Considerations for Embankment Dam Toe Drain Design: An Inspection and Maintenance Perspective

One of the key components in modern embankment dam design is the toe drain system, which reduces pore pressures in the downstream face and toe of the embankment and conveys seepage away from the dam. While toe drain design is not new to the dam building industry, challenges associated with the long-term requirements for modern inspection and maintenance techniques have not been well documented. Inspection and maintenance of toe drain systems is an important component of embankment dam safety, since the potential for internal erosion may exist within an inadequate system. It is important for design engineers to familiarize themselves with inspection and maintenace issues commonly encountered in the field, and to account for them in the design. The purpose of this study is to "close-the-loop" of knowledge regarding challenges observed in the field and how they relate to what is designed in the office. This paper will highlight issues found in toe drain systems related to environmental factors and common obstructions; pipe material, size, slope, bends, and depoth; filtering and perforations; inspection wells, seepage monitoring instrumentation, and terminations; vehicular access; security and protection; and construction considerations. Work published on the topic will eb incorporated and synthesized with case studies from high-hazard dams in the Bureau of Reclamation's dam inventory to highlight specific problems associated with various types of toe drain designes. Based on these findings, a summary of considerations will be given for embankment toe drain design.