Geotechnical Characterization of Clearwater Shales for Design

M. Pinheiro

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

Session: SOIL AND TERRAIN CHARACTERIZATION - IV In-Situ Geotechnical Testing

ABSTRACT: Clearwater Formation shales are heavily overconsolidated clay- and silt-shales encountered within the footprint of several oil sands mines located in northeastern Alberta, Canada. Their micro- and macro-structures are often associated with very low shear strengths as demonstrated in this paper by the results of several direct shear tests carried out on Clearwater shale samples from the Joslyn North lease, located north of Fort McMurray, Alberta. An important structural feature of these weak rocks is the occurrence of slickensides, i.e. smoothly polished surfaces caused by the frictional movement along the sides of a fault plane and usually linked with low shear resistance. Identifying these structural discontinuities in the field is critical for the design of earthen structures founded on these weak materials. At the Joslyn North lease, slickenside occurrences were identified sparsely throughout the site; however, nearly 98% of the occurrences were observed in augered test holes. A geotechnical test pit program was implemented in the winter of 2014 to characterize more accurately the nature of these defects. No evidence of distinct shear zones or slickensides was found, despite their description in adjacent boreholes, confirming that the slickensides previously described in augered test holes were in fact drill-induced.

RÉSUMÉ: --strucpar les résultats de nombreux essais de cisaillement effectués sur des échantillons de shale du Clearwater provenant de la concession pétrolière de Joslyn North, située au nord de Fort McMurray en Alberta. Un aspect important de ces roches normalement associées à une faibterrain est cruciale dans la conception de structures en terre fondées sur ces matériaux de faible résistance. Sur la concession de Joslyn North, quelques surfaces pure de ces défauts. Aucune évidence de zones de cisaillement nt que ces surfaces polies étaient en fait induites par le forage.

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