Ring shear tests on soil from the Vaiont landslide slip surface

The paper presents results from ring shear tests, carried out on two sample s from the slip surface of the Vaiont landslide in north Italy The tests we re carried out at slow and fast rates of shearing in order to determine val ues of the coefficient of friction appropriate to static and dynamic aspect s of the landslide. Both samples showed a significant loss of strength (neg ative rate effect), up to 60% below the slow residual strength, when sheare d at rates of shearing greater than 100 mm/min, The observed loss of streng th may explain the high acquired velocity of the landslide, or alternativel y some combination of this and other mechanisms may have taken place.