Underseepage: Difference between revisions
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[[Category:Foundation Evaluation]] | |||
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"Flow of water through soil can lead to movement of the soil grains. Continued movement is erosion. Many factors affect whether soil grains will move or not, including hydraulic gradient, soil plasticity, particle size, capillary tension, cementation, and others."<ref name="DS13-8">[[Design Standards No. 13: Embankment Dams (Ch. 8: Seepage) | Design Standards No. 13: Embankment Dams (Ch. 8: Seepage) | "Flow of water through soil can lead to movement of the soil grains. Continued movement is erosion. Many factors affect whether soil grains will move or not, including hydraulic gradient, soil plasticity, particle size, capillary tension, cementation, and others."<ref name="DS13-8">[[Design Standards No. 13: Embankment Dams (Ch. 8: Seepage) | Design Standards No. 13: Embankment Dams (Ch. 8: Seepage), USBR, 2014]]</ref> | ||
"A review of historical dam failures indicates that nearly half of all failures of [[Embankment Dams|embankment dams]] have been a result of seepage-induced internal erosion. Additional failures due to high pore pressures or saturated slopes, both attributable to seepage water, add to the list of seepage-related historical failures. Since all [[soils]] are erodible to some extent, [[Embankment Dams|embankment dams]] are potentially susceptible to failure due to seepage. In order to evaluate new or existing dams, with respect to safety against seepage, and design defensive measures to mitigate the effects of seepage, it is important to understand the various modes of failure that can occur due to reservoir seepage acting on an embankment or its foundation."<ref name="DS13-8"/> | "A review of historical dam failures indicates that nearly half of all failures of [[Embankment Dams|embankment dams]] have been a result of seepage-induced internal erosion. Additional failures due to high pore pressures or saturated slopes, both attributable to seepage water, add to the list of seepage-related historical failures. Since all [[soils]] are erodible to some extent, [[Embankment Dams|embankment dams]] are potentially susceptible to failure due to seepage. In order to evaluate new or existing dams, with respect to safety against seepage, and design defensive measures to mitigate the effects of seepage, it is important to understand the various modes of failure that can occur due to reservoir seepage acting on an embankment or its foundation."<ref name="DS13-8"/> | ||
"Observations related to seepage through an earth embankment or its foundation may give an early indication of the nature, location, and severity of potential failure modes (PFMs) that may already have initiated or could initiate at higher reservoir levels. For example, vigorously flowing sand boils discharging sediment near the downstream toe of an embankment may indicate that backward erosion piping in the foundation has already initiated and that it has the potential for rapid progression. Likewise, concentrated, clear seepage at an abutment groin may be an indication of a preferential flow path through the abutment, which could provide an avenue for internal erosion at higher gradients."<ref name="FEMAP1032">[[Evaluation and Monitoring of Seepage and Internal Erosion (FEMA P-1032) | Evaluation and Monitoring of Seepage and Internal Erosion (FEMA P-1032) | "Observations related to seepage through an earth embankment or its foundation may give an early indication of the nature, location, and severity of potential failure modes (PFMs) that may already have initiated or could initiate at higher reservoir levels. For example, vigorously flowing sand boils discharging sediment near the downstream toe of an embankment may indicate that backward erosion piping in the foundation has already initiated and that it has the potential for rapid progression. Likewise, concentrated, clear seepage at an abutment groin may be an indication of a preferential flow path through the abutment, which could provide an avenue for internal erosion at higher gradients."<ref name="FEMAP1032">[[Evaluation and Monitoring of Seepage and Internal Erosion (FEMA P-1032) | Evaluation and Monitoring of Seepage and Internal Erosion (FEMA P-1032), FEMA, 2015]]</ref> | ||
"Seepage collection and monitoring systems should be designed with all failure modes in mind that may reasonably be anticipated at a particular structure site, given its unique geologic characteristics and design features. Ideally, all needed seepage measurement and monitoring systems should already be in place and available to collect seepage information from the [[First Filling | first filling]] on, but of course new seepage areas can emerge at any time. Once water is impounded in the reservoir, all seepage-related phenomena should be evaluated with reference to PFMs of which they could be indicators. Early identification of PFMs that may be at work can facilitate the undertaking of emergency or remedial actions that need to be performed on short notice."<ref name="FEMAP1032" /> | "Seepage collection and monitoring systems should be designed with all failure modes in mind that may reasonably be anticipated at a particular structure site, given its unique geologic characteristics and design features. Ideally, all needed seepage measurement and monitoring systems should already be in place and available to collect seepage information from the [[First Filling and Monitoring | first filling]] on, but of course new seepage areas can emerge at any time. Once water is impounded in the reservoir, all seepage-related phenomena should be evaluated with reference to PFMs of which they could be indicators. Early identification of PFMs that may be at work can facilitate the undertaking of emergency or remedial actions that need to be performed on short notice."<ref name="FEMAP1032" /> | ||
"Measuring seepage quantity and quality provides several important benefits: | "Measuring seepage quantity and quality provides several important benefits: | ||
# ''Comparison with Design:'' Measurements of actual seepage can be compared with seepage rates assumed or calculated during design to evaluate whether the dam and its various seepage control systems are functioning as intended (e.g., a foundation cutoff system or an embankment or foundation drain). | # '''Comparison with Design:''' Measurements of actual seepage can be compared with seepage rates assumed or calculated during design to evaluate whether the dam and its various seepage control systems are functioning as intended (e.g., a foundation cutoff system or an embankment or foundation drain). | ||
# ''Identifying Changes with Time:'' The appearance of unexpected seepage or changes in seepage quantity or quality over time can alert the dam owner to potential problems occurring within the embankment or foundation and allow for the implementation of corrective measures in a timely manner."<ref name="FEMAP1032" /> | # '''Identifying Changes with Time:''' The appearance of unexpected seepage or changes in seepage quantity or quality over time can alert the dam [[owner]] to potential problems occurring within the embankment or foundation and allow for the implementation of corrective measures in a timely manner."<ref name="FEMAP1032" /></br></br> | ||
==Mitigation Measures== | ==Mitigation Measures== | ||
* [[Relief | * [[Relief Wells]] | ||
* [[Cutoff]] | * [[Cutoff]] | ||
* [[Grouting]] | * [[Grouting]] | ||
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==Examples== | ==Examples== | ||
{{Website Icon}} [https://damfailures.org/case-study/teton-dam-idaho-1976/ Learn about the | {{Website Icon}} [https://damfailures.org/case-study/teton-dam-idaho-1976/ Learn about the underseepage and internal erosion at Teton Dam that ultimately led to its failure (DamFailures.org)] | ||
==Best Practices Resources== | ==Best Practices Resources== | ||
{{Document Icon}} [[Evaluation and Monitoring of Seepage and Internal Erosion (FEMA P-1032) | Evaluation and Monitoring of Seepage and Internal Erosion (FEMA P-1032) | {{Document Icon}} [[Evaluation and Monitoring of Seepage and Internal Erosion (FEMA P-1032) | Evaluation and Monitoring of Seepage and Internal Erosion (FEMA P-1032), FEMA]] | ||
{{Document Icon}} [[Design Standards No. 13: Embankment Dams (Ch. 8: Seepage) | Design Standards No. 13: Embankment Dams (Ch. 8: Seepage) | {{Document Icon}} [[Design Standards No. 13: Embankment Dams (Ch. 8: Seepage) | Design Standards No. 13: Embankment Dams (Ch. 8: Seepage), USBR]] | ||
==Trainings== | ==Trainings== | ||
Latest revision as of 21:28, 28 March 2024
"Flow of water through soil can lead to movement of the soil grains. Continued movement is erosion. Many factors affect whether soil grains will move or not, including hydraulic gradient, soil plasticity, particle size, capillary tension, cementation, and others."[1]
"A review of historical dam failures indicates that nearly half of all failures of embankment dams have been a result of seepage-induced internal erosion. Additional failures due to high pore pressures or saturated slopes, both attributable to seepage water, add to the list of seepage-related historical failures. Since all soils are erodible to some extent, embankment dams are potentially susceptible to failure due to seepage. In order to evaluate new or existing dams, with respect to safety against seepage, and design defensive measures to mitigate the effects of seepage, it is important to understand the various modes of failure that can occur due to reservoir seepage acting on an embankment or its foundation."[1]
"Observations related to seepage through an earth embankment or its foundation may give an early indication of the nature, location, and severity of potential failure modes (PFMs) that may already have initiated or could initiate at higher reservoir levels. For example, vigorously flowing sand boils discharging sediment near the downstream toe of an embankment may indicate that backward erosion piping in the foundation has already initiated and that it has the potential for rapid progression. Likewise, concentrated, clear seepage at an abutment groin may be an indication of a preferential flow path through the abutment, which could provide an avenue for internal erosion at higher gradients."[2]
"Seepage collection and monitoring systems should be designed with all failure modes in mind that may reasonably be anticipated at a particular structure site, given its unique geologic characteristics and design features. Ideally, all needed seepage measurement and monitoring systems should already be in place and available to collect seepage information from the first filling on, but of course new seepage areas can emerge at any time. Once water is impounded in the reservoir, all seepage-related phenomena should be evaluated with reference to PFMs of which they could be indicators. Early identification of PFMs that may be at work can facilitate the undertaking of emergency or remedial actions that need to be performed on short notice."[2]
"Measuring seepage quantity and quality provides several important benefits:
- Comparison with Design: Measurements of actual seepage can be compared with seepage rates assumed or calculated during design to evaluate whether the dam and its various seepage control systems are functioning as intended (e.g., a foundation cutoff system or an embankment or foundation drain).
- Identifying Changes with Time: The appearance of unexpected seepage or changes in seepage quantity or quality over time can alert the dam owner to potential problems occurring within the embankment or foundation and allow for the implementation of corrective measures in a timely manner."[2]
Mitigation Measures
Examples
Best Practices Resources
Evaluation and Monitoring of Seepage and Internal Erosion (FEMA P-1032), FEMA
Design Standards No. 13: Embankment Dams (Ch. 8: Seepage), USBR
Trainings
On-Demand Webinar: Seepage Rehabilitation for Embankment Dams
On-Demand Webinar: Seepage Monitoring and Analysis of Embankment Dams
On-Demand Webinar: Relearning How to Look at Piezometric Data for Seepage Evaluation
Citations:
Revision ID: 7842
Revision Date: 03/28/2024