Monitoring based time-prediction of rock falls: Three case-histories

Three case-histories are aimed to show possibilities how to use results of dilatometric measurements of relative displacements on rock cracks to asses s actual rock slope instability and to make time-predictions of a rock fall . The prediction of a collapse of a sandstone rock wall above an internatio nal road in the Northern Bohemia was made 2 months beforehand, and the crit ical 7-days time-window was met with 1-day precision. For an unstable sands tone cliff in the same geographic area, the beginning for the the final pha se of a rock fall preparation was foreseen 1 year before. The prognosis of the month entailing immediate rock fall danger was made 5 months beforehand , and then proved using a monitoring method. The time series of a 2 years l asting monitoring enabled the long-time prognosis of rock falling activity from a limestone cliff in Austrian Alps, in 1990. At present time, the prog nosis seems to become fulfilled in the next 2 years. These years are making the upper limit of its most probable time window. The needs to improve met hods of the medium- and the longtime ranging prognostication to meet the ma jority of practical demands are briefly discussed. (C) 2000 Elsevier Scienc e Ltd. All rights reserved.