Structural analysis of Turtle Mountain: origin and influence of fractures in the development of rock slope failures

Abstract

Large slope failures in fractured rocks are often controlled by the combination of pre-existing tectonic fracturing and brittle failure propagation in the intact rock mass during the pre-failure phase. This study focuses on the influence of fold-related fractures and of postfolding fractures on slope instabilities with emphasis on Turtle Mountain, located in SW Alberta (Canada). The structural features of Turtle Mountain, especially to the south of the 1903 Frank Slide, were investigated using a high-resolution digital elevation model combined with a detailed field survey. These investigations allowed the identification of six main discontinuity sets influencing the slope instability and surface morphology. According to the different deformation phases affecting the area, the potential origin of the detected fractures was assessed. Three discontinuity sets are correlated with the folding phase and the others with post-folding movements. In order to characterize the rock mass quality in the different portions of the Turtle Mountain anticline, the geological strength index (GSI) has been estimated. The GSI results show a decrease in rock mass quality approaching the fold hinge area due to higher fracture persistence and higher weathering. These observations allow us to propose a model for the potential failure mechanisms related to fold structures.

From the source area to the deposit: Collapse, fragmentation, and propagation of the Frank Slide

“…The predisposing factors and triggers were extensively discussed: from geological conditions (Allan, 1933;Cruden and Krahn, 1978;Daly et al, 1912;Humair et al, 2013;Jaboyedoff et al, 2009;McConnell and Brock, 1904;Pedrazzini et al, 2011;Terzaghi, 1950;among others), to continuing fluvial erosion (Cruden and Martin, 2007) via hydrometeorological (Cruden and Krahn, 1978) and hydrogeological conditions (Jaboyedoff et al, 2009), weathering processes (Cruden and Martin, 2007;Pedrazzini et al, 2011), seismic loading (Cruden and Krahn, 1978), and anthropic influence (Benko and Stead, 1998).…”

“…1C), which can be described as an asymmetrical thrust-fold (Humair et al, 2013) constituted by Devonian to Cretaceous carbonates and clastic rocks (Hamilton et al, 1998). The structural settings of the anticline were recently reinterpreted (Langenberg et al, 2007;Pedrazzini et al, 2011Pedrazzini et al, , 2012Humair et al, 2013), providing the characterization of the fracturing pattern of the intact rock. The rock avalanche affected four geological formations: the Palliser, Banff, Livingstone, and .…”

Three-dimensional slope stability analysis of South Peak, Crowsnest Pass, Alberta, Canada

“…In the lower section of South Peak, discontinuity set J1 has been described by several authors (e.g. Couture 1998;Pedrazzini et al 2010) as widely distributed and having a higher persistence than in the upper section. In the kinematic analysis considering the east and east-southeast faces, the presence of J1 did not influence the sliding or toppling mechanism but resulted in unstable wedges in combination with J2 and J3 (Fig.…”

“…The presence of J1 is not thought to be crucial in the development of instabilities in the upper South Peak area. The conceptual model and the displacement monitoring data for the upper area of South Peak (Froese et al 2009b;Pedrazzini et al 2008Pedrazzini et al , 2010 suggest that the "wedge zones" slide along the intersection of S0/ J3 in a northeasterly direction (plunge/trend 17°/034°), which is similar to the orientation of the measured displacement vector (Froese et al 2009b). Conversely, the presence of J1 is fundamental to explain the crack orientation and the apparent displacement vector in the lower South Peak area Froese et al 2009b).…”

“…Large open cracks and intense fracturing in the lower part of South Peak could be related to tectonic damage associated with the fold hinge and/or slope deformation associated with the instability in the upper part of South Peak ( Fig. 4a; Pedrazzini et al 2008Pedrazzini et al , 2010.…”