Internal Erosion – Applying Erosion Mechanics From ICOLD Bulletin 164 In Internal Erosion Failure Mode Analyses

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Internal erosion causes about half of all failures of water-retaining earth embankment dams. Similar statistics apply to levees. Internal erosion occurs when the hydraulic loads imposed by water seeping through the pores or flowing through cracks and openings in the soils in embankments and their foundations generate erosive forces sufficient to overcome the resistance to erosion of those soils. The knowledge of internal erosion processes has advanced significantly over the past two decades. The two volumes of ICOLD Bulletin 164 (ICOLD 2017, ICOLD, 2016) reflects the results of a group of international experts to collect information from experience, case histories and research to provide guidance on internal erosion for engineers in dams and levees. The accumulation of knowledge led to the definition and understanding of the mechanics of the four modes of internal erosion. This understanding of internal erosion mechanics makes it possible for engineers to estimate the hydraulic load that will likely cause internal erosion to failure. The mechanics of the modes of internal erosion (mechanisms) can be combined with the internal erosion pathways through embankments and their foundations to developed detailed descriptions of potential failure modes (PFMs). If desired these detailed PFM descriptions can be used in quantitative risk analyses. This webinar will include discussion of all of the concepts described above, with reference to how the Bulletin provides a reference to the application of these concepts in dam safety evaluations and risk analyses.

Five Learning Objectives of This Course:

Exposure to the international knowledge concerning internal erosion reflected in ICOLD Bulletin 164
Understanding of the four mechanisms of internal erosion (IE)
Understanding of how IE mechanisms combine with pathways to create potential failure modes
Improved ability to estimate IE erosion risks, both quantitatively and qualitatively
Improved ability to identify vulnerabilities to internal erosion for existing dams and levees

Rodney Bridle

Principal, Dam Safety Ltd.

Rodney Bridle is the UK Member of the ICOLD Technical Committee on Embankment Dams. He is the editor and part-author of the two volumes of ICOLD Bulletin 164 on Internal Erosion in Existing Dams, Dikes and Levees, which deal primarily with the mechanics of internal erosion. To spread this important new knowledge he has written papers, participated in workshops and made many presentations around the world. Rod is a widely experienced consulting civil engineer specializing in the performance and safety of embankment dams. His particular present interest is in applying new and old knowledge to understand the behavior of the now large numbers of existing embankment dams and levees to make them safe and economically effective. He has completed many quantitative risk assessments using UK guidance; some were presented at ASCE Geo-risk in Denver in 2017 and at ICOLD in Vienna in 2018. He has supervised substantial and minor safety works at dams vulnerable to internal erosion. He is a member of BC Hydro’s Expert Engineering Panel with Emeritus Professor Robin Fell (University of New South Wales, Australia) and Dr Kaare Hoeg (Norwegian Geotechnical Institute) reviewing the seepage control functions of existing high dams in Canada. He was a Partner and Director of Watson Hawksley and Montgomery Watson (later MWH, now Stantec) and is a former Chair of the British Dam Society and a life member of USSD.

John W. France, P.E., D.GE, D.WRE

President, JWF Consulting, LLC

JWF Consulting, LLC.

Mr. France has more than 45 years of consulting engineering experience. Most of his technical work for the past 37 years has focused on dams and water retention structures. He has been responsible for the analysis, design, and construction of embankment and roller compacted concrete dams and their appurtenant structures. He has served on numerous senior technical review boards and panels for dam safety projects for the U.S. Department of the Interior, Bureau of Reclamation, U.S. Army Corps of Engineers, BC Hydro, and Brookfield Renewable Energy. Mr. France was the team leader for the Independent Forensic Teams tasked with investigating the 2017 Oroville Dam, CA spillway incident and the 2020 failures of Edenville and Sanford Dams, MI.

INTERNAL EROSION AS SEEN BY ICOLD BULLETIN 164
- Introduction to ICOLD
- Need for guidance – failures, fatalities, speed of failure
- Bulletin responds to needs – new knowledge
- Mechanics of internal erosion – failures when water level high during floods
- Four internal erosion failure modes, estimating water levels causing internal erosion failure, case histories
- Contact erosion
- Concentrated leak erosion
  - Crack locations
  - Filter erosion boundaries approach to filtering capacity of dam fill
  - Vulnerability at spillways and culverts
- Suffusion
- Backward erosion (and piping)
- Summary of four modes of erosion mechanics
- Addressing internal erosion potential in dams – before critical flood occurs
INTERNAL EROSION FAILURE MODE ANALYSES & RISK ASSESSMENT
- Examples of potential failure routes
- Events where subjective assessments necessary
- How using ICOLD Bulletin 164 will improve PFMA
- Probability estimation for risk analysis
- Probability estimated from critical flood level from ICOLD 164 internal erosion analyses
- Some examples of internal erosion risk assessment
SUMMARY & RECOMMENDATIONS