Ring shear tests on soil from the Vaiont landslide slip surface

The paper presents results from ring shear tests, carried out on two samples from the slip surface of the Vaiont landslide in north Italy. The tests were carried out at slow and fast rates of shearing in order to determine values of the coefficient of friction appropriate to static and dynamic aspects of the landslide. Both samples showed a significant loss of strength (negative rate effect), up to 60% below the slow residual strength, when sheared at rates of shearing greater than 100 mm/min. The observed loss of strength may explain the high acquired velocity of the landslide, or alternatively some combination of this and other mechanisms may have taken place.