Retrofitting graded chimney drain using bio-polymer slurry at Hays Creek Dam, New Zealand

Raj Jairaj

Safety review studies showed that the Hays Creek Dam was prone to an uncontrolled piping failure during or after an earthquake due to filter incompatibility between the clay core and shell material. The discussion is in regard to the geotechnical aspects that were dealt with the upgrading design and construction of this dam in 1993 /1994.

Options considered for upgrading varied from providing an upstream impermeable membrane, introduction of a plastic concrete core, or to demolish and rebuild the dam. However the introduction of sand chimney drain using a bio polymer proved to be the most attractive option to be followed. Although this technology has been used in the last decade in the construction of deep drainage trenches in other parts of the world this is the first time it has been successfully adopted for an operating dam. The extracts of the discussion provides an insight into some of the construction ‘surprises’ that were encountered in adopting this technology on this location and how they were successfully overcome. The dam has now been brought back into operation and the initial monitoring data show little surprise.

Speaker biography

Raj is a Geotechnical Engineer with over 40 years experience in the Investigation, Design and Upgrade works for major dam. He has worked in Sri Lanka, Singapore, Malaysia, New Zealand and Australia in a variety of projects.
Throughout his career, his focus has been on design of new dams and upgrade works on existing dams and large irrigation levy system. Landslides related to dams and road embankments are another area of interest to Raj.

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