Garrett Jackson and Dennis Miller of the Colorado Division of Water Resources summarise the lessons learned at an advanced technical seminar on seepage for earth dams
THE ‘Seepage for Earth Dams’ seminar, a component of the Association of State Dam Safety Officials (ASDSO) advanced technical programme of study, was held from 28-30 October 2003, on the campus of the University of Colorado in Boulder, US. Instructors included Keith Ferguson , Steve Poulos, and Jim Talbot from GEI Consultants and Alfredo Urzua of Boston College and Prototype Engineering, who presented a concise, thought-provoking programme throughout the three-day course. The 67 attendees represented a broad range of perspectives and included representatives from state regulatory agencies, the federal government, private consultants and dam owners. Not surprisingly, most attendees were from Colorado and nearby western states, but the seminar also drew participants from as far away as Florida, Georgia, Maryland and Mississippi, as well as a group of three from Puerto Rico.
The seminar topics included general and technical discussions of the principles of seepage through porous media (specifically earth dams and their earth and rock foundations), field and laboratory investigations of permeability, seepage analyses using both flow nets and numerical models, the fundamentals of seepage control using natural and synthetic materials, design criteria for filters and drains in dams and foundations, and quality control in the construction of seepage control systems. Case histories of both successful and unsuccessful seepage control designs were reviewed to illustrate the points of the discussions. The case histories covered a wide range of relevant topics including:
• Discussions of drain capacity vs. filter criteria in design and construction of a seepage control system.
• Development and effects of piping.
• Karst and solution-prone materials.
• Dewatering for stability and control of seepage.
• Effects of seepage on dispersive soils.
• Seepage control and seismic concerns.
• Effects of dam penetrations, such as outlet conduits, on seepage development.
• Concrete facing as a seepage barrier.
• Instrumentation systems for existing dams.
The instructors demonstrated their considerable experience in
and knowledge of the field of seepage and its effect on earth dams. The attendees were able to discuss many of their specific questions with the presenters and other attendees in an open exchange of ideas and experience.
A comprehensive and detailed bound set of course notes covering all of the discussion topics and case histories presented, including photos, graphs, charts and illustrations, was provided to all attendees, and should prove a valuable addition to the professional libraries of all who attended. Going far beyond the mere listing of significant technical references typically provided at technical seminars, the instructors assembled and provided to the attendees, in a separate volume, a complete and readily-usable set of some of the more significant technical references in the field of earth dam seepage, ranging from an excerpt of Henri Darcy’s classic 1856 book describing his derivation of his now-famous law defining seepage flow through porous media, to Arthur Casagrande’s classic 1930s vintage papers and Harvard class notes on embankment dam seepage, to mid-1990s reference describing the current state of practice for filter design.
Overall, the course appeared to be well-received by the attendees, with the general consensus that the information and knowledge passed along by the instructors would prove useful in the evaluation of embankment dam safety.
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