Modélisation de la propagation, en mode lent et en mode dynamique, d'un fontis à l'aide du code de calcul UDEC

International audienceThe propagation of sinkhole phenomena towards the surface is a fairly complex phenomenon, with the potential to cause damage to surface structures within the affected area. Using numerical modelling a methodology has been developed which makes it possible more closely to specify the conditions in which sinkhole forms and to propose a prediction model. The UDEC code is used. An actual case of sinkhole in the Paris region (Vachat, 1982) has been used as a basis for the study. We simulated the predicted collapse mechanism and the profile of the sinkhole itself. The influence of a surface structure was also examined. The modelling process in static and dynamic modes was developed in order to simulate the ways in which sinkhole forms. As regards dynamic modelling, we determine the relevant parameters: critical damping and fundamental frequency. The dominant point in this method is that induced fractures in the roof strata overlying underground excavations - the root cause of sinkhole - are created by hand. The fractures were induced using the criterion whereby a zone is formed in which the failure criterion is exceeded. The comparison between observation and the modelling results is very satisfactory. It may be noted that the numerical modelling and the methodology used enabled us to determine the shape and parameters of the roof "bell" and of the zone of sinkhole. We were also able to confirm the influence of external loads that might facilitate development of the sinkhole. A feature of dynamic (rapid) appearance of sinkhole is apparently that it takes place on a bigger scale. Incidentally such an approach could be used to examine the consequences for structures