In-situ large monitoring and numerical modeling of the loss of stability of salt cavity

Abstract : During several years, a fulfilled brine salt cavity was monitored in The North-East of France (Lorraine) in order to analyze times evolutions of several variables (microseismicity, subsidence) using geophysical and geomechanical monitoring. In addition, continuous and mixed (discontinuous-continuous) non-linear numerical computations were performed in order to predict the mechanical collapse conditions of the cavity. At given cavity sizes, the collapse appeared mainly controlled by the value of the brine pressure in the cavity and by the strength of a stiff dolomite rock layer located at the top of the cavern. The control of the collapse was performed by decreasing smoothly the brine pressure up to the failure (collapse of the cavern and of the overburden rock layers). Comparison between experimental data and numerical computations allows describing quite accurately the time evolution of failure. The mechanisms of failure are analyzed and some physical interpretation are given concerning this collapse.