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[[Category:Geotechnical Geology]]
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Example of a slope stability analysis. ([https://en.wikipedia.org/wiki/Slope_stability_analysis Wikipedia])
Example of a slope stability analysis.  
(Image Source: [https://en.wikipedia.org/wiki/Slope_stability_analysis Wikipedia])
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Stability of the upstream and downstream slopes of an earth embankment dam is essential to the dam’s safe operation. Unsatisfactory slope performance includes the following categories of slope movement: shear failure, surface sloughing, excessive deformation, liquefaction, and any other types of slope movements <ref name="Slope Stability">[[Slope Stability (EM 1110-2-1902)| EM 1110-2-1902 Slope Stability, USACE, 2003]]</ref>. Slope movements that do not cause an immediate failure of the dam can require significant maintenance, and it left unrepaired, can lead to an eventual failure. Proper analysis and design of the embankment slopes, coupled with close monitoring and prompt maintenance or repairs to any moved sections of the slope(s) are key to preventing failure or a major incident from occurring.  
[[Stability]] of the upstream and downstream slopes of an earth embankment dam is essential to the dam’s safe [[operation]]. Unsatisfactory slope performance includes the following categories of slope movement: shear failure, surface sloughing, excessive deformation, liquefaction, and any other types of slope movements <ref name="Slope Stability">[[Slope Stability (EM 1110-2-1902)| Slope Stability (EM 1110-2-1902), USACE, 2003]]</ref>. Slope movements that do not cause an immediate failure of the dam can require significant maintenance, and if left unrepaired, can lead to an eventual failure. Proper analysis and design of the embankment slopes, coupled with close monitoring and prompt maintenance or repairs to any moved sections of the slope(s) are key to preventing failure or a major incident from occurring.  


“The stability of dams and slopes must be evaluated utilizing pertinent geologic information and information regarding in situ engineering properties of soil and rock materials. The geologic information and site characteristics that should be considered include: (1) groundwater and seepage conditions; (2) lithology, stratigraphy, and geologic details disclosed by borings and geologic interpretations; (3) maximum past overburden at the site as deduced from geologic evidence; (4) structure, including bedding, folding, and faulting; (5) alteration of materials by faulting; (6) joints and joint systems; (7) weathering; (8) cementation; (9) slickensides; (10) field evidence relating to slides, earthquake <br> activity, movement along existing faults, and tension jointing”.<ref name="Slope Stability" />
==Loading Conditions==
“Evaluation of slope stability requires establishing the conditions, called ‘design conditions’ or ‘[[Loading Conditions|loading conditions]],’ to which the slope may be subjected during its life, and performing analyses of stability for each of these conditions. There are four design conditions that must be considered for dams:  
#[[Stability During and at the End of Construction|During and at the end of construction]],  
#[[Stability During Steady State Seepage Conditions|Steady state seepage]] (both normal and [[Flood Conditions|flood conditions]]),  
#[[Stability During Sudden Drawdown|Sudden drawdown]], and  
#[[Stability During an Earthquake|Earthquake loading]].  


“Evaluation of slope stability requires: (a) establishing the conditions, called ‘design conditions’ or ‘loading conditions,’ to which the slope may be subjected during its life, and (b) performing analyses of stability for each of these conditions. There are four design conditions that must be considered for dams: (1) during and at the end of construction, (2) steady state seepage, (3) sudden drawdown, and (4) earthquake loading. The first three conditions are static; the fourth involves dynamic loading”.<ref name="Slope Stability" />
 
"The first three conditions are static; the fourth involves dynamic loading”.<ref name="Slope Stability" />
 
==Types of Information Needed==
The key inputs to any slope stability model are [[Soil/Rock Strength Characterization for Stability Analysis|unit weights and soil strength parameters]]. “The stability of dams and slopes must be evaluated utilizing pertinent geologic information and information regarding in situ [[engineering]] properties of soil and rock materials. The geologic information and site characteristics that should be considered include:  
 
#"[[groundwater]] and seepage conditions;
#"lithology, stratigraphy, and geologic details disclosed by borings and geologic interpretations;
#"maximum past overburden at the site as deduced from geologic evidence;
#"structure, including bedding, folding, and faulting;
#"alteration of materials by faulting;
#"joints and joint systems;
#"weathering;
#"cementation;
#"slickensides;
#"field evidence relating to slides, earthquake activity, movement along existing faults, and tension jointing”.<ref name="Slope Stability"/></br></br>
 
==Other Guidance==
A critical aspect of any [[engineering]] analysis is communication. There are a variety of slope stability 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]]. Items specific to slope stability analysis that should be considered in advance of any modeling effort are summarized here: [[Pre-Modeling Communication: Slope Stability Model Considerations]].


==Examples==
==Examples==
{{Website Icon}}
{{Website Icon}} [https://damfailures.org/lessons-learned/earth-and-rockfill-embankment-dams-must-be-stable-under-the-full-range-of-anticipated-loading-conditions/ Learn more about the need for stable slopes at earth and rockfill dams (DamFailures.org)]
 
==Best Practices Resources==
==Best Practices Resources==
{{Document Icon}} [[Slope Stability (EM 1110-2-1902)]]
{{Document Icon}} [[Technical Release 210-60: Earth Dams and Reservoirs | Technical Release 210-60: Earth Dams and Reservoirs, NRCS]]
{{Document Icon}} [[Design Standards No. 13: Embankment Dams (Ch. 4: Static Stability Analysis) | Design Standards No. 13: Embankment Dams (Ch. 4: Static Stability Analysis), USBR]]
{{Document Icon}} [[Engineering Guidelines for the Evaluation of Hydropower Projects: Chapter 4- Embankment Dams | Engineering Guidelines for the Evaluation of Hydropower Projects: Chapter 4- Embankment Dams, FERC]]
{{Document Icon}} [[Slope Stability (EM 1110-2-1902) | Slope Stability (EM 1110-2-1902), USACE]]
 
==Trainings==
==Trainings==
{{Video Icon}}
{{Video Icon}} [[On-Demand Webinar: Strength Selection for Static Slope Stability Analysis]]
{{Video Icon}} [[On-Demand Webinar: Seismic Stability Evaluation of Earth Dams]]
{{Website Icon}} [[Technical Seminar: Stability Analysis of Embankment Dams]]


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Latest revision as of 19:49, 27 August 2024

Example of a slope stability analysis.

(Image Source: Wikipedia)

Stability of the upstream and downstream slopes of an earth embankment dam is essential to the dam’s safe operation. Unsatisfactory slope performance includes the following categories of slope movement: shear failure, surface sloughing, excessive deformation, liquefaction, and any other types of slope movements [1]. Slope movements that do not cause an immediate failure of the dam can require significant maintenance, and if left unrepaired, can lead to an eventual failure. Proper analysis and design of the embankment slopes, coupled with close monitoring and prompt maintenance or repairs to any moved sections of the slope(s) are key to preventing failure or a major incident from occurring.

Loading Conditions

“Evaluation of slope stability requires establishing the conditions, called ‘design conditions’ or ‘loading conditions,’ to which the slope may be subjected during its life, and performing analyses of stability for each of these conditions. There are four design conditions that must be considered for dams:

  1. During and at the end of construction,
  2. Steady state seepage (both normal and flood conditions),
  3. Sudden drawdown, and
  4. Earthquake loading.


"The first three conditions are static; the fourth involves dynamic loading”.[1]

Types of Information Needed

The key inputs to any slope stability model are unit weights and soil strength parameters. “The stability of dams and slopes must be evaluated utilizing pertinent geologic information and information regarding in situ engineering properties of soil and rock materials. The geologic information and site characteristics that should be considered include:

  1. "groundwater and seepage conditions;
  2. "lithology, stratigraphy, and geologic details disclosed by borings and geologic interpretations;
  3. "maximum past overburden at the site as deduced from geologic evidence;
  4. "structure, including bedding, folding, and faulting;
  5. "alteration of materials by faulting;
  6. "joints and joint systems;
  7. "weathering;
  8. "cementation;
  9. "slickensides;
  10. "field evidence relating to slides, earthquake activity, movement along existing faults, and tension jointing”.[1]

Other Guidance

A critical aspect of any engineering analysis is communication. There are a variety of slope stability 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. Items specific to slope stability analysis that should be considered in advance of any modeling effort are summarized here: Pre-Modeling Communication: Slope Stability Model Considerations.

Examples

Learn more about the need for stable slopes at earth and rockfill dams (DamFailures.org)

Best Practices Resources

Technical Release 210-60: Earth Dams and Reservoirs, NRCS

Design Standards No. 13: Embankment Dams (Ch. 4: Static Stability Analysis), USBR

Engineering Guidelines for the Evaluation of Hydropower Projects: Chapter 4- Embankment Dams, FERC

Slope Stability (EM 1110-2-1902), USACE

Trainings

On-Demand Webinar: Strength Selection for Static Slope Stability Analysis

On-Demand Webinar: Seismic Stability Evaluation of Earth Dams

Technical Seminar: Stability Analysis of Embankment Dams


Citations:

  1. ↑ 1.0 1.1 1.2 Slope Stability (EM 1110-2-1902), USACE, 2003


Revision ID: 8039
Revision Date: 08/27/2024

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