ABSTRACT
Sinkholes can develop above deep-lying brine-filled caverns in salt. The basic mechanism is sliding of large columns of rock along overburden joints under the influence of joint fluid pressure. Loss of salt back integrity, i.e. hydraulic connection of the cavern-filling brine to the overburden joints with pressure-driven percolation is the starting point which may lead to sinkhole formation. The sliding of rock columns is linked to the small-scale tectonic fragmentation of the rock mass in the overburden. We present some examples, conceptual and analytical estimates, and results of numerical studies which illustrate the mechanism in single-cavern situations and interacting caverns in cavern fields. In contrast to most situations that are well-described by a continuum simulation approach, sinkhole formation and block sliding instabilities in the overburden are fundamentally discontinuous processes. The overburden is often brittle, so that the shear resistance of joints and fractures is characterised by an adhesive peak strength and subsequent softening. In such cases, hydromechanical coupling is crucial for a stability analysis. Therefore, appropriate constitutive models for rocks and joints and a consistent discontinuous modeling approach are required.
