PIPING POTENTIAL IN EARTH DAMS Investigators: Krishna Reddy

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PIPING POTENTIAL IN EARTH DAMSInvestigators
Krishna Reddy Kevin Richards, Department of
Civil and Materials Engineering Prime Grant
Support National Science Foundation
Problem Statement and Motivation

• Piping causes approximately 46 of all dam
  failures, with the backwards erosion mode of
  piping in perhaps 31 of all these piping cases
• Current methods for evaluation of backwards
  erosion piping have not been successful in
  preventing or assessing piping in unfiltered
  dams, which results in billions of dollars in
  unnecessary damages and repairs each year.
• A laboratory investigation of the constitutive
  behavior of pipe initiation is necessary to
  define key parameters that influence piping
  potential and to allow formulation of predictive
  tools and develop remediation strategies.

Key Achievements and Future Goals
Technical Approach

• Previous investigations into piping have focused
  on pipe progression. Our focus is on pipe
  initiation, which should yield a more sensitive
  tool for the prediction of the critical hydraulic
  conditions necessary to initiate piping.
• Previous investigators have found a correlation
  between confining stress conditions and critical
  piping parameters. Our work is addressing this
  phenomenon in more detail.
• Research includes conducting bench-scale
  experiments to (1) determine the critical
  hydraulic gradient and the critical discharge
  coefficient of different granular soils subjected
  to variable confining stresses in a true-triaxial
  load cell, and (2) assessing the influence
  seepage direction and the rate of change in
  hydraulic loading conditions has on the critical
  hydraulic gradient and critical discharge
  coefficient.

• Different soil types have been characterized and
  are being used in the experiments
• Preliminary results have found a relationship
  between the confining stresses and critical
  piping parameters when soils are in a non-buoyant
  condition
• The geometry of the exit also plays a large role
  in pipe initiation due to the convergence of flow
  lines at the exit point and increased gradients
  due to confinement. This explains the high
  incidence of piping failures where convergence
  effects are produced around buried structures.
• The influence of seepage direction and rate of
  change of hydraulic loading are currently being
  investigated.