Seismic

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Learn more about the failure of Lower San Fernando Dam during a seismic event at DamFailures.org

“The scope of the seismic hazard study at a site depends on the seismicity of a region or site-specific considerations, the types of structures involved, and the consequences of failure. The design and evaluation of dams for earthquake loading should be based on a comparable level of study and analysis for each phase of the study (seismotectonic, geological, site, geotechnical, and structural investigations) and that level of study should reflect both the criticality of the structure and the complexity of the analysis procedures".

"Risk management and risk analysis can be used in making seismic evaluation of dams. These methods may be applied to help accomplish the following: prioritize safety evaluations when considering a large number of dams; evaluate the benefits of alternative remedial measures; select load levels; and evaluate the structural response. Risk management and risk analysis tools may also be applied as a framework for the overall seismic evaluation leading to the final decisions. The application of risk assessment procedures in a comprehensive and quantitative manner is used as a tool by various agencies to improve the quality and consistency of decisions on the seismic safety of structures. It is recognized that risk is considered in the application of engineering judgement even when more formal risk analysis procedures are not employed".

Design Criteria

A Seismic Hazard Analysis (SHA) is an assessment of naturally occurring earthquakes using faults or past earthquakes to predict the hazard. The purpose of conducting a seismic hazard analysis is to develop seismic design criteria for use in evaluating the seismic response of a given structure or facility. Presently, there are three ways by which the design requirements can be ascertained: use of local building codes; conducting a Deterministic Seismic Hazard Analysis (DSHA) Deterministic Seismic Analysis; or performing a Probabilistic Seismic Hazard Analysis (PSHA) Probabilistic Seismic Analysis.

Determining which of the three above mentioned analyses that need to be completed depends on the owner or regulatory commission in charge of the structure that is being designed. It is important to recognize that different agencies, local cities, counties, states or countries could have separate design guidelines that may need to be reviewed to ensure that all guidelines are being followed.

Types of Seismic Evaluations

After the applicable codes and regulatory guidelines are determined, the next step is to understand what results are expected from a seismic hazard analysis. It is often helpful to discuss how the results will be used with the lead structural engineer, geologist or geotechnical engineer. Certain projects may need to have inputs for a liquefaction analysis; slope stability analysis or perhaps reservoir triggered seismicity is a concern. It is always important to understand the studies that may need to be completed before jumping into a seismic hazard analysis.

In the feasibility level analysis pseudo-static coefficients and simplified methods of deformation are sometimes used to estimate deformation. The preliminary design normally includes more complicated analyses, which sometimes requires a site specific spectrum or include development of time histories. Finally, detailed design in many instances includes a finite element method (FEM) analyses which requires time histories. In addition, foundation studies may require the use of SHAKE to deconvolute the time histories to a level of shaking experienced beneath the foundation.

A critical aspect of any engineering analysis is communication. There are a variety of seismic modeling approaches and methodologies, and it is important to owners, consultants, and regulators that clear communication is integrated in the process. General guidance and recommendations regarding both pre- and post-modeling communication are provided on this page: Modeling Communication.

Hazard Analysis

Seismic Source Characterization

• Geologic and Tectonic Setting
• Seismic Source Characterization

Ground Motion Attenuation Relationships

• Ground Motion Characterization

Dam-specific Considerations

• Reservoir-triggered Seismicity
• Seiches

Performance Evaluation

• Site Response Analysis
• Static Equivalent Analysis
• Dynamic Analysis
• Soil-Structure Interaction
• Performance-based Seismic Design

Monitoring and Instrumentation

The most common seismic-specific monitoring/instrumentation is to record acceleration at a dam site. The data from these recordings can be used to evaluate the dynamic response of a dam and typically measures velocity and acceleration in three mutually-perpendicular directions. The location of instrumentation is incredibly important to determine accelerations on the structure, at the foundation, and the abutments. Understanding site-response at the dam is vital to interpreting recorded accelerations. To prevent accumulation of unwanted data, most instruments will be triggered to measure under relatively small accelerations.

Following any significant seismic event, the dam structure should be inspected. An action-level threshold should be pre-determined depending on the vulnerability of the dam, downstream hazard, and level of shaking. Post-earthquake inspections focus on the earthquake-induced damage, signs of distress, and any changes to the foundation or dam that could indicate a problem. Embankments are typically evaluated for cracking, slumping, and other signs of movement. Concrete dams are checked for signs of structural distress such as cracking or spalling and movement. Spillways and outlets are checked for signs of instability and to ensure they are clear of debris and fully functional. Seepage is evaluated for changes in quantity, quality, and new locations of seepage. It is common for instrumentation to change suddenly after an earthquake and enhanced monitoring is often necessary following the event.

• Monitoring
• Instrumentation

Case Studies

Learn more about the importance of accounting for seismic loadings in dam designs (DamFailures.org)

Learn more about the failure of Lower San Fernando Dam during a seismic event (DamFailures.org)

Best Practices

Engineering Guidelines for the Evaluation of Hydropower Projects: Chapter 13- Evaluation of Earthquake Ground Motions, FERC

Design Standards No. 13: Embankment Dams (Ch. 13: Seismic Analysis and Design), USBR

Earthquake Design and Evaluation of Concrete Hydraulic Structures (EM 1110-2-6053), USACE

Federal Guidelines for Dam Safety: Earthquake Analyses and Design of Dams (FEMA P-65), FEMA

Response Spectra and Seismic Analysis for Concrete Hydraulic Structures (EM 1110-2-6050), USACE

USBR Best Practices Chapters - Seismic Sections

Chapter B-2 Seismic Hazard Analysis , USBR

Chapter D-8 Seismic Risks for Embankments , USBR

Chapter E-6 Seismic Pier Failure , USBR

Chapter E-7 Seismic Evaluation of Retaining Wall , USBR

Chapter G-3 Seismic Failure of Spillway Radial (Tainter) Gates , USBR

Standards and Guidelines

Analysis of Seismic Deformations of Embankment Dams , USSD Committee on Earthquakes Sub-Committee on Seismic Deformation Analysis of Embankment Dams, August 2022, USDS

Dam Modifications to Improve Performance During Strong Earthquakes-2003, USSD Committee on Earthquakes, February 23, 2003, USDS

ICOLD (International Commission on Large Dams) Bulletins: (ICOLD Bulletins are free for members of ICOLD or USSD).

Inspection of dams following earthquake – Guidelines. ICOLD Bulletin 166, 2016. Revision of Bulletin 062 (1988) , ICOLD

Selecting seismic parameters for large dams – Guidelines. ICOLD Bulletin 148, 2016 (Revision of Bulletin 72), ICOLD

Selecting Seismic Parameters for Large Dams – Guidelines, CIGB ICOLD Bulletin 72, 2010, - Superseded, ICOLD

Reservoirs and seismicity - State of knowledge, ICOLD Bulletin 137, 201, ICOLD

Seismic design and evaluation of structures appurtenant to dams- Guidelines, ICOL Bulletin 123, 2002, ICOLD

Design features of dams to resist seismic ground motion - Guidelines and case histories, ICOL Bulletin 120, 2001, ICOLD

Seismic observation of dams-Guidelines and case studies - Guidelines and case studies. ICOL Bulletin 113, 1999, ICOLD

State Guides

California

State Water Project - Seismic Loading Criteria Report, September 2012, California Department of Water Resources, Division of Engineering

CALTRANS Geotechnical Manual – Design Acceleration Response Spectrum, CALTRANS

California DSOD Protocols

Montana

Technical Note 5 – Simplified Seismic Analysis Procedure for Montana Dams, November 30, 2020, Montana Department of Natural Resources and Conservation

Washington

Dam Safety Guidelines Part IV: Dam Design and Construction, July 1993 (Chapter 2), Water Resources Program, Dam Safety Office

Software Tools

Only free tools listed here:

RMC (USACE Risk Management Center) has spreadsheet tools for evaluation of Site Classification, Seismic Hazard Curves, Liquefaction, Lateral Spreading Displacement and Empirical Crest Deformation

DEEPSOIL is a unified 1D equivalent linear and nonlinear site response analysis platform

SLAMMER is a Java program that facilitates performing a variety of sliding-block analyses to evaluate seismic slope performance. Functionalities include both rigorous and simplified analyses of rigid sliding blocks (i.e. Newmark analysis) and flexible sliding blocks (i.e. decoupled and fully coupled approaches).

Strata performs 1D equivalent-linear site response analysis in the frequency domain using time domain input motions or random vibration theory (RVT) methods, and allows for randomization of the site properties

Quad4M is a 2D seismic response analysis tool for soil structures based on equivalent-linear soil model (2D version of SHAKE)

SHAKE is a 1D seismic response analysis tool based on equivalent-linear soil model

Training Materials

Seismic Analysis of Dams

On-Demand Webinar: Current Trends in the Seismic Analysis of Embankment Dams

On-Demand Webinar: Seismic Stability Evaluation of Earth Dams

On-Demand Webinar: Lessons Learned Regarding Seismic Deformation Analyses of Embankment Dams from Re-Evaluation of the Upper and Lower San Fernando Dams Performance Case Histories

On-Demand Webinar: Site Investigation and Parameter Development for Seismic Deformation Analyses of Embankment Dams and Levees

Technical Seminar: Earthquake Engineering for Embankment Dams

Dynamic Site Response

On-Demand Webinar: Earthquake Hazards, Ground Motions and Dynamic Response

Nonlinear Site Response

Ground Motion Parameters and Signal Processing

Citations

Citations:

Revision ID: 8063
Revision Date: 09/04/2024