Geomechanics of a Snowmelt-Induced Slope Failure in Glacial Till

An integrated approach involving field, laboratory and numerical investigations was undertaken to study the progressive deformation mechanism of a slope in glacial till above the Town of Alta, Utah that experienced catastrophic failure due to rapid snowmelt in June 2010. Detailed geometry of the slope surface and of the exposed sliding surface obtained from global positioning system surveying together with strength and stress–strain parameters derived from laboratory triaxial tests on undisturbed samples of glacial till collected from the landslide site were employed with finite-element modeling to examine the effects of an increase in snowmelt-induced perched water table on the yielding behavior of the slope prior to catastrophic failure. The numerical results indicate gradual development of a plastic yield zone along the sliding surface with progressive rise in the perched water table above the toe of the slide mass, which was spreading out throughout the slide mass at the stage corresponding to the onset of catastrophic slope failure. The evolution of the slope safety factor obtained from limit-equilibrium stability analyses in relation to the development of the finite-element computed yield zone along the sliding surface is also discussed.