MECHANISMS AND KINEMATICS OF RIVER VALLEY LANDSLIDES IN EDMONTON

A study of three translational landslides along the North Saskatchewan River Valley in Edmonton is presented in this paper. The major focus is on kinematics and mechanisms of deep seated landslides in bedrock of the Upper Cretaceous Horseshoe Canyon Formation. The study found that the river valley landslides are caused by a combination of several factors, including toe erosion by the river, the effects of residential development behind the slope crests including the rise of groundwater levels, and softening of the bedrock materials at the valley wall. The landslides developed in stages starting as a minor toe failure and gradually retrogressing upslope. Development of landslide stages observed in the North Saskatchewan River Valley can be described as follows; • Pre-failure slope movement can be characterized by minor failures at the toe and the mid-slope area. • Major slope failure can range from several days to several years. The rate of movements depends on type and thickness of the overburden materials and the bedrock above the surface of rupture. • During the major slope failure, the main body translates along the surface of rupture and a distinct graben feature appears at the head of the displaced material due to subsidence. • After a major failure, displaced material rests on the rupture surface and the factor of safety improve with the new slope configuration. During this period, some changes in the external condition such as increase in groundwater level, changes in slope configuration and loading at the slope crest can reduce the factor of safety to below unity.