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 post-folding 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.