ABSTRACT: Electrical resistivity imaging for investigating slope stability, Fort St. John, British Columbia.

CGRG Bibliography of Canadian Geomorphology
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Abstract

The Peace River District of northeastern British Columbia is characterized by steep river valleys that have been incised up to 300 m deep in poorly consolidated Cretaceous and Quaternary sediments. Since the area is a major producer of oil and gas, numerous pipelines and roads transect these valleys. Slope stability has been a major problem at several locations and will continue to pose a problem for future development in the area. Understanding the mechanisms of slope stability will allow better assessment of the risks to infrastructure. The Geological Survey of Canada is conducting studies to determine the role that groundwater infiltration and flow have in controlling slope movements. Near-surface geophysical surveys provide a quick non-invasive method of investigating ground conditions. Since moisture content of the underlying strata plays an important role in slope stability, electrical methods are particularly suitable. For this study, two-dimensional electrical resistivity imaging was conducted along three pipeline route slopes in the Fort St. John area during July 2002. An automated electrical resistivity imaging system was used to acquire continuous Wenner array images up to 1300 m in length. The system used 48 electrodes spaced 5 m apart, to obtain a high-resolution image of the sub-surface with an exploration depth of approximately 40 m. Two-dimensional inversion software was used to obtain topography-corrected electrical resistivity models for each slope. Borehole information was incorporated in the interpretation of the results. Electrical resistivity imaging proved to be a fast and effective method for investigating the extremely steep slopes encountered in the Fort St. John area. The results indicate that the method is very useful in identifying seepage zones and extending hydrostratigraphy from borehole observations. These studies will assist modeling of groundwater flow by confirming areas of predicted groundwater discharge and by delineating areas where moisture content changes are taking place.

Bibliography of Canadian Geomorphology