Problem Statement and Motivation

1. 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.