Long term monitoring and numerical modelling of self-potential for seepage surveillance at the Mactaquac dam, New Brunswick, Canada

A. Ringeri

In the proceedings of: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: SOIL AND TERRAIN CHARACTERIZATION - IX Geophysical Methods

ABSTRACT: The self-potential (SP) method is a geophysical technique that is capable of measuring streaming potential generated by seepage flow. Continuous monitoring of 62 non-polarizing electrodes has been underway near the interface of an embankment dam and concrete diversion sluiceway at the Mactaquac Generating Station since April of 2013. The electrode array consists of 30 embankment electrodes covering a 20 × 54 m area on the downstream slope and 32 borehole electrodes distributed along a 50 m long subvertical borehole within the diversion sluiceway structure. The observed electric potentials are attributed to a combination of geomagnetically induced telluric currents, and SP fields associated with hydrological, seepage, and other unknown mechanisms. Numerical modelling of streaming potential were carried out using Finite Element Analysis (FEA) of a 2D dam model. The numerical simulations agreed within one order of magnitude of SP observed between September to November and demonstrate that the general shape and magnitude of the observed profile is likely the result of seepage. However, the simulations failed to replicate an anomaly of unknown origin found near the embankment toe. The stability and repeatability of SP data acquired over 3 years suggests that surface SP monitoring can be a viable technique for the long term surveillance of foundation conditions.

RÉSUMÉ: La méthode de polarisation spontanée (PS) est une technique géophysique pour mesurer les potentiels électriques des infiltrations. Depuis avril 2013 la surveillance en continu de 62 électrodes non Centrale de Mactaquac. Le réseau se compose de 30 électrodes de remblai couvrant une surface de 20 m sur 54 m dans en béton. Les potentiels électriques observés sont attribués à une combinaison de courants telluriques par analyse aux observée pendant la période de septembre à novembre, mais échouent à reproduire une anomalie constatée près du pied du remblai. La stabilité et la reproductibilité des données de PS collectées en trois ans suggèrent que la surveillance de

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