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~G4 ._ M. L. JEREMIC SU6SIDENCE FROM SOLUTION MINING OF SALT 2O5 Subsidence of the surface often occurs in two dis- tinct stages, beginning with gradual settling but acceler- ating to a rapid collapse as the active zones of failure progress from the underground excavation to the surface. MECHANISM OF SUDSIDENCE The mechanism of subsidence may be explained by the The development of subsidence in the city of Tuzla, Yugoslavia, over a salt horizon which had been extracted by solution mining for centuries is described. Surface profiles and the deformations of buildings show the dif- ferent zones of movement. lowering and breaking of the strata overlying the cavities caused by solution mining aspects of deformation There are two inter-related The first is manifested in the ' bedrock below the surface, termed subsurface subsidence. • The second one is manifested on the ground surface and the process is termed surface subsidence. Subsurface subsidence caused by solution mining has no satisfactory mathematical or empirical theories to ex- plain its mechanism due to the fact that it can not be observed. The quantity and geometry of the rock salt remnants left by solution mining are unknown. It is al- most impossible to relate the configuration of one or more cavities in underlying salt beds to the collapse of the rock salt and overlying strata. The general hypothetical model of subsurface subsidence is based on the assumption that profiles of the cavities in most rock salt deposits exhibit a form similar to a loaded thick beam with clamped edges. The events of deformations might~be in the following order: 1. The postulated thick beam comprised of the roofing strata is subjected to gravitational body Forces, whose magnitude depends on the strata thickness (Fig. la).