located in both the eastern and western United States.

Presentation Title: How Do You Perform A DSHA For a Distributed Seismicity Source?
Speakers: Christie Hale, Glenn Rix, Onur Tastan
Time: Tuesday, September 20 at 10:30 a.m. EDT
Abstract: Seismic hazard assessments are conducted to estimate ground motions and establish response spectra for use in engineering evaluations of dams, and many guidance documents recommend or require a deterministic seismic hazard analysis (DSHA) as part of the seismic hazard assessment (e.g., FERC Chapter 13, 2018; USACE ER 1110-2-1806, 2016). A fundamental step in the DSHA is to define the deterministic scenarios in terms of the earthquake magnitude, distance, and ground motion level. When the sources capable of producing ground motions at the dam site consist of known faults, the selection of magnitude and distance are unambiguous and the slip rate can be used to inform the selection of a ground motion level; however, when the seismic sources consist of distributed seismicity sources without mapped faults, the selection of a single deterministic magnitude, distance, and ground motion level are ambiguous because the scenarios for a distributed seismicity source are inherently comprised of a broad distribution and the activity of the source is not characterized by a slip rate. With guidance documents geared toward the known fault case, practitioners and owners are left asking: how do you perform a DSHA for a distributed seismicity source? This paper describes different approaches that we have seen and applied in practice, explores whether there is an objective approach, and presents examples from seismic hazard assessments conducted in the Central and Eastern United States.

Session 21—Rehabilitation Methods and Materials
Presentation Title: Performance of the Boone Dam during Reservoir Filling following Remediation
Speakers: John Barrett, Chris Saucier (Tennessee Valley Authority)
Time: Tuesday, September 20 at 3:30 p.m. EDT
Abstract: Following observations indicative of active internal erosion in 2014, the Tennessee Valley Authority (TVA) lowered the reservoir at the Boone Hydroelectric Plant in order to reduce dam safety risks until permanent improvements could be implemented. Following investigations in 2014 and early 2015, the TVA adopted a composite seepage barrier remedial solution, the construction of which was completed in early 2021. The composite seepage barrier was composed of low-mobility grouting (LMG), high-mobility grouting (HMG), and a concrete cutoff wall constructed by secant pile construction. TVA began refilling the reservoir in March 2021 for the first time since restricting reservoir levels following the events described above in 2014. The objective of this paper is to document some of the lessons learned collected from the execution of project from 2016 through 2021 and to describe the performance of the embankment dam during reservoir filling. The paper is organized to (i) summarize the tools that were used to reduce seepage beneath the embankment dam, (ii) describe their efficiency at reducing seepage as interpreted by the extensive instrumentation program at the site; and (iii) highlight the overall response and performance of the dam during each phase of the project.

Session 22—Developing Your Risk Toolbox
Presentation Title: Potential Failure Mode Screening Analyses
Speakers: Martin W. McCann, Jr. (Jack R. Benjamin and Associates, Inc.), Glenn Rix, Thomas Westover (Cornforth Consultants, Inc.)
Time: Tuesday, September 20 at 3:30 p.m. EDT
Abstract: An important step in a risk analysis to support dam safety evaluations is the identification of potential failure modes (PFMs), either as part of a Potential Failure Mode Analysis (PFMA) or as an early step in a risk analysis. In conventional PFMAs, the participants are often asked to subjectively assess the likelihood of a PFM, and judged whether it could be an important contributor to the risk of failure of the dam or its appurtenant structures. Such ad hoc subjective approaches are subject to uncertainties in the available information at the time, alternative interpretations of the experts. One quantitative approach that is used is based on a simplified calculation based on (i) selecting an annual frequency of exceedance (AFE), (ii) obtaining the hazard intensity (e.g., peak ground acceleration or headwater elevation) associated with the selected AFE, and (iii) estimating the probability of failure conditioned on the hazard intensity. The annual probability of failure (APF) is calculated as the product of the AFE and conditional probability of failure. This calculation can often underestimate the risk (i.e., APF) associated with the PFM and may lead to improper screening from further analyses and evaluations. In this paper we recommend a transparent, quantitative approach to risk screening of PFMs that are associated with external hazards such as earthquakes or floods. The screening approach is based on the simple idea that PFMs do not need to be carried forward into a risk analysis if can be shown through a clear, quantitative assessment that provides a risk-informed defensible basis to screen PFMs from further evaluation. The recommended approach to screening PFMs provides an estimate of the minimum required capacity of the dam PFMs or appurtenant structure PFMs that is needed to achieve a target APF. The analysis considers the overall target performance goal (e.g., frequency of uncontrolled release of the reservoir) for the dam system, and the potential that multiple failure modes may in aggregate contribute to the total frequency of URR. The calculations are also simple and can readily be implemented as a closed-form solution or spreadsheet calculations. This approach provides a more accurate and robust method of screening PFMs.

Session 29—Near Miss
Moderator: Zachary Mickel
Time: Wednesday, September 21 at 10:30 a.m. EDT

Session 30—Advanced Geo Tech
Moderator: Joseph Kula
Time: Wednesday, September 21 at 10:30 a.m. EDT

Session 33—Federal Funding and Communications Initiatives
Presentation Title: Case Study: A Small Hydroelectric Dam Navigating FEMA's Hazard Mitigation Program
Speakers: Emily Campbell, John Barrett, and Matt Bardol
Time: Wednesday, September 21 at 1:30 p.m. EDT
Abstract: In May of 2020, Mid-Michigan experienced significant rainfall events that resulted in the catastrophic failure of the Edenville and Sanford Dams. The City of Beaverton (City) operates a small concrete, hydroelectric power dam directly upstream of the Edenville dam and also suffered damages from flooding, though it did not breach or fail. The damages included scour downstream of the dam, buckling of a steel retaining wall downstream of the spillway, and excessive vibrations inside the powerhouse. Following the event, the City engaged Geosyntec Consultants (Geosyntec) to assist them with developing plans to repair the damage, as well as long-term planning for the operation and maintenance of the facility. Geosyntec has worked closely with the City as it navigated the repair process set forth by the Federal Emergency Management Agency's (FEMA's) Hazard Mitigation Program (HMP). This paper presents an overview of the May 2020 Mid-Michigan flood event, the impact on the City of Beaverton Dam, lessons learned while navigating FEMA's HMP funding process, and the perspective from a small dam owner.

Session 38—Top Tips and Tools in Construction Management
Presentation Title: Case Studies in Construction Quality Control / Quality Assurance Methods for Seepage Cutoff Walls
Speakers: Joseph Kula, Conrad Ginther, Jamey Rosen, John Barrett, Fred Chandler, Veronica Barredo, (TVA), Hector Davila (Bauer Foundation Corp.)
Time: Wednesday, September 21 at 3:30 p.m. EDT
Abstract: Seepage barriers or cutoff walls are a standard construction method for reducing seepage and mitigating against internal erosion associated with embankment dams and levees. Innovation by specialty contractors over the last 20 years has resulted in advancements in production rates, achievable wall depths, and feasibility of construction in difficult foundation conditions. Evolving construction techniques, many proprietary, include improvements in excavation equipment, materials, and backfill placement techniques. The advancements in cutoff wall construction have led to demand for equally innovative technologies for construction quality control and quality assurance (CQC/CQA). The primary wall attributes requiring monitoring and verification for conformance with design criteria and contract documents include: - wall geometry: horizontal position, wall minimum thickness, depth, verticality, and overlap of adjacent elements - homogeneity of the wall materials and structural continuity including sound joints between wall elements and avoidance of discontinuities - material properties including unit weight, strength, durability, deformability, and permeability This paper will present case studies of cutoff wall construction at Boone Dam (owned by the TVA) and the Herbert Hoover Dike (owned by the United States Army Corps of Engineers) with specific applications of current best practices for QA/QC monitoring and verification of cutoff wall construction. Lessons learned from these projects include the benefits and challenges with the use of multiple methods of verifying excavation geometry (i.e., verticality and overlap between elements), and the need for integration of field observations from excavation and backfill activities into real-time web-based Information Management Systems during construction.

Poster Lightning Talk: Project Execution Risk vs. Infrastructure Performance Risk: A Critical Distinction for Dam Safety
Speakers: Derek Morley, Brian Hubel (U.S. Army Corps of Engineers)

More Information

About the event: Dam Safety 2022 | Association of State Dam Safety
About ASDSO: Association of State Dam Safety
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