A Study Of Stability And High-speed Movement Of Vajont Slide Based On Discontinuous Deformation Analysis Method

Large-scale landslides always cause catastrophic disasters for human settlements in their moving path because of the high sliding speed of an enormous volume of rocks and soils.The Vajont slide occurred in Italy is one of the most typical cases;it attracted a larger number of studies of large-scale landslides.The total duration of the landslide is merely less than one minute.The sliding mass,with the velocity of 20-30m/s,thrusted into the artificial lake,creating a tsunami about 100m high overtopped the dam and flooded five villages and small towns in the Piave River downstream,causing about 2000 casualties.At present,for the numerical simulation of Vajont landslide,there is a problem that the physical parameters of rock mass are not uniform.Furthermore,reduction of the frictional resistance of sliding band was considered to be the reason which result in rapid movement of slide mass.And previous researches mostly focus on the strength degradation of the sliding band,while the strength degradation of the sliding mass is seldom considered.In view of above problems,the Vajont slide as a case in this study,the characters of stable state and high-speed moving state are analyzed using DDA method.The influences of strength degradation of both the sliding band and the sliding mass on the landslide are also analyzed and compared in detail.The results show that:(1)A method of judging the critical state of slope failure was established.which was validated by comparing with traditional strength reduction method.In this study,initial strength of the slope was reduced a certain number of steps per time interval automatically in the process,and the critical strength is the strength value at which the displacement mutation occured.(2)The friction angle of jointed rock mass,cohesion of sliding surface and hydrostatic level have greater impacts on slope condition.The friction angle of jointed rock mass increases every five degrees,the minimum friction angle of sliding surface to maintain slope safety will reduce 0.5 degrees.Assuming that reservoir water level rises to the highest design level,safety factor of the Vajont slope reduces by about 11.9%.The safety of Vajont slope is declined to some extent due to the non-horizontal distribution of hydrostatic pressure in the joint rock mass.The effect on the stability would not be obvious unless the cohesion of the sliding surface is the same order of the normal stress.Considering that the sliding surface is in a clay interlayer and its cohesion is small,the effect of cohesion can be converted into equivalent friction angle or is not considered in the stability analysis.(3)After the Vajont landslide started along the complete length sliding surface,the strengths of the sliding surface and the sliding mass degrade considerably,and strength reduction may be the reason for the acceleration of the sliding.For the same level of strength degradation,the sliding distance is more sensitive to the strength attenuation of sliding surface than the slide mass.Under this condition,the change in the strength of the sliding mass enhances the ability of sliding mass at the sliding front to move upward at the end of the sliding slope.