Embankment Failures – Local Experiences

There have been six embankment dam failures, 40 notices issued for non-compliance with the Building Act (2004), and five abatement notices issued under the Resource Management Act (1991) in respect to small irrigation dams in Otago since 2011. Investigations into three failures in Otago, and one access embankment on the West Coast, are used to illustrate common mechanisms of failure and how these could have been mitigated by good engineering practice. Each case study is summarised, a probable failure mechanism postulated, and remedial measures to avoid recurrence identified. These case studies present common examples from the spectrum of failures associated with these structures, including: foundation/fill contact piping, spillway failure, piping of the conduit, and overtopping. Common design elements to prevent, minimise the likelihood of, or safeguard against failure are introduced, and the challenges of implementing these post-failure emphasized. Because failures tend to develop very rapidly, the importance of getting the right level of design input and QA with any potentially hazardous water retaining structure, irrespective of the size of the structure, is emphasized.