More than ten years of surface subsidence observation on Tersanne and Etrez storage cavity fields in France, is subject to numerical analysis, using a mixed boundary and finite element approach. The consideration of large domains to discretize and non linear behaviours to take into account is simplified as the bedded rock mass is modelled in two horizontal strata : an elastic clay cover and a viscous salt bed, the first one discretized in boundary elements and the second in finite elements. Although the problem is typically three-dimensional, an axisymmetric model for a single cavity is used throughout the numerical analysis, and a superposition method, previously validated, is applied to a 14-cavity field. There is a reasonable agreement between in situ data and numerical results.