2013 – Seismic evaluation of embankments for the Tekapo Canal remediation project

Lelio Mejia and Ethan Dawson

The 26 km long Tekapo Canal is a major component of the Upper Waitaki Power Scheme in the Mackenzie Basin in New Zealand’s South Island. The canal, commissioned in 1977, conveys water from a power plant at Lake Tekapo to a power plant at Lake Pukaki. To support a re-lining and repair works project along sections of the canal, seismic deformation analyses were performed. Earthquake-induced settlements and deformations for three critical embankment sections were estimated. Two dimensional, nonlinear, dynamic numerical analyses were performed with the computer code FLAC. Analyses were performed for the Maximum Design Earthquake (MDE), the Serviceability Level Earthquake (SLE) and for aftershocks of various magnitudes. A critical feature in the repairs and upgrades was a geosynthetic liner to be placed along portions of the canal. Seismic performance of this liner would be affected by cracking in the underlying embankment. Crack size estimates (width and depth) were developed based on evaluation of the computed deformations and the empirical correlations of Fong and Bennett (1995) and Pells and Fell (2002). Calculated deformations were generally small, and indicative of adequate seismic stability. Recommended design crack widths for the MDE ranged from 20 to 50 mm, while recommended design crack depths for the MDE ranged from 1.0 to 2.5 m.