Experimental and numerical evaluation of stress redistribution in thick-walled rocksalt cylinders

Abstract Whenever an opening is excavated in soft rocks showing elastic–visco-plastic behaviour, like rocksalt and potash, the stress state prevailing soon after the excavation will not remain constant in time but will eventually evolve from the initial state, σ o , generally considered to be elastic, to a state of stress that can be considered to be stationary for all practical purposes, σ ss . The knowledge of the stress state prevailing around the excavation some time after its completion is essential for many short-term applications such as the interpretation of in situ tests based on the cavity expansion principle and of stress measurements based on overcoring techniques. Since no analytical solutions are available for the evaluation of this stress redistribution process, numerical analyses are often used to study this problem. The results obtained from such analyses depend on many factors but mainly, the kind of creep law formulation and related parameters. This paper presents an experimental methodology to quantify the amount of stress redistribution occurring in a thick-walled cylinder under a given set of conditions. This experimental methodology does not require any assumption regarding the creep behaviour of the material. As a consequence, it allows the validation of numerical analyses by comparing the amount of stress redistribution obtained experimentally and that obtained from these numerical analyses.